Notes

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cal
Displays a calendar
Syntax
cal [−smjy13] [[[day] month] year]
Description
View calendar of specific month or year
Options
−1 Display single month output. (This is the default.)
−3 Display prev/current/next month output.
−s Display Sunday as the first day of the week.
−m Display Monday as the first day of the week.
−j Display Julian dates (days one-based, numbered from January 1).
−y Display a calendar for the current year.
−V Display version information and exit.
Example 1
cal prints an ASCII calendar of the current month
[eleiss@eleiss ~]$ cal
August 2011
Su Mo Tu We Th Fr Sa
1 2 3 4 5 6
7 8 9 10 11 12 13
14 15 16 17 18 19 20
21 22 23 24 25 26 27
28 29 30 31
cal, when used without an argument, prints calendar of current month
Example 2
To view the calendar of a specific year, provide the year as an argument
[eleiss@eleiss ~]$ cal 2000
2000
January February March
Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa Su Mo Tu We Th Fr Sa
1 1 2 3 4 5 1 2 3 4
2 3 4 5 6 7 8 6 7 8 9 10 11 12 5 6 7 8 9 10 11

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9 10 11 12 13 14 15 13 14 15 16 17 18 19 12 13 14 15 16 17 18
16 17 18 19 20 21 22 20 21 22 23 24 25 26 19 20 21 22 23 24 25
23 24 25 26 27 28 29 27 28 29 26 27 28 29 30 31
30 31
April May June
1 1 2 3 4 5 6 1 2 3
2 3 4 5 6 7 8 7 8 9 10 11 12 13 4 5 6 7 8 9 10
9 10 11 12 13 14 15 14 15 16 17 18 19 20 11 12 13 14 15 16 17
16 17 18 19 20 21 22 21 22 23 24 25 26 27 18 19 20 21 22 23 24
23 24 25 26 27 28 29 28 29 30 31 25 26 27 28 29 30
30
July August September
1 1 2 3 4 5 1 2
2 3 4 5 6 7 8 6 7 8 9 10 11 12 3 4 5 6 7 8 9
9 10 11 12 13 14 15 13 14 15 16 17 18 19 10 11 12 13 14 15 16
16 17 18 19 20 21 22 20 21 22 23 24 25 26 17 18 19 20 21 22 23
23 24 25 26 27 28 29 27 28 29 30 31 24 25 26 27 28 29 30
30 31
October November December
1 2 3 4 5 6 7 1 2 3 4 1 2
8 9 10 11 12 13 14 5 6 7 8 9 10 11 3 4 5 6 7 8 9
15 16 17 18 19 20 21 12 13 14 15 16 17 18 10 11 12 13 14 15 16
22 23 24 25 26 27 28 19 20 21 22 23 24 25 17 18 19 20 21 22 23
29 30 31 26 27 28 29 30 24 25 26 27 28 29 30
31
The above command displays the calendar of year 2000
Example 3
To view the calendar of a specific month, provide the month and the year as arguments
[eleiss@eleiss ~]$ cal 1 1990
January 1990
Su Mo Tu We Th Fr Sa
1 2 3 4 5 6
7 8 9 10 11 12 13
14 15 16 17 18 19 20
21 22 23 24 25 26 27
28 29 30 31
The above command displays the calendar for January 1990
Example 4
The option -3 displays the calendar of the specified month along with its previous and next month
[eleiss@eleiss ~]$ cal -3 8 1947
July 1947 August 1947 September 1947
1 2 3 4 5 1 2 1 2 3 4 5 6
6 7 8 9 10 11 12 3 4 5 6 7 8 9 7 8 9 10 11 12 13
13 14 15 16 17 18 19 10 11 12 13 14 15 16 14 15 16 17 18 19 20
20 21 22 23 24 25 26 17 18 19 20 21 22 23 21 22 23 24 25 26 27

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27 28 29 30 31 24 25 26 27 28 29 30 28 29 30
31
The above command displays the calendar for July, August and September 1947
date
print or set the system date and time
Syntax
date [OPTION]... [+FORMAT]
date [-u|--utc|--universal] [MMDDhhmm[[CC]YY][.ss]]
Description
Display the current time in the given FORMAT, or set the system date.
Options
-d, --date=STRING
display time described by STRING, not `now'
-f, --file=DATEFILE
like --date once for each line of DATEFILE
-r, --reference=FILE
display the last modification time of FILE
-R, --rfc-2822
output date and time in RFC 2822 format. Example: Mon, 07 Aug 2006 12:34:56 -0600
--rfc-3339=TIMESPEC
output date and time in RFC 3339 format. TIMESPEC=`date', `seconds', or `ns' for date and time to
the indicated precision. Date and time components are separated by a single space: 2006-08-07
12:34:56-06:00
-s, --set=STRING
set time described by STRING
-u, --utc, --universal
print or set Coordinated Universal Time
Formats
%d day of month (e.g, 01)
%m month (01..12)
%Y year
%F full date; same as %Y-%m-%d
%H hour (00..23)

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%k hour (0..23)
%M minute (00..59)
%S second (00..60)
%T time; same as %H:%M:%S
Invoking date with no FORMAT argument is equivalent to invoking it with a default format that depends
on the LC_TIME locale category. In the default C locale, this format is '+%a %b %e %H:%M:%S %Z %Y',
so the output looks like Thu Mar 3 13:47:51 PST 2005.
Example 1
Show current date and time.
[eleiss@eleiss ~]$ date
Tue Aug 16 18:37:07 IST 2011
[eleiss@eleiss ~]$
date command shows current date and time when run without arguments.
Example 2
Show time in hh:mm:ss format
[eleiss@eleiss ~]$ date +"%H:%M:%S"
18:41:20
[eleiss@eleiss ~]$
If given an argument that starts with a `+', `date' prints the current date and time in the format defined by
that argument.
Example 3
Display time described by STRING.
[eleiss@eleiss ~]$ date +"%d-%m-%Y" -d "1 January"
01-01-2011
[eleiss@eleiss ~]$
prints the date and time specified by -d in format defined by the argument.
bc
An arbitrary precision calculator language
Syntax
bc [ -hlwsqv ] [long-options] [ file ... ]

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Description
bc is a language that supports arbitrary precision numbers with interactive execution of statements. There
are some similarities in the syntax to the C programming language. A standard math library is available by
command line option. If requested, the math library is defined before processing any files. bc starts by
processing code from all the files listed on the command line in the order listed. After all files have been
processed, bc reads from the standard input. All code is executed as it is read.
Options
-l, --mathlib
Define the standard math library.
-w, --warn
Give warnings for extensions to POSIX bc.
-s, --standard
Process exactly the POSIX bc language.
-q, --quiet
Do not print the normal GNU bc welcome.
Numbers
The most basic element in bc is the number. There are two attributes of numbers, the length and the
scale. The length is the total number of significant decimal digits in a number and the scale is the total
number of decimal digits after the decimal point.
For example:
.000001 has a length of 6 and scale of 6.
1935.000 has a length of 7 and a scale of 3.
Variables
There are four special variables, scale, ibase, obase, and last.
scale defines how some operations use digits after the decimal point. The default value of scale is 0.
ibase and obase define the conversion base for input and output numbers. The default for both input and
output is base 10.
last (an extension) is a variable that has the value of the last printed number.
Expessions
- expr The result is the negation of the expression.
++ var The variable is incremented by one and the new value is the result of the expression.
-- var The variable is decremented by one and the new value is the result of the expression.
var ++
The result of the expression is the value of the variable and then the variable is incremented by one.
var --

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The result of the expression is the value of the variable and then the variable is decremented by one.
expr + expr
The result of the expression is the sum of the two expressions.
expr - expr
The result of the expression is the difference of the two expressions.
expr * expr
The result of the expression is the product of the two expressions.
expr / expr
The result of the expression is the quotient of the two expressions.
expr % expr
The result of the expression is the "remainder".
expr ^ expr
The result of the expression is the value of the first raised to the second.
( expr )
This alters the standard precedence to force the evaluation of the expression.
var = expr
The variable is assigned the value of the expression.
var = expr
This is equivalent to "var = var expr" with the exception that the "var" part is evaluated only once.
expr1 < expr2
The result is 1 if expr1 is strictly less than expr2.
expr1 <= expr2
The result is 1 if expr1 is less than or equal to expr2.
expr1 > expr2
The result is 1 if expr1 is strictly greater than expr2.
expr1 >= expr2
The result is 1 if expr1 is greater than or equal to expr2.
expr1 == expr2
The result is 1 if expr1 is equal to expr2.
expr1 != expr2
The result is 1 if expr1 is not equal to expr2.
!expr The result is 1 if expr is 0.
expr && expr
The result is 1 if both expressions are non-zero.
expr || expr
The result is 1 if either expression is non-zero.
Math Library

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If bc is invoked with the -l option, a math library is preloaded and the default scale is set to 20. The math
library defines the following functions:
s (x) The sine of x, x is in radians.
c (x) The cosine of x, x is in radians.
a (x) The arctangent of x, arctangent returns radians.
l (x) The natural logarithm of x.
e (x) The exponential function of raising e to the value x.
Example 1
Demonstrate bc command.
[eleiss@eleiss ~]$ bc
bc 1.06.95
Copyright 1991-1994, 1997, 1998, 2000, 2004, 2006 Free Software Foundation,
Inc.
This is free software with ABSOLUTELY NO WARRANTY.
For details type `warranty'.
4+8
12
4*5
20
5-3
2
6/3
2
6%3
0
2^10
1024
10*5+4
54
10*(5+4)
90
Unlike other commands, when you run bc command dollar prompt ($) is not displayed on the screen. This
indicates that bc is ready to take input from you.
Example 2
Demonstrate expressions in bc command.
[eleiss@eleiss ~]$ bc -q
var=100
var
100
20 < 10
0
20 > 10
1

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20 > 10 && 30 > 20
1
20 > 10 || 30 < 20
1
20 > 10 && 30 < 20
0
When expression is true, it returns 1 and 0 for false.
Example 3
Arithmetic library in bc.
[eleiss@eleiss ~]$ bc -l
bc 1.06.95
Copyright 1991-1994, 1997, 1998, 2000, 2004, 2006 Free Software Foundation,
Inc.
This is free software with ABSOLUTELY NO WARRANTY.
For details type `warranty'.
s(1)
.84147098480789650665
c(1)
.54030230586813971740
l(1000)
6.90775527898213705205
If bc is invoked with the -l option, a math library is preloaded and the default scale is set to 20.
This example calculates sine, cosine and logarithm.
echo
Display a line of text.
Syntax
echo [SHORT-OPTION]... [STRING]...
echo LONG-OPTION
Description
Echo the STRING(s) to standard output.
Options
-n do not output the trailing newline
-e enable interpretation of backslash escapes
-E disable interpretation of backslash escapes (default)
Escape Sequence

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If -e is in effect, the following sequences are recognized:
backslash
a alert (BEL)
b backspace
c produce no further output
e escape
f form feed
n new line
r carriage return
t horizontal tab
v vertical tab
0NNN byte with octal value NNN (1 to 3 digits)
xHH byte with hexadecimal value HH (1 to 2 digits)
Fonts Properties
echo command can change font style, background color of fonts and font colors. Escape sequence 033
can be used to alter font properties. -e option has to be used in order to the escape sequence be in effect.
Various escape codes are as follows:
 [0m: Normal
 [1m: Bold fonts
 [2m: Font color changes to Purple
 [4m: Underlined fonts
 [7m: Invert foreground and background colors

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 [8m: Invisible fonts
 [9m: Cross lined fonts
 [30m: Font color changes to Grey
 [31m: Font color changes to Red
 [32m: Font color changes to Green
 [33m: Font color changes to Brown
 [34m: Font color changes to Blue
 [35m: Font color changes to Violet
 [36m: Font color changes to Sky Blue
 [37m: Font color changes to Light Grey
 [38m: Font color changes to Black
 [40m: Background color changes to Black

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 [41m: Background color changes to Red
 [42m: Background color changes to Green
 [43m: Background color changes to Brown
 [44m: Background color changes to Blue
 [45m: Background color changes to Violet
 [46m: Background color changes to Sky Blue
 [47m: Background color changes to Light Grey
Example: 1
echo -e "033[31mHello Visitor033[0m"
The above command would print "Hello Visitor" in red color.
Example: 2
echo -e "033[1m033[41mHello Visitor033[0m"
The above command would print "Hello Visitor" in bold style and red background color.
Example 1
Display a string on standard output.
[eleiss@eleiss ~]$ echo "Eleiss Linux Resources"
Eleiss Linux Resources
[eleiss@eleiss ~]$

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Echo prints the string given as argument on standard output.
Example 2
Demonstrate escape sequences in echo command.
[eleiss@eleiss ~]$ echo -e "EleissvLinuxvResources"
Eleiss
Linux
Resources
[eleiss@eleiss ~]$
Escape sequences can be used to format the output on standard output.
Example 3
Print a variable's value on standard output using echo command.
[eleiss@eleiss ~]$ os=Linux
[eleiss@eleiss ~]$ echo "I use $os"
I use Linux
[eleiss@eleiss ~]$
A variable "OS" has been assigned value "Linux" which is accessed by preceding a "$" sign to the
variable name.
Example 4
Testing echo command ( To be deleted )
[nicks@patroclus ~]$ echo "time pass"
time pass
[nicks@patroclus ~]$
This is a time pass example. Do not forget to delete it.
printf
Format and print data
Syntax
printf FORMAT [ARGUMENT]...
printf OPTION
Description
Print ARGUMENT(s) according to FORMAT, or execute according to OPTION
Options
--help Display help and exit

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Format
FORMAT controls the output as in C printf. Interpreted sequences are:
" double quote
backslash
a alert (BEL)
b backspace
c produce no further output
e escape
f form feed
n new line
r carriage return
t horizontal tab
v vertical tab
NNN byte with octal value NNN (1 to 3 digits)
xHH byte with hexadecimal value HH (1 to 2 digits)
uHHHH Unicode (ISO/IEC 10646) character with hex value HHHH (4 digits)
UHHHHHHHH
Unicode character qwith hex value HHHHHHHH (8 digits)
%% a single %
%b ARGUMENT as a string with `' escapes interpreted, except that
octal escapes are of the form 0 or 0NNN
and all C format specifications ending with one of diouxXfeEgGcs, with ARGUMENTs converted to proper
type first. Variable widths are handled.
Example 1
Print a string on standard output using printf command.
[eleiss@eleiss ~]$ printf "EleissvLinuxvResourcesn"
Eleiss
Linux
Resources
[eleiss@eleiss ~]$
[eleiss@eleiss ~]$ printf "Eleiss"
Eleiss[eleiss@eleiss ~]$

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The first command demonstrates printf command with escape sequences and the second command
does that without the sequences.
Example 2
Demonstrate printf command like printf function in C language.
[eleiss@eleiss ~]$ printf "Ten in Decimal is: %dnTen in Octal is: %onTen in
Hexadecimal is: %x n"; 10 10 10
Ten in Decimal is: 10
Ten in Octal is: 12
Ten in Hexadecimal is: a
[eleiss@eleiss ~]$
Format specifiers can be used with printf command in the same way as in "printf" function in C
programming language.
passwd
update user's authentication tokens
Syntax
passwd [-k] [-l] [-u [-f]] [-d] [-n mindays] [-x maxdays] [-w warndays] [-i
inactivedays] [-S] [--stdin] [username]
Description
The passwd utility is used to update user's authentication token(s)
Options
-k The option -k, is used to indicate that the update should only be for expired authentication tokens
(passwords); the user wishes to keep their non-expired tokens as before.
-l This option is used to lock the specified account and it is available to root only. The locking is
performed by rendering the encrypted password into an invalid string (by prefixing the
encrypted string with an !).
--stdin
This option is used to indicate that passwd should read the new password from standard input, which
can be a pipe.
-u This is the reverse of the -l option - it will unlock the account password by removing the ! prefix. This
option is available to root only. By default passwd will refuse to create a passwordless account (it will not
unlock an account that has only "!" as a password). The force option -f will override this
protection.
-d This is a quick way to delete a password for an account. It will set the named account passwordless.
Available to root only.
-n This will set the minimum password lifetime, in days, if the user’s account supports password
lifetimes. Available to root only.

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-x This will set the maximum password lifetime, in days, if the user’s account supports password
lifetimes. Available to root only.
-w This will set the number of days in advance the user will begin receiving warnings that her password
will expire, if the user’s account supports password lifetimes. Available to root only.
Example 1
Change user password.
[eleiss@eleiss ~]$ passwd
Changing password for user eleiss.
Changing password for eleiss.
(current) UNIX password:
New password:
BAD PASSWORD: it is based on a dictionary word
New password:
Retype new password:
passwd: all authentication tokens updated successfully.
[eleiss@eleiss ~]$
It does not accept weak passwords which are short in length or based on a dictionary word.
who
Show who is logged on
Syntax
who [OPTION]... [ FILE | ARG1 ARG2 ]
Description
Print information about users who are currently logged in.
Options
-a, --all
same as -b -d --login -p -r -t -T -u
-b, --boot
time of last system boot
-H, --heading
print line of column headings
-l, --login
print system login processes
-m only hostname and user associated with stdin
-q, --count

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all login names and number of users logged on
-r, --runlevel
print current runlevel
-s, --short
print only name, line, and time (default)
-u, --users
list users logged in
Example 1
Show the name of the users who have currently logged in.
[eleiss@eleiss ~]$ who
eleiss tty1 2011-09-11 12:30 (:0)
eleiss pts/0 2011-09-11 12:32 (:0.0)
jennifer pts/2 2011-09-11 12:40 (:0.0)
eleiss pts/3 2011-09-11 12:42 (192.168.0.89)
alizee pts/4 2011-09-11 12:46 (:0.0)
[eleiss@eleiss ~]$
This command gives a four column output.
1. username
2. Terminal where the user has logged on
3. Log in time
4. IP Address from where the user has connected
Value (0:0) tells that the corresponding user has logged in from the current machine on a graphical
session running on the same machine.
Example 2
Show the last system boot up time using who command.
[eleiss@eleiss ~]$ who -b
system boot 2011-09-11 12:25
[eleiss@eleiss ~]$
The system was boot up on 11 September, 2011 at 12:25 Hours.
w
Show who is logged on and what they are doing
Syntax
w - [husfV] [user]

17 | P a g e
Description
w displays information about the users currently on the machine, and their processes. The header shows,
in this order, the current time, how long the system has been running, how many users are currently
logged on, and the system load averages for the past 1, 5, and 15 minutes.
The following entries are displayed for each user:
login name, the tty name, the remote host, login time, idle time, JCPU, PCPU, and the command line of
their current process.
The JCPU time is the time used by all processes attached to the tty. It does not include past background
jobs, but does include currently running background jobs.
The PCPU time is the time used by the current process, named in the "what" field.
Options
-h Don’t print the header.
-u Ignores the username while figuring out the current process and cpu times. To demonstrate this, do a
"su" and do a "w" and a "w -u".
-s Use the short format. Don’t print the login time, JCPU or PCPU times.
-f Toggle printing the from (remote hostname) field. The default as released is for the from field to not be
printed, although your system administrator or distribution maintainer may have compiled a version in
which the from field is shown by default.
Example 1
Show the name of the users currently logged in the system.
[eleiss@eleiss ~]$ w
12:58:53 up 33 min, 4 users, load average: 0.28, 0.44, 0.49
USER TTY FROM LOGIN@ IDLE JCPU PCPU WHAT
panther tty1 :0 12:30 33:28 60.53s 0.09s pam: gdm-
password
eleiss pts/0 :0.0 12:32 6:52 0.89s 3.75s gnome-
terminal
godfred pts/2 :0.0 12:40 2:16 0.53s 0.22s ssh
eleiss@192.168.0.67
python pts/3 :0.0 12:46 0.00s 0.68s 3.75s gnome-
terminal
[eleiss@eleiss ~]$
The output is same as described above in "Description" section.
The very first row tells about the system boot up time, uptime, total number of currently logged in users,
and system load averages.
1. All the users have logged in from local host on tty1, pts/0, pts/2 and pts/3 respectively.

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2. According to the fourth column, the login time of panther, eleiss, godfred and python are 12:30,
12:32, 12:40 and 12:46 respectively.
3. According to the fifth column, the users are idle for last 33, 6:52, 2:16 and 0 minutes respectively.
4. The last column says what the users are currently doing on their terminal. Panther user has
initiated a graphical session. eleiss and python are running gnome-terminal. While godfred has
made an ssh connection to a host 192.168.0.67 and the user name is eleiss.
uname
Print system information
Syntax
uname [OPTION]...
Description
Print certain system information.
Options
-a, --all
print all information, in the following order, except omit -p and -i if unknown:
-s, --kernel-name
print the kernel name
-n, --nodename
print the network node hostname
-r, --kernel-release
print the kernel release
-v, --kernel-version
print the kernel version
-m, --machine
print the machine hardware name
-p, --processor
print the processor type or "unknown"
-i, --hardware-platform
print the hardware platform or "unknown"
-o, --operating-system
print the operating system
Example 1
Demonstrate uname command.

19 | P a g e
[eleiss@eleiss ~]$ uname -s
Linux
[eleiss@eleiss ~]$ uname -n
eleiss
[eleiss@eleiss ~]$ uname -r
2.6.34.7-63.i686.PAE
[eleiss@eleiss ~]$ uname -v
#1 SMP Fri Dec 3 12:28:58 UTC 2010
[eleiss@eleiss ~]$ uname -m
i686
[eleiss@eleiss ~]$ uname -p
i686
[eleiss@eleiss ~]$ uname -i
i386
[eleiss@eleiss ~]$ uname -o
GNU/Linux
[eleiss@eleiss ~]$ uname -a
Linux eleiss 2.6.34.7-63.i686.PAE #1 SMP Fri Dec 3 12:28:58 UTC 2010 i686
i686 i386 GNU/Linux
[eleiss@eleiss ~]$
The above example demonstrates the use of uname command.
In the output, the last command displays all the information with the help of -a option. The information is
as below:
1. Kernel Name: Linux
2. Hostname of the network node: eleiss
3. Kernel Release: 2.6.34.7-63.i686.PAE
4. Kernel Version: #1 SMP Fri Dec 3 12:28:58 UTC 2010
5. Machine Hardware: i686
6. Processor Type: i686
7. Hardware Platform: i386
8. Operating System: GNU/Linux
expr
Evaluate expressions
Syntax
expr EXPRESSION
expr OPTION
Description
Print the value of EXPRESSION to standard output.
Options
--help display help and exit

20 | P a g e
Expressions
ARG1 | ARG2
ARG1 if it is neither null nor 0, otherwise ARG2
ARG1 & ARG2
ARG1 if neither argument is null or 0, otherwise 0
ARG1 < ARG2
ARG1 is less than ARG2
ARG1 <= ARG2
ARG1 is less than or equal to ARG2
ARG1 = ARG2
ARG1 is equal to ARG2
ARG1 != ARG2
ARG1 is unequal to ARG2
ARG1 >= ARG2
ARG1 is greater than or equal to ARG2
ARG1 > ARG2
ARG1 is greater than ARG2
ARG1 + ARG2
arithmetic sum of ARG1 and ARG2
ARG1 - ARG2
arithmetic difference of ARG1 and ARG2
ARG1 * ARG2
arithmetic product of ARG1 and ARG2
ARG1 / ARG2
arithmetic quotient of ARG1 divided by ARG2
ARG1 % ARG2
arithmetic remainder of ARG1 divided by ARG2
STRING : REGEXP
anchored pattern match of REGEXP in STRING
match STRING REGEXP
same as STRING : REGEXP
substr STRING POS LENGTH
substring of STRING, POS counted from 1
index STRING CHARS
index in STRING where any CHARS is found, or 0
length STRING
length of STRING

21 | P a g e
+ TOKEN
interpret TOKEN as a string, even if it is a keyword like ‘match’ or an operator like ‘/’
( EXPRESSION )
value of EXPRESSION
Example 1
Demonstrate simple mathematical operations in expr command.
[eleiss@eleiss ~]$ expr 10 + 10
20
[eleiss@eleiss ~]$ expr 10 / 10
1
[eleiss@eleiss ~]$ expr 10 - 10
0
[eleiss@eleiss ~]$ expr 10 * 10
100
[eleiss@eleiss ~]$ expr 21 % 10
1
[eleiss@eleiss ~]$
The above example demonstrates how addition, subtraction, multiplication, division and modulation can
be performed by expr command.
You can perform these operation by using the standard operator symbol. But while using multiplication
operator, do not forget to escape the "*" otherwise it will throw a syntax error. This is so because the shell
treat the symbol as a pattern matching character.
Example 2
Can expr command perform mathematical operations on float numbers ?
[eleiss@eleiss ~]$ expr 10 / 3
3
[eleiss@eleiss ~]$ expr 10.5 + 0.5
expr: non-numeric argument
[eleiss@eleiss ~]$
You can not perform operations on float numbers. As you can see in the output, the first command of
division operation returns the floor value of the float number. The second command throws an error.
expr command treats float numbers as strings.
To perform floating point operations, one can use bc command.
Example 3
How can we perform logical expressions with expr command ?
[eleiss@eleiss ~]$ expr 10 > 5
1
[eleiss@eleiss ~]$ expr 10 > 25

22 | P a g e
0
[eleiss@eleiss ~]$ expr 10 < 25
1
[eleiss@eleiss ~]$ expr 10 < 2
0
[eleiss@eleiss ~]$ expr 10 = 2
0
[eleiss@eleiss ~]$ expr 10 = 10
1
[eleiss@eleiss ~]$ expr 10 != 10
0
[eleiss@eleiss ~]$ expr 10 != 20
1
[eleiss@eleiss ~]$
The output is self explanatory. When the expression is true, the command displays 0 or else it displays 1.
Do not forget to escape the operator symbols.
Example 4
How to match regular expression using expr command ?
[eleiss@eleiss ~]$ expr "I love Linux" : Î.*love$
6
[eleiss@eleiss ~]$ expr "I love Linux" : Î.*L.*$
12
[eleiss@eleiss ~]$ expr "I love Linux" : Î.*do not.*$
0
[eleiss@eleiss ~]$ expr match "browser-v4.1-os" ^browser.*-os$
15
[eleiss@eleiss ~]$ expr match "browser-v4.1-os" ^rowser.*-os$
0
[eleiss@eleiss ~]$
If the string does not match the regular expression, the command returns 0.
Else the total number of characters that match the regular expression.
Example 5
Extract a part of string (substring) from a string using expr command.
[eleiss@eleiss ~]$ expr substr computer 2 5
omput
[eleiss@eleiss ~]$
The command extracts a substring starting at position 2 and length of 5 characters from the string
"computer;"
Example 6
Calculate length of a string using expr command.

23 | P a g e
[eleiss@eleiss ~]$ expr length "Count the length of this string"
31
[eleiss@eleiss ~]$
expr prints the length of the given string when length is used with the command.
Example 7
Find the first position of a character in the given string using expr command.
[eleiss@eleiss ~]$ expr index "Where is n in this string ?" n
10
[eleiss@eleiss ~]$
expr prints the first position of a character in the given string when index is used with the command.
test
Check file types and compare values
Syntax
test EXPRESSION
test
[ EXPRESSION ]
[ ]
[ OPTION
Description
Exit with the status determined by EXPRESSION. An omitted EXPRESSION defaults to false. Otherwise,
EXPRESSION is true or false and sets exit status.
Options
--help display help and exit
Expessions
( EXPRESSION )
EXPRESSION is true
! EXPRESSION
EXPRESSION is false
EXPRESSION1 -a EXPRESSION2
both EXPRESSION1 and EXPRESSION2 are true
EXPRESSION1 -o EXPRESSION2
either EXPRESSION1 or EXPRESSION2 is true

24 | P a g e
-n STRING
the length of STRING is nonzero
STRING equivalent to -n STRING
-z STRING
the length of STRING is zero
STRING1 = STRING2
the strings are equal
STRING1 != STRING2
the strings are not equal
INTEGER1 -eq INTEGER2
INTEGER1 is equal to INTEGER2
INTEGER1 -ge INTEGER2
INTEGER1 is greater than or equal to INTEGER2
INTEGER1 -gt INTEGER2
INTEGER1 is greater than INTEGER2
INTEGER1 -le INTEGER2
INTEGER1 is less than or equal to INTEGER2
INTEGER1 -lt INTEGER2
INTEGER1 is less than INTEGER2
INTEGER1 -ne INTEGER2
INTEGER1 is not equal to INTEGER2
FILE1 -ef FILE2
FILE1 and FILE2 have the same device and inode numbers
FILE1 -nt FILE2
FILE1 is newer (modification date) than FILE2
FILE1 -ot FILE2
FILE1 is older than FILE2
-b FILE
FILE exists and is block special
-c FILE
FILE exists and is character special
-d FILE
FILE exists and is a directory
-e FILE
FILE exists
-f FILE
FILE exists and is a regular file

25 | P a g e
-g FILE
FILE exists and is set-group-ID
-G FILE
FILE exists and is owned by the effective group ID
-h FILE
FILE exists and is a symbolic link (same as -L)
-k FILE
FILE exists and has its sticky bit set
-L FILE
FILE exists and is a symbolic link (same as -h)
-O FILE
FILE exists and is owned by the effective user ID
-p FILE
FILE exists and is a named pipe
-r FILE
FILE exists and read permission is granted
-s FILE
FILE exists and has a size greater than zero
-S FILE
FILE exists and is a socket
-t FD file descriptor FD is opened on a terminal
-u FILE
FILE exists and its set-user-ID bit is set
-w FILE
FILE exists and write permission is granted
-x FILE
FILE exists and execute (or search) permission is granted
Example 1
Check if length of given string is non-zero.
[eleiss@eleiss ~]$ test -n "Learning Linux commands is very easy"
[eleiss@eleiss ~]$ echo $?
0
[eleiss@eleiss ~]$ test -n ""
1
[eleiss@eleiss ~]$
test command does not print anything. That is why it is very much useful in shell scripts for condition
testing.

26 | P a g e
In the above example, output status "0" indicates that the length of the provided string is non-zero. If the
status is "1" then the length of the string is zero. i.e an empty string is supplied.
Example 2
Check if length of given string is zero.
[eleiss@eleiss ~]$ test -z "Learning Linux commands is very easy"
1
[eleiss@eleiss ~]$ test -z ""
0
[eleiss@eleiss ~]$
In the above example, output status "1" indicates that the length of the provided string is zero. If the status
is "0" then the length of the string is zero. i.e an empty string is supplied.
Example 3
Demonstrate how to match two strings using test command.
[eleiss@eleiss ~]$ test "India" = "India"
0
[eleiss@eleiss ~]$ test "India" = "india"
1
[eleiss@eleiss ~]$ test "Unix" != "Unix"
1
[eleiss@eleiss ~]$ test "Unix" != "unix"
0
[eleiss@eleiss ~]$
As we already know that test command does not print anything on standard output. If the status of the
command is "0" then the expression evaluated is true and if the status of the command is "1" then the
expression evaluated is false.
Unlike, other popular programming languages, test command does not need to supply "=" operator two
times
Do not get confused with the assignment operator and this string matching operator of test
command.
Example 4
Demonstrate logical expressions for two integer numbers using test command.
[eleiss@eleiss ~]$ test 5 -eq 5
0

27 | P a g e
[eleiss@eleiss ~]$ test 5 -ge 5
0
[eleiss@eleiss ~]$ test 5 -gt 5
1
[eleiss@eleiss ~]$ test 5 -lt 5
1
[eleiss@eleiss ~]$ test 5 -le 5
0
[eleiss@eleiss ~]$ test 5 -ne 5
1
[eleiss@eleiss ~]$
The meaning of the operators used in this example is as below:
1. -eq: Compare two operands for equality
2. -ne: Opposite of -eq
3. -gt: Check if the first operand is greater than the second operand
4. -ge: Check if the first operand is greater than or equal to second operand
5. -lt: Check if the first operand is less than the second operand
6. -le: Check if the first operand is less than or equal to second operand
Example 5
Check if a given file exists and is a regular file using test command.
[eleiss@eleiss ~]$ test -f out.ogv
0
[eleiss@eleiss ~]$ ls -l out.ogv
-rw-rw-r--. 1 eleiss eleiss 24539234 Aug 12 2010 out.ogv
[eleiss@eleiss ~]$
In this example you can see in the output of ls command that "out.ogv" is a regular file and of course it
does exist.
Example 6
Check if a given file has read permission.
[eleiss@eleiss ~]$ test -r out.ogv
0
[eleiss@eleiss ~]$ ls -l out.ogv
[eleiss@eleiss ~]$ test -r /etc/shadow
1

28 | P a g e
[eleiss@eleiss ~]$ ls -l /etc/shadow
----------. 1 root root 1683 Jul 31 04:02 /etc/shadow
[eleiss@eleiss ~]$
In the output you can see, that "out.ogv" file has read permission for the user. But "/etc/shadow" does not
have.
seq
Print a sequence of numbers
Syntax
seq [OPTION]... LAST
seq [OPTION]... FIRST LAST
seq [OPTION]... FIRST INCREMENT LAST
Description
Print numbers from FIRST to LAST, in steps of INCREMENT. If FIRST or INCREMENT is omitted, it
defaults to 1.
Options
-f, --format=FORMAT
use printf style floating-point FORMAT
-s, --separator=STRING
use STRING to separate numbers (default: n)
-w, --equal-width
equalize width by padding with leading zeroes
Example 1
Print a sequence of numbers starting from 1 to 10.
[eleiss@eleiss ~]$ seq 1 10
1
2
3
4
5
6
7
8
9
10
[eleiss@eleiss ~]$
This command is very useful in shell scripts for looping purpose.

29 | P a g e
Example 2
Print first 10 odd numbers.
[eleiss@eleiss ~]$ seq 1 2 20
1
3
5
7
9
11
13
15
17
19
[eleiss@eleiss ~]$
The middle digit is the increment value for the sequence starting from 1 to 20 which results into first ten
odd numbers.
factor
Factor numbers
Syntax
factor [NUMBER]...
factor OPTION
Description
Print the prime factors of each specified integer NUMBER. If none are specified on the command line,
read them from standard input.
Options
--help display this help and exit
Example 1
Find prime factors of a given number.
[eleiss@eleiss ~]$ factor 100
100: 2 2 5 5
[eleiss@eleiss ~]$
This example finds the factor of 100.
rev
reverse lines of a file or files

30 | P a g e
Syntax
rev [file ...]
Description
The rev utility copies the specified files to the standard output, reversing the order of characters in every
line. If no files are specified, the standard input is read.
Options
No options available.
Filesystem Navigation
1. pwd - print name of current/working/present directory
2. cd - Change the current directory
3. mkdir - make directories
4. rmdir - remove empty directories
5. ls - list directory contents
pwd
print name of current/working/present directory
Syntax
pwd [OPTION]...
Description
Print the full filename of the current working directory.
Options
-L, --logical
use PWD from environment, even if it contains symlinks
-P, --physical
avoid all symlinks
Example 1
Display the present working directory.
[eleiss@eleiss ~]$ pwd
/home/eleiss
Here /home/eleiss is the present working directory.

31 | P a g e
In other words absolute path of "." directory
cd
Change the current directory
Syntax
cd [-L|-P] [dir]
Description
Change the current directory to dir. The variable HOME is the default dir. The variable CDPATH defines
the search path for the directory containing dir. Alternative directory names in CDPATH are separated by
a colon (:). A null directory name in CDPATH is the same as the current directory, i.e., ‘‘.’’. If dir begins
with a slash (/), then CDPATH is not used. An argument of - is equivalent to $OLDPWD. If a non-empty
directory name from CDPATH is used, or if - is the first argument, and the directory change is successful,
the absolute pathname of the new working directory is written to the standard output. The return value is
true if the directory was successfully changed; false otherwise.
Options
-P option to the set builtin command
-L option forces symbolic links to be followed
Example 1
Demonstration of cd command
[eleiss@eleiss ~]$ pwd
/home/eleiss
[eleiss@eleiss ~]$ cd Documents/
[eleiss@eleiss Documents]$ pwd
/home/eleiss/Documents
[eleiss@eleiss Documents]$ cd /etc
[eleiss@eleiss etc]$ pwd
/etc
[eleiss@eleiss etc]$
The first time pwd says that the working directory was "/home/eleiss". Running cd Documents changes
our current directory to "/home/eleiss/Documents."
Later is the example of cd command with absolute pathname.
mkdir
make directories
Syntax

32 | P a g e
mkdir [OPTION]... DIRECTORY...
Description
Create the DIRECTORY(ies), if they do not already exist.
Options
-m, --mode=MODE
set file mode (as in chmod), not a=rwx - umask
-p, --parents
no error if existing, make parent directories as needed
-v, --verbose
print a message for each created directory
Example 1
Create a directory named Linux in current directory.
[eleiss@eleiss empty]$ mkdir -v linux
mkdir: created directory `linux'
[eleiss@eleiss empty]$ ls
linux
[eleiss@eleiss empty]$
The above creates "Linux" directory in current directory. -v option prints the output.
Example 2
Create multiple directories in a single command.
[eleiss@eleiss empty]$ mkdir -v city state country
mkdir: created directory `city'
mkdir: created directory `state'
mkdir: created directory `country'
city country linux state
More than one directories can be created in a single mkdir command by providing all the names to the
command.
Example 3
Create a directory hierarchy.
[eleiss@eleiss empty]$ mkdir -v friends friends/jigi friends/sachi
friends/het friends/daiv
mkdir: created directory `friends'
mkdir: created directory `friends/jigi'

33 | P a g e
mkdir: created directory `friends/sachi'
mkdir: created directory `friends/het'
mkdir: created directory `friends/daiv'
[eleiss@eleiss empty]$ ls friends/
daiv het jigi sachi
[eleiss@eleiss empty]$ mkdir -v fruits/mango fruits/orange fruits
mkdir: cannot create directory `fruits/mango': No such file or directory
mkdir: cannot create directory `fruits/orange': No such file or directory
mkdir: created directory `fruits'
[eleiss@eleiss empty]$ ls fruits/
To create a parent-child directory hierarchy, provide parent directory first followed by children directories.
Example 4
Create a directory hierarchy (better way).
[eleiss@eleiss empty]$ mkdir -pv tree/branches/leaves
mkdir: created directory `tree'
mkdir: created directory `tree/branches'
mkdir: created directory `tree/branches/leaves'
To create a parent-child directory hierarchy in a better way, one should use -p option. Provide the
directory hierarchy as an argument.
rmdir
remove empty directories
Syntax
rmdir [OPTION]... DIRECTORY...
Description
Remove the DIRECTORY(ies), if they are empty.
Options
--ignore-fail-on-non-empty
ignore each failure that is solely because a directory is non-empty
-p, --parents
remove DIRECTORY and its ancestors; e.g., ‘rmdir -p a/b/c’ is similar to ‘rmdir a/b/c a/b a’
-v, --verbose
output a diagnostic for every directory processed
Example 1

34 | P a g e
Remove a directory in current directory.
city country friends fruits linux state tree
[eleiss@eleiss empty]$ rmdir -v city
rmdir: removing directory, `city'
country friends fruits linux state tree
[eleiss@eleiss empty]$ rmdir friends
rmdir: failed to remove `friends': Directory not empty
Provide the directory name (absolute or relative path) to rmdir as an argument in order to remove it.
If the directory is not empty, then the command will throw an error.
Example 2
Remove a directory hierarchy.
[eleiss@eleiss empty]$ rmdir -pv tree/branches/leaves/
rmdir: removing directory, `tree/branches/leaves/'
rmdir: removing directory, `tree/branches'
rmdir: removing directory, `tree'
We can remove a directory hierarchy using -p option. The innermost directory gets removed first and then
the outer one and so forth.
ls
list directory contents
Syntax
ls [OPTION]... [FILE]...
Description
List information about the FILEs (the current directory by default). Sort entries alphabetically if none of -
cftuvSUX nor --sort.
Options
-a, --all
do not ignore entries starting with .
-A, --almost-all
do not list implied . and ..
-c with -lt: sort by, and show, ctime (time of last modification of file status information) with -l: show
ctime and sort by name otherwise: sort by ctime

35 | P a g e
-C list entries by columns
--color[=WHEN]
control whether color is used to distinguish file types. WHEN may be ‘never’, ‘always’, or ‘auto’
-d, --directory
list directory entries instead of contents, and do not dereference symbolic links
--group-directories-first
group directories before files. augment with a --sort option, but any use of --sort=none (-U)
disables grouping
-h, --human-readable
with -l, print sizes in human readable format (e.g., 1K 234M 2G)
--si likewise, but use powers of 1000 not 1024
-H, --dereference-command-line
follow symbolic links listed on the command line
--dereference-command-line-symlink-to-dir
follow each command line symbolic link that points to a directory
-i, --inode
print the index number of each file
-I, --ignore=PATTERN
do not list implied entries matching shell PATTERN
-l use a long listing format
-L, --dereference
when showing file information for a symbolic link, show information for the file the link references
rather than for the link itself
-n, --numeric-uid-gid
like -l, but list numeric user and group IDs
-r, --reverse
reverse order while sorting
-R, --recursive
list subdirectories recursively
-S sort by file size
--time-style=STYLE
with -l, show times using style STYLE: full-iso, long-iso, iso, locale, +FORMAT. FORMAT is
interpreted like ‘date’; if FORMAT is FORMAT1<newline>FORMAT2, FORMAT1 applies to non-
recent files and FORMAT2 to recent files; if STYLE is prefixed with ‘posix-’, STYLE takes effect only
outside the POSIX locale
-t sort by modification time

36 | P a g e
-u with -lt: sort by, and show, access time with -l: show access time and sort by name otherwise: sort
by access time
-U do not sort; list entries in directory order
-v natural sort of (version) numbers within text
-x list entries by lines instead of by columns
-X sort alphabetically by entry extension
-1 list one file per line
Example 1
List the content of a directory
country friends fruits guitar linux state
[eleiss@eleiss empty]$ ls .
country friends fruits guitar linux state
[eleiss@eleiss empty]$ ls friends/
daiv het jigi sachi
[eleiss@eleiss empty]$ ls /usr/
bin etc games include kerberos lib libexec local sbin share src
tmp
When we run ls command without any options, it lists the files and directory of the current directory.
We can provide an absolute or relative path as well as an argument.
Example 2
List all the files and directories including the hidden ones.
[eleiss@eleiss empty]$ ls -a
. .. country friends fruits guitar .hidden linux state
When ls command is run with -a option the hidden files and directories are also listed.
In the above output, ., .. and .hidden are hidden ones.
Example 3
Long listing /usr directory.
[eleiss@eleiss empty]$ ls -l /usr/
total 336
dr-xr-xr-x. 2 root root 106496 Sep 1 12:46 bin
drwxr-xr-x. 2 root root 4096 Oct 1 2009 etc
drwxr-xr-x. 2 root root 4096 Oct 1 2009 games

37 | P a g e
drwxr-xr-x. 177 root root 20480 Jun 29 19:54 include
drwxr-xr-x. 6 root root 4096 Dec 1 2010 kerberos
dr-xr-xr-x. 227 root root 143360 Jul 28 12:39 lib
drwxr-xr-x. 39 root root 12288 Jul 8 00:33 libexec
drwxr-xr-x. 12 root root 4096 Oct 28 2010 local
dr-xr-xr-x. 2 root root 20480 Aug 2 10:35 sbin
drwxr-xr-x. 391 root root 12288 Jul 28 12:39 share
drwxr-xr-x. 5 root root 4096 Nov 13 2010 src
lrwxrwxrwx. 1 root root 10 Jul 15 2010 tmp -> ../var/tmp
The very first row is the total number of filesystem blocks occupied by the particular directory.
The remaining is a 9 field output. These fields are separated by one or multiple white spaces. These
fields are as:
1. File type and permissions
First character indicates file type.
o d : Directory
o - : Regular File
o p : FIFO File
o s : Socket File
o b : Block Special File
o c : Character Special File
o l : Symbolic Link
Permissions include Read, Write and Execute permission bits for owner, group and others.
2. Number of hardlinks
3. Owner
4. Group Owner
5. Size in bytes
6. Last Modification Time (Next three fields)
7. Name of files and directories
Example 4
Show the information of a directory but not of the files or directories in it.
[eleiss@eleiss empty]$ ls -ld /usr/
drwxr-xr-x. 13 root root 4096 Jul 15 2010 /usr/
[eleiss@eleiss empty]$ ls -l /usr/
total 336
dr-xr-xr-x. 2 root root 106496 Sep 1 12:46 bin
drwxr-xr-x. 2 root root 4096 Oct 1 2009 etc
drwxr-xr-x. 2 root root 4096 Oct 1 2009 games
drwxr-xr-x. 177 root root 20480 Jun 29 19:54 include
drwxr-xr-x. 6 root root 4096 Dec 1 2010 kerberos

38 | P a g e
dr-xr-xr-x. 227 root root 143360 Jul 28 12:39 lib
drwxr-xr-x. 39 root root 12288 Jul 8 00:33 libexec
drwxr-xr-x. 12 root root 4096 Oct 28 2010 local
dr-xr-xr-x. 2 root root 20480 Aug 2 10:35 sbin
drwxr-xr-x. 391 root root 12288 Jul 28 12:39 share
drwxr-xr-x. 5 root root 4096 Nov 13 2010 src
lrwxrwxrwx. 1 root root 10 Jul 15 2010 tmp -> ../var/tmp
-d option does not list the content of the given directory. Rather the command shows the information of
the directory itself.
Example 5
Show the i-node number of all the files and directory in the given directory.
[eleiss@eleiss empty]$ ls -i
647399 country 647405 fruits 647396 linux
647400 friends 647397 guitar 647398 state
-i option with ls command lists the content of a directory with their respective i-node numbers
File and Directory Operations
1. cat - concatenate files and print on the standard output
2. touch - change file timestamps
3. cp - copy files and directories
4. rm - remove files or directories
5. mv - move (rename) files
6. more - file perusal filter for crt viewing
7. file - determine file type
8. wc - print newline, word, and byte counts for each file
9. od - dump files in octal and other formats
10. cmp - compare two files
11. comm - compare two sorted files line by line
12. diff - find differences between two files
cat
concatenate files and print on the standard output
Syntax
cat [OPTION]... [FILE]...
Description
Concatenate FILE(s), or standard input, to standard output.

39 | P a g e
Options
-b, --number-nonblank
number nonempty output lines
-E, --show-ends
display $ at end of each line
-s, --squeeze-blank
suppress repeated empty output lines
-T, --show-tabs
display TAB characters as ^I
-v, --show-nonprinting
use ^ and M- notation, except for LFD and TAB
Example 1
Display content of a file to standard output.
[eleiss@eleiss ~]$ cat india
India is a great country. Jai Hind.
[eleiss@eleiss ~]$
The command reads the content of a file given as an argument and prints on standard output.
Example 2
Read content of multiple files and print to standard output.
[eleiss@eleiss ~]$ cat quote
most debugging problems are fixed easily; identifying the location of the
problem is hard
[eleiss@eleiss ~]$ cat /etc/shells
/bin/sh
/bin/bash
/sbin/nologin
/bin/tcsh
/bin/csh
/bin/zsh
[eleiss@eleiss ~]$ cat quote /etc/shells
most debugging problems are fixed easily; identifying the location of the
problem is hard
/bin/sh
/bin/bash
/sbin/nologin
/bin/tcsh
/bin/csh
/bin/zsh
[eleiss@eleiss ~]$
It is simple. Just keep on writing all the file names you want to read. The content of all the files get
displayed on standard output.

40 | P a g e
Example 3
Create a file using cat command.
[eleiss@eleiss ~]$ cat > computer
Computer is not as much intelligent as the human brain is.
[eleiss@eleiss ~]$ cat computer
[eleiss@eleiss ~]$
Using the > symbol, we can redirect the standard output to a file resulting in creation of a new file. Press
Ctrl + d when content to the file is over.
Example 4
Append to a file using cat command.
[eleiss@eleiss ~]$ cat >> computer
Not even a supercomputer is.
[eleiss@eleiss ~]$
Appending to a file is another purpose of cat command.
Example 5
Copy a file using cat command.
[eleiss@eleiss ~]$ cat india > country
[eleiss@eleiss ~]$ cat country
[eleiss@eleiss ~]$
File before > symbol is source file and file after > symbol is the destination file. If the destination file does
not exist, then a new file is created. If destination file already exists, then it is truncated before copying.
Example 6
Concatenate two files
[eleiss@eleiss ~]$ cat india computer >> newfile
[eleiss@eleiss ~]$ cat newfile

41 | P a g e
[eleiss@eleiss ~]$
In the above command the two files "computer" and "india" are concatenated into a new file "newfile"
touch
change file timestamps
Syntax
touch [OPTION]... FILE...
Description
Update the access and modification times of each FILE to the current time. A FILE argument that does
not exist is created empty. A FILE argument string of - is handled specially and causes touch to change
the times of the file associated with standard output.
Options
-a change only the access time
-c, --no-create
do not create any files
-d, --date=STRING
parse STRING and use it instead of current time
-m change only the modification time
-r, --reference=FILE
use this file’s times instead of current time
-t STAMP
use [[CC]YY]MMDDhhmm[.ss] instead of current time
--time=WORD
change the specified time: WORD is access, atime, or use: equivalent to -a WORD is modify or
mtime: equivalent to -m
Date String
The --date=STRING is a mostly free format human readable date string such as "Sun, 29 Feb 2004
16:21:42 -0800" or "2004-02-29 16:21:42" or even "next Thursday". A date string may contain items
indicating calendar date, time of day, time zone, day of week, relative time, relative date, and numbers.
An empty string indicates the beginning of the day. The date string format is more complex than is easily
documented here but is fully described in the info documentation.
Example 1

42 | P a g e
Create a new file using touch command.
[eleiss@eleiss ~]$ touch hexagon
[eleiss@eleiss ~]$ ls -l hexagon
-rw-rw-r--. 1 nicks nicks 0 Sep 2 15:35 hexagon
[eleiss@eleiss ~]$ ls -l india
-rw-rw-r--. 1 nicks nicks 36 Sep 2 15:04 india
[eleiss@eleiss ~]$ touch india
[eleiss@eleiss ~]$
If the file does not exist then it is created with zero length. In above command "hexagon" file is a newly
created file with zero length.
If file already exists then its last access time and last modification times are updated. In the above
command, the modification time of the file "india" has been chaged.
Example 2
Change the modification time of a file.
[eleiss@eleiss ~]$ touch -t 201101010000 india
-rw-rw-r--. 1 nicks nicks 36 Jan 1 2011 india
[eleiss@eleiss ~]$
In the above command we can see the last modification time of the file "india" has been changed with the
help of touch command without altering the file content.
This is a hack ! You can alter the last modification time of your work done and claim an earlier
date or time as your completion time ;-)
cp
copy files and directories
Syntax
cp [OPTION]... [-T] SOURCE DEST
cp [OPTION]... SOURCE... DIRECTORY
cp [OPTION]... -t DIRECTORY SOURCE...
Description
Copy SOURCE to DEST, or multiple SOURCE(s) to DIRECTORY.
Options

43 | P a g e
-a, --archive
same as -dR --preserve=all
--backup[=CONTROL]
make a backup of each existing destination file
-d same as --no-dereference --preserve=links
-f, --force
if an existing destination file cannot be opened, remove it and try again (redundant if the -n option is
used)
-i, --interactive
prompt before overwrite (overrides a previous -n option)
-H follow command-line symbolic links in SOURCE
-l, --link
link files instead of copying
-L, --dereference
always follow symbolic links in SOURCE
-P, --no-dereference
never follow symbolic links in SOURCE
-p same as --preserve=mode,ownership,timestamps
-R, -r, --recursive
copy directories recursively
-t, --target-directory=DIRECTORY
copy all SOURCE arguments into DIRECTORY
-T, --no-target-directory
treat DEST as a normal file
-u, --update
copy only when the SOURCE file is newer than the destination file or when the destination file is
missing
-v, --verbose
explain what is being done
Example 1
Copy a file from one directory to another directory.
[eleiss@eleiss ~]$ cp -v /etc/passwd .
`/etc/passwd' -> `./passwd'
[eleiss@eleiss ~]$ ls
passwd
[eleiss@eleiss ~]$ cp -v /etc/passwd ./password
`/etc/passwd' -> `./password'

44 | P a g e
passwd password
[eleiss@eleiss ~]$
Copying a file from one directory to another directory is as simple as providing the source file path and
destination file path. If the destination is a directory then a new file is created with the same name as
source file.
Example 2
Copy entire directory to another location.
[eleiss@eleiss ~]$ ls divya/
file1 file2
[eleiss@eleiss ~]$ cp -vr divya/ kavya
`divya/' -> `kavya'
`divya/file1' -> `kavya/file1'
`divya/file2' -> `kavya/file2'
[eleiss@eleiss ~]$
In the above command, the "divya" directory is copied to "kavya". If the destination directory does not
exist, it is created and then the files are copied into it.
rm
remove files or directories
Syntax
rm [OPTION]... FILE...
Description
rm removes each specified file. By default, it does not remove directories.
Options
-f, --force
ignore nonexistent files, never prompt
-i prompt before every removal
-I prompt once before removing more than three files, or when removing recursively. Less intrusive
than -i, while still giving protection against most mistakes
-r, -R, --recursive
remove directories and their contents recursively
-v, --verbose
explain what is being done
Example 1

45 | P a g e
Remove a file.
[eleiss@eleiss ~]$ rm -v divya/file1
removed `divya/file1'
[eleiss@eleiss ~]$ rm -v divya/
rm: cannot remove `divya/': Is a directory
[eleiss@eleiss ~]$
The above command demonstrates how to remove a file using rm command. We have to provide a
filename as an argument. We can see that by default a directory can not be removed using rm command.
Example 2
Remove a directory using rm command.
[eleiss@eleiss ~]$ rm -vr divya/
removed `divya/file2'
removed directory: `divya'
[eleiss@eleiss ~]$
As we have seen earlier that an empty directory can not be deleted. Using the -r option
with rm command, we can recursively remove a directory. First all the files and subdirectories
(recursively) are removed and then at the end the parent directory gets deleted.
rm command is more flexible than rmdir command.
mv
move (rename) files
Syntax
mv [OPTION]... [-T] SOURCE DEST
mv [OPTION]... SOURCE... DIRECTORY
mv [OPTION]... -t DIRECTORY SOURCE...
Description
Rename SOURCE to DEST, or move SOURCE(s) to DIRECTORY.
Options
-f, --force
do not prompt before overwriting
-i, --interactive
prompt before overwrite
-t, --target-directory=DIRECTORY
move all SOURCE arguments into DIRECTORY
-T, --no-target-directory

46 | P a g e
treat DEST as a normal file
-u, --update
move only when the SOURCE file is newer than the destination file or when the destination file is
missing
Example 1
Move a file from one location to another location.
[eleiss@eleiss ~]$ mv -v /tmp/shell_scripting .
`/tmp/shell_scripting' -> `./shell_scripting'
shell_scripting
[eleiss@eleiss ~]$
The above command moves a file named shell_scripting from /tmp directory to the current directory.
Example 2
Rename a file using mv command.
Mail Unix
[eleiss@eleiss ~]$ mv -v Unix Linux
`Unix' -> `Linux'
Linux Mail
[eleiss@eleiss ~]$
A file or directory can be rename by moving it in the same directory. In this example "Unix" is moved in
the same directory with a new name "Linux"
Searching and Locating
1. updatedb - update a database for mlocate
2. locate - find files by name
3. find - search for files in a directory hierarchy
updatedb
update a database for mlocate
Syntax
updatedb [OPTION]...
Description
updatedb creates or updates a database used by locate(1). If the database already exists, its data is
reused to avoid rereading directories that have not changed.

47 | P a g e
updatedb is usually run daily by cron(8) to update the default database.
Options
-U, --database-root PATH
Store only results of scanning the file system subtree rooted at PATH to the generated database. The
whole file system is scanned by default.
-o, --output FILE
Write the database to FILE instead of using the default database.
-v, --verbose
Output path names of files to standard output, as soon as they are found.
locate
find files by name
Syntax
locate [OPTION]... PATTERN...
Description
locate reads one or more databases prepared by updatedb(8) and writes file names matching at least one
of the PATTERNs to standard output, one per line.
If --regex is not specified, PATTERNs can contain globbing characters. If any PATTERN contains no
globbing characters, locate behaves as if the pattern were *PATTERN*.
By default, locate does not check whether files found in database still exist. locate can never report files
created after the most recent update of the relevant database.
Options
-b, --basename
Match only the base name against the specified patterns. This is the opposite of --wholename.
-c, --count
Instead of writing file names on standard output, write the number of matching entries only.
-d, --database DBPATH
Replace the default database with DBPATH. DBPATH is a :-separated list of database file names. If
more than one --database option is specified, the resulting path is a concatenation of the separate paths.
An empty database file name is replaced by the default database. A database file name - refers to
the standard input. Note that a database can be read from the standard input only once.
-e, --existing
Print only entries that refer to files existing at the time locate is run.
-i, --ignore-case
Ignore case distinctions when matching patterns.

48 | P a g e
-l, --limit, -n LIMIT
Exit successfully after finding LIMIT entries. If the --count option is specified, the resulting count is
also limited to LIMIT.
-r, --regexp REGEXP
Search for a basic regexp REGEXP. No PATTERNs are allowed if this option is used, but this option
can be specified multiple times.
--regex
Interpret all PATTERNs as extended regexps.
Example 1
search for a file using locate command.
[eleiss@eleiss ~]$ locate hello-1.1.c
/home/eleiss/hello-1.1.c
[eleiss@eleiss ~]$
The output is self explaining. The target file is located in /home/eleiss directory.
NOTE: In order to locate newly created files, the database must be updated first
using updatedb command.
find
search for files in a directory hierarchy
Syntax
find [-H] [-L] [-P] [-D debugopts] [-Olevel] [path...] [expression]
Description
find searches the directory tree rooted at each given file name by evaluating the given expression from
left to right, according to the rules of precedence, until the outcome is known (the left hand side is false
for and operations, true for or), at which point find moves on to the next file name.
Options
-P Never follow symbolic links.
-L Follow symbolic links.
When the -L option is in effect, the -type predicate will always match against the type of the file that a
symbolic link points to rather than the link itself (unless the symbolic link is broken). Using -L causes the -
lname and -ilname predicates always to return false.
-H Do not follow symbolic links, except while processing the command line arguments.
-Olevel

49 | P a g e
Enables query optimisation. The find program reorders tests to speed up execution while preserving
the overall effect; that is, predicates with side effects are not reordered relative to each other. The
optimisations performed at each optimisation level are as follows.
0 Equivalent to optimisation level 1.
1 This is the default optimisation level and corresponds to the traditional behaviour. Expressions
are reordered so that tests based only on the names of files (for example -name and -regex) are
performed first.
2 Any -type or -xtype tests are performed after any tests based only on the names of files, but
before any tests that require information from the inode. On many modern versions of Unix, file types are
returned by readdir() and so these predicates are faster to evaluate than predicates which need to stat
the file first.
3 At this optimisation level, the full cost-based query optimiser is enabled. The order of tests is
modified so that cheap (i.e. fast) tests are performed first and more expensive ones are performed later, if
necessary. Within each cost band, predicates are evaluated earlier or later according to whether they are
likely to succeed or not. For -o, predicates which are likely to succeed are evaluated earlier, and for -a,
predicates which are likely to fail are evaluated earlier.
Expressions
-maxdepth levels
Descend at most levels (a non-negative integer) levels of directories below the command line
arguments. -maxdepth 0 means only apply the tests and actions to the command line arguments.
-mindepth levels
Do not apply any tests or actions at levels less than levels (a non-negative integer). -mindepth 1
means process all files except the command line arguments.
-mount Don’t descend directories on other filesystems. An alternate name for -xdev, for compatibility with
some other versions of find.
-noleaf
Do not optimize by assuming that directories contain 2 fewer subdirectories than their hard link count.
-regextype type
Changes the regular expression syntax understood by -regex and -iregex tests which occur later on
the command line.
-xautofs
Don’t descend directories on autofs filesystems.
-xdev Don’t descend directories on other filesystems.
Tests
Numeric arguments can be specified as
+n for greater than n,
-n for less than n,
n for exactly n.

50 | P a g e
-amin n
File was last accessed n minutes ago.
-anewer file
File was last accessed more recently than file was modified.
-atime n
File was last accessed n*24 hours ago.
-cmin n
File’s status was last changed n minutes ago.
-cnewer file
File’s status was last changed more recently than file was modified.
-ctime n
File’s status was last changed n*24 hours ago.
-empty File is empty and is either a regular file or a directory.
-executable
Matches files which are executable and directories which are searchable (in a file name resolution
sense).
-false Always false.
-fstype type
File is on a filesystem of type type.
-gid n File’s numeric group ID is n.
-group gname
File belongs to group gname (numeric group ID allowed).
-iname pattern
Like -name, but the match is case insensitive.
-ipath pattern
Behaves in the same way as -iwholename. This option is deprecated, so please do not use it.
-iregex pattern
Like -regex, but the match is case insensitive.
-links n
File has n links.
-lname pattern
File is a symbolic link whose contents match shell pattern pattern.
-mmin n
File’s data was last modified n minutes ago.
-mtime n
File’s data was last modified n*24 hours ago.

51 | P a g e
-name pattern
Base of file name (the path with the leading directories removed) matches shell pattern pattern.
-newer file
File was modified more recently than file.
-nogroup
No group corresponds to file’s numeric group ID.
-nouser
No user corresponds to file’s numeric user ID.
-path pattern
File name matches shell pattern pattern.
-perm mode
File’s permission bits are exactly mode (octal or symbolic).
-perm -mode
All of the permission bits mode are set for the file.
-perm /mode
Any of the permission bits mode are set for the file.
-perm +mode
Deprecated, old way of searching for files with any of the permission bits in mode set.
-readable
Matches files which are readable.
-regex pattern
File name matches regular expression pattern.
-size n[cwbkMG]
File uses n units of space. The following suffixes can be used:
‘b’ for 512-byte blocks (this is the default if no suffix is used)
‘c’ for bytes
‘w’ for two-byte words
‘k’ for Kilobytes (units of 1024 bytes)
‘M’ for Megabytes (units of 1048576 bytes)
‘G’ for Gigabytes (units of 1073741824 bytes)
-type c
File is of type c:
b block (buffered) special
c character (unbuffered) special
d directory

52 | P a g e
p named pipe (FIFO)
f regular file
l symbolic link; this is never true if the -L option or the -follow option is in effect, unless the
symbolic link is broken. If you want to search for symbolic links when -L is in effect, use -xtype.
s socket
D door (Solaris)
-uid n File’s numeric user ID is n.
-used n
File was last accessed n days after its status was last changed.
-user uname
File is owned by user uname (numeric user ID allowed).
-writable
Matches files which are writable.
Actions
-delete
Delete files; true if removal succeeded.
-exec command ;
Execute command; true if 0 status is returned.
-exec command {} +
This variant of the -exec action runs the specified command on the selected files, but the command
line is built by appending each selected file name at the end; the total number of invocations of the
command will be much less than the number of matched files.
-fprint file
True; print the full file name into file file.
-fprintf file format
True; like -printf but write to file like -fprint.
-ok command ;
Like -exec but ask the user first.
-print True; print the full file name on the standard output, followed by a newline.
-quit Exit immediately
Example 1
search for a file using find command.
[eleiss@eleiss ~]$ find ./ -name "*hello*"
./hello-1.1.c

53 | P a g e
./hello-1.c
[eleiss@eleiss ~]$
This command finds files matching the pattern given in the current directory recursively.
Example 2
Find empty files in a directory.
[eleiss@eleiss ~]$ ls -l
total 12
-rw-rw-r--. 1 eleiss eleiss 81 Jan 1 2011 dhristadhyum
-rw-rw-r--. 1 eleiss eleiss 0 Sep 4 18:53 empty_file
-rw-rw-r--. 1 eleiss eleiss 125 Sep 4 16:02 hello-1.1.c
-rw-rw-r--. 1 eleiss eleiss 63 Sep 4 16:02 hello-1.c
[eleiss@eleiss ~]$ find ./ -empty
./empty_file
[eleiss@eleiss ~]$
The above command will search for an empty directory or regular file in the provided path recursively.
Example 3
Find all the files that were modified in last 24 hours.
total 12
[eleiss@eleiss ~]$ find ./ -mtime -1
./
./hello-1.1.c
./hello-1.c
./empty_file
[eleiss@eleiss ~]$
The command finds all the files and directories that were modified in last 24 hours.
Example 4
Find all the files which have read and write permissions for others in a directory.
total 16
-rw-r--rw-. 1 eleiss eleiss 6 Sep 4 19:01 world_writable
[eleiss@eleiss ~]$ find ./ -perm -o+rw
./world_writable
[eleiss@eleiss ~]$

54 | P a g e
The output says that "world_writable" has both read and write permissions for others.
Example 5
Remove all the files which have read and write permissions for others in a directory.
total 16
-rw-r--rw-. 1 eleiss eleiss 9 Sep 4 19:10 world_writable
[eleiss@eleiss ~]$ find ./ -type f -perm -o+rw -exec rm -fv {} ;
removed `./world_writable'
total 12
[eleiss@eleiss ~]$
First the find command will search for the files matching the given criteria and then operates
the rm command on each of them.
Users, Groups and Permissions
1. id - print real and effective user and group IDs
2. chmod - change file mode bits
3. chown - change file owner and group
4. chgrp - change group ownership
5. umask - set file creation mask
id
print real and effective user and group IDs
Syntax
id [OPTION]... [USERNAME]
Description
Print user and group information for the specified USERNAME, or (when USERNAME omitted) for the
current user.
Options
-a ignore, for compatibility with other versions

55 | P a g e
-Z, --context
print only the security context of the current user
-g, --group
print only the effective group ID
-G, --groups
print all group IDs
-n, --name
print a name instead of a number, for -ugG
-r, --real
print the real ID instead of the effective ID, with -ugG
-u, --user
print only the effective user ID
Example 1
Demonstrate id command.
[eleiss@eleiss ~]$ id
uid=501(eleiss) gid=501(eleiss) groups=501(eleiss),502(test)
context=unconfined_u:unconfined_r:unconfined_t:s0-s0:c0.c1023
[eleiss@eleiss ~]$
The user "eleiss" has user id 501 and primary group id 501. In addition the user is a member of another
group "test" whose id is 502. The remaining are SELinux properties.
chmod
change file mode bits
Syntax
chmod [OPTION]... MODE[,MODE]... FILE...
chmod [OPTION]... OCTAL-MODE FILE...
chmod [OPTION]... --reference=RFILE FILE...
Description
chmod changes the file mode bits of each given file according to mode, which can be either a symbolic
representation of changes to make, or an octal number representing the bit pattern for the new mode bits.
Options
--no-preserve-root
do not treat ‘/’ specially (the default)
-v, --verbose

56 | P a g e
output a diagnostic for every file processed
--reference=RFILE
use RFILE’s mode instead of MODE values
-R, --recursive
change files and directories recursively
Symbolic Mode
The format of a symbolic mode is [ugoa...][[+-=][perms...]...], where perms is either zero or more
letters from the set rwxXst, or a single letter from the set ugo. Multiple symbolic modes can be given,
separated by commas.
A combination of the letters ugoa controls which users’ access to the file will be changed: the user
who owns it (u), other users in the file’s group (g), other users not in the file’s group (o), or all users (a). If
none of these are given, the effect is as if a were given, but bits that are set in the umask are not affected.
The operator + causes the selected file mode bits to be added to the existing file mode bits of each
file; - causes them to be removed; and = causes them to be added and causes unmentioned bits to be
removed except that a directory’s unmentioned set user and group ID bits are not affected.
Octal Mode
A numeric mode is from one to four octal digits (0-7), derived by adding up the bits with values 4, 2, and
1. Omitted digits are assumed to be leading zeros. The first digit selects the set user ID (4) and set group
ID (2) and restricted deletion or sticky (1) attributes. The second digit selects permissions for the user
who owns the file: read (4), write (2), and execute (1); the third selects permissions for other users in the
file’s group, with the same values; and the fourth for other users not in the file’s group, with the same
values.
Example 1
Remove all permissions from a file for group and others.
total 4
-rw-rw-r--. 1 eleiss eleiss 22 Sep 4 19:22 cricket
[eleiss@eleiss ~]$ chmod g-rwx,o-rwx cricket
total 4
-rw-------. 1 eleiss eleiss 22 Sep 4 19:22 cricket
[eleiss@eleiss ~]$
Here permissions are given in symbolic representation.
Example 2
Give all the permissions for all to a file.
total 4
-rw-------. 1 eleiss eleiss 22 Sep 4 19:22 cricket

57 | P a g e
[eleiss@eleiss ~]$ chmod 777 cricket
total 4
-rwxrwxrwx. 1 eleiss eleiss 22 Sep 4 19:22 cricket
[eleiss@eleiss ~]$
Think twice before you do this. This will let everyone read, write and execute your file.
chown
change file owner and group
Syntax
chown [OPTION]... [OWNER][:[GROUP]] FILE...
chown [OPTION]... --reference=RFILE FILE...
Description
chown changes the user and/or group ownership of each given file.
If only an owner (a user name or numeric user ID) is given, that user is made the owner of each given file,
and the files’ group is not changed.
If the owner is followed by a colon and a group name (or numeric group ID), with no spaces between
them, the group ownership of the files is changed as well.
If a colon but no group name follows the user name, that user is made the owner of the files and the
group of the files is changed to that user’s login group.
If the colon and group are given, but the owner is omitted, only the group of the files is changed; in this
case, chown performs the same function as chgrp.
If only a colon is given, or if the entire operand is empty, neither the owner nor the group is changed.
Options
--dereference
affect the referent of each symbolic link (this is the default), rather than the symbolic link itself
-h, --no-dereference
affect each symbolic link instead of any referenced file (useful only on systems that can change
the ownership of a symlink)
--no-preserve-root
--preserve-root
fail to operate recursively on ‘/’
--reference=RFILE
use RFILE’s owner and group rather than specifying OWNER:GROUP values

58 | P a g e
-R, --recursive
operate on files and directories recursively
-v, --verbose
-H if a command line argument is a symbolic link to a directory, traverse it
-L traverse every symbolic link to a directory encountered
-P do not traverse any symbolic links (default)
Example 1
Change ownership of a file to root.
[root@eleiss ~]$ ls -l
total 4
[root@eleiss ~]$ chown -v root cricket
changed ownership of `cricket' to root
total 4
-rwxrwxrwx. 1 root eleiss 22 Sep 4 19:22 cricket
[root@eleiss ~]$
Only root can change the ownership.
Think what would happen if ordinary user could change the ownership of a file. :D
Example 2
Change ownership and group of a file.
total 4
-rwxrwxrwx. 1 root eleiss 22 Sep 4 19:22 cricket
[root@eleiss ~]$ chown -v eleiss:root cricket
changed ownership of `cricket' to eleiss:root
total 4
-rwxrwxrwx. 1 eleiss root 22 Sep 4 19:22 cricket
[root@eleiss ~]$
The new ownership of "cricket" is "eleiss" and group is "root".
chgrp
change group ownership
Syntax

59 | P a g e
chgrp [OPTION]... GROUP FILE...
chgrp [OPTION]... --reference=RFILE FILE...
Description
Change the group of each FILE to GROUP.
Options
--dereference
affect the referent of each symbolic link (this is the default), rather than the symbolic link itself
-h, --no-dereference
affect each symbolic link instead of any referenced file (useful only on systems that can change the
ownership of a symlink)
--no-preserve-root
--preserve-root
fail to operate recursively on ‘/’
-f, --silent, --quiet
suppress most error messages
--reference=RFILE
use RFILE’s group rather than specifying a GROUP value
-R, --recursive
operate on files and directories recursively
-v, --verbose
-H if a command line argument is a symbolic link to a directory, traverse it
-L traverse every symbolic link to a directory encountered
-P do not traverse any symbolic links (default)
Example 1
Change group of a file with chgrp command.
total 4
-rwxrwxrwx. 1 eleiss root 22 Sep 4 19:22 cricket
[eleiss@eleiss ~]$ chgrp eleiss cricket
total 4
[eleiss@eleiss ~]$
Ordinary users can change group ownership of their own files.

60 | P a g e
umask
set file creation mask
Syntax
umask [-p] [-S] [mode]
Description
The user file-creation mask is set to mode.If mode begins with a digit, it is interpreted as an octal number;
otherwise it is interpreted as a symbolic mode mask similar to that accepted by chmod(1). If mode is
omitted, the current value of the mask is printed.
Options
-S option causes the mask to be printed in symbolic form; the default output is an octal number.
-p option is supplied, and mode is omitted, the output is in a form that may be reused as input.
Example 1
Demonstration of umask command.
[eleiss@eleiss ~]$ umask
0002
[eleiss@eleiss ~]$ touch dhananjay
[eleiss@eleiss ~]$ mkdir geeta
[eleiss@eleiss ~]$ ls -l dhananjay
-rw-rw-r--. 1 eleiss eleiss 0 Sep 4 19:46 dhananjay
[eleiss@eleiss ~]$ ls -ld geeta/
drwxrwxr-x. 2 eleiss eleiss 4096 Sep 4 19:46 geeta/
[eleiss@eleiss ~]$
The newly created file "dhananjay" has permissions 0666 minus 0002 which is 0664.
The newly created directory "geeta" has permissions 0777 minus 0002 which is 0775.
Example 2
Changing umask value.
0002
[eleiss@eleiss ~]$ umask 0022
0022
[eleiss@eleiss ~]$
The new umask value does not persist and the old value comes into action once the current shell is
exited. In order to make it persistent write this command in users's system start up files.
i.e "~/.bashrc" or "~/.bash_profile".

61 | P a g e
Editors
1. vim - Vi IMproved, a programmers text editor
vim
Vi IMproved, a programmers text editor
Syntax
vim [options] [file ..]
Description
Vim is a text editor that is upwards compatible to Vi. It can be used to edit all kinds of plain text. It is
especially useful for editing programs.
There are a lot of enhancements above Vi: multi level undo, multi windows and buffers, syntax
highlighting, command line editing, filename completion, on-line help, visual selection, etc.. See ":help
vi_diff.txt" for a summary of the differences between Vim and Vi.
While running Vim a lot of help can be obtained from the on-line help system, with the ":help" command.
Options
+[num] For the first file the cursor will be positioned on line "num". If "num" is
missing, the cursor will be positioned on the last line.
+/{pat} For the first file the cursor will be positioned on the first occurrence of {pat}. See ":help
search-pattern" for the available search patterns.
+{command}
-c {command}
{command} will be executed after the first file has been read. {command} is interpreted as an Ex
command. If the {command} contains spaces it must be enclosed in double quotes (this depends on the
shell that is used). Example: Vim "+set si" main.c
-d Start in diff mode. There should be two, three or four file name arguments. Vim will open all the
files and show differences between them. Works like vimdiff(1)
-e Start Vim in Ex mode, just like the executable was called "ex".
-E Start Vim in improved Ex mode, just like the executable was called "exim".
-o[N] Open N windows stacked. When N is omitted, open one window for each file.
-O[N] Open N windows side by side. When N is omitted, open one window for each file.
-r {file} Recovery mode. The swap file is used to recover a crashed editing session. The swap file is a file
with the same filename as the text file with ".swp" appended. See ":help recovery".

62 | P a g e
Shells
1. bash - GNU Bourne-Again SHell
2. history - Access command history
3. tty - print the file name of the terminal connected to standard input
4. tee - read from standard input and write to standard output and files
5. trap - Shell built-in command to respond to kernel signals.
bash
GNU Bourne-Again SHell
Syntax
bash [options] [file]
Description
Bash is an sh-compatible command language interpreter that executes commands read from the
standard input or from a file. Bash also incorporates useful features from the Korn and C shells (ksh and
csh).
Options
-c string If the -c option is present, then commands are read from string. If there are arguments after the
string, they are assigned to the positional parameters, starting with $0.
-i If the -i option is present, the shell is interactive.
-l Make bash act as if it had been invoked as a login shell
-r If the -r option is present, the shell becomes restricted
-s If the -s option is present, or if no arguments remain after option processing, then commands are
read from the standard input. This option allows the positional parameters to be set when invoking an
interactive shell.
-D A list of all double-quoted strings preceded by $ is printed on the standard output. These are the
strings that are subject to language translation when the current locale is not C or POSIX. This implies the
-n option; no commands will be executed.
[-+]O [shopt_option]
shopt_option is one of the shell options accepted by the shopt builtin. If shopt_option is present, -O
sets the value of that option; +O unsets it. If shopt_option is not supplied, the names and values of the
shell options accepted by shopt are printed on the standard output. If the invocation option is +O, the
output is displayed in a format that may be reused as input.
-- A -- signals the end of options and disables further option processing. Any arguments after the --
are treated as filenames and arguments. An argument of - is equivalent to --.
Control Characters

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Control Characters change the behavior of the terminal or text display. A control character is a
CONTROL + key combination (pressed simultaneously). A control character may also be written in octal
or hexadecimal notation, following an escape.
 Ctrl + A - Moves cursor to beginning of line of text (on the command-line).
 Ctrl + B - Backspace (nondestructive).
 Ctrl + C - Break. Terminate a foreground job.
 Ctrl + D - Log out from a shell (similar to exit). EOF (end-of-file). This also terminates input from
stdin. When typing text on the console or in an xterm window, Ctl-D erases the character under
the cursor. When there are no characters present, Ctrl-D logs out of the session, as expected. In
an xterm window, this has the effect of closing the window.
 Ctrl + E - Moves cursor to end of line of text (on the command-line).
 Ctrl + F - Moves cursor forward one character position (on the command-line).
 Ctrl + G - BEL.
 Ctrl + H - Rubout (destructive backspace). Erases characters the cursor backs over while
backspacing.
 Ctrl + I - Horizontal tab.
 Ctrl + J - Newline (line feed).
 Ctrl + K - Vertical tab.

64 | P a g e
 Ctrl + L - Formfeed (clear the terminal screen).
 Ctrl + M - Carriage return.
 Ctrl + N - Erases a line of text recalled from history buffer(on the command-line).
 Ctrl + O - Issues a newline (on the command-line).
 Ctrl + P - Recalls last command from history buffer (on the command-line).
 Ctrl + Q - Resume
 Ctrl + R - Backwards search for text in history buffer (on the command-line).
 Ctrl + S - Suspend
 Ctrl + T - Reverses the position of the character the cursor is on with the previous character (on
the command-line).
 Ctrl + U - Erase a line of input, from the cursor backward to beginning of line.
 Ctrl + V - When inputting text, Ctrl-V permits inserting control characters.
 Ctrl + W - When typing text on the console or in an xterm window, Ctrl-W erases from the
character under the cursor backwards to the first instance of whitespace.

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 Ctrl + X - In certain word processing programs, Cuts highlighted text and copies to clipboard.
 Ctrl + Y - Pastes back text previously erased (with Ctrl-U or Ctrl-W).
 Ctrl + Z - Pauses a foreground job.
history
Access command history
Syntax
history [options]
Description
With no options, display the command history list with line numbers. Lines listed with a * have been
modified. An argument of n lists only the last n lines.
Options
-c Clear the history list by deleting all the entries.
-d offset Delete the history entry at position offset.
-a Append the ‘‘new’’ history lines (history lines entered since the beginning of the current bash
session) to the history file.
-n Read the history lines not already read from the history file into the current history list. These are
lines appended to the history file since the beginning of the current bash session.
-r Read the contents of the history file and use them as the current history.
-w Write the current history to the history file, overwriting the history file’s contents.
Example 1
Show last five commands stored in history.
[eleiss@eleiss ~]$ history | tail -5
792 ls -l
793 pwd
794 cat /etc/passwd
795 tree
796 history | tail -5

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[eleiss@eleiss ~]$
Above command shows the previous five commands run on the current shell.
Example 2
Run commands from the history.
792 ls -l
793 pwd
794 cat /etc/passwd
795 tree
[eleiss@eleiss ~]$ !793
pwd
/home/eleiss
[eleiss@eleiss ~]$
You can run commands stored in history by using their reference number. In order to run a command by
its reference number type "!" character followed by the number and press enter, the shell runs the
command stored at the number in history. Here pwd command is stored at 793 position.
Example 3
Print a command at specific position in the history.
792 ls -l
793 pwd
794 cat /etc/passwd
795 tree
[eleiss@eleiss ~]$ !793:p
pwd
[eleiss@eleiss ~]$
In order to print a command stored at some specific position in the history type "!" character followed by
the number followed by ":p"and press enter. Here in this example shell prints the command stored at
position 793 which is pwd.
tty
print the file name of the terminal connected to standard input
Syntax
tty [OPTION]...
Description
print the file name of the terminal connected to standard input

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Options
-s, --silent, --quiet
print nothing, only return an exit status
Example 1
Find the name of the current terminal.
[eleiss@eleiss ~]$ tty
/dev/pts/2
[eleiss@eleiss ~]$
Here the user "eleiss" has logged in on "/dev/pts/2" terminal.
tee
read from standard input and write to standard output and files
Syntax
tee [OPTION]... [FILE]...
Description
Read from standard input and write to standard output and files. Copy standard input to each FILE, and
also to standard output.
Options
-a, --append
append to the given FILEs, do not overwrite
-i, --ignore-interrupts
ignore interrupt signals
Example 1
Demonstrate tee command.
[eleiss@eleiss ~]$ cat names | head -5 | tee girls
divya
dharmi
priti
komal
priyanka
[eleiss@eleiss ~]$ cat girls
divya
dharmi
priti
komal
priyanka

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tulsi
vanita
rupa
[eleiss@eleiss ~]$
The above command prints first five lines from the file "names" and also stores the same output in a file
"girls" in current directory.
trap
Shell built-in command to respond to kernel signals.
Syntax
trap [-lp] [[arg] sigspec ...]
Description
The command arg is to be read and executed when the shell receives signal(s) sigspec.
Options
-l print a list of signal names and their corresponding numbers.
-p display commands to be executed by trap associated with signal
Filters
1. pr - convert text files for printing
2. head - output the first part of files
3. tail - output the last part of files
4. cut - remove sections from each line of files
5. paste - merge lines of files
6. sort - sort lines of text files
7. uniq - report or omit repeated lines
8. tr - translate or delete characters
9. sed - stream editor for filtering and transforming text
10. awk - pattern scanning and processing language
pr
convert text files for printing
Syntax
pr [OPTION]... [FILE]...
Description

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Paginate or columnate FILE(s) for printing.
Options
+FIRST_PAGE[:LAST_PAGE], --pages=FIRST_PAGE[:LAST_PAGE]
begin [stop] printing with page FIRST_[LAST_]PAGE
-COLUMN, --columns=COLUMN
output COLUMN columns and print columns down, unless -a is used. Balance number of lines in the
columns on each page.
-a, --across
print columns across rather than down, used together with -COLUMN
-c, --show-control-chars
use hat notation (^G) and octal backslash notation
-d, --double-space
double space the output
-D, --date-format=FORMAT
use FORMAT for the header date
-e[CHAR[WIDTH]], --expand-tabs[=CHAR[WIDTH]]
expand input CHARs (TABs) to tab WIDTH (8)
-F, -f, --form-feed
use form feeds instead of newlines to separate pages (by a 3-line page header with -F or a 5-line
header and trailer without -F)
-h, --header=HEADER
use a centered HEADER instead of filename in page header, -h "" prints a blank line, don’t use -h""
-J, --join-lines
merge full lines, turns off -W line truncation, no column alignment, --sep-string[=STRING] sets
separators
-l, --length=PAGE_LENGTH
set the page length to PAGE_LENGTH (66) lines (default number of lines of text 56, and with -F 63)
-m, --merge
print all files in parallel, one in each column, truncate lines, but join lines of full length with -J
Example 1
Demonstrate pr command.
[eleiss@eleiss ~]$ cat /etc/passwd | head -5 | pr -l 15 -h "Passwd File"
2011-09-12 01:57 Passwd File Page 1
root:x:0:0:root:/root:/bin/bash
bin:x:1:1:bin:/bin:/sbin/nologin

70 | P a g e
daemon:x:2:2:daemon:/sbin:/sbin/nologin
adm:x:3:4:adm:/var/adm:/sbin/nologin
lp:x:4:7:lp:/var/spool/lpd:/sbin/nologin
[eleiss@eleiss ~]$
The command in example prepares the first five lines of "/etc/passwd" for printing. The header can be
customized with -h option.
head
output the first part of files
Syntax
head [OPTION]... [FILE]...
Description
Print the first 10 lines of each FILE to standard output. With more than one FILE, precede each with a
header giving the file name. With no FILE, or when FILE is -, read standard input.
Options
-c, --bytes=[-]K
print the first K bytes of each file; with the leading ‘-’, print all but the last K bytes of each file
-n, --lines=[-]K
print the first K lines instead of the first 10; with the leading ‘-’, print all but the last K lines of each file
Example 1
Print first six lines of some output using head command.
[eleiss@eleiss ~]$ seq 1 100 | head -6
1
2
3
4
5
6
[eleiss@eleiss ~]$
You already know that the above seq command would print integer numbers from 1 to 100. But the
output is modified and the first ten lines are printed.
head command is very useful in shell scripts.

71 | P a g e
If no argument is supplied to head command, it prints first ten lines.
Example 2
Print first hundred bytes of some output using head command.
[eleiss@eleiss ~]$ cat /etc/passwd | head -c 100
root:x:0:0:root:/root:/bin/bash
bin:x:1:1:bin:/bin:/sbin/nologin
daemon:x:2:2:daemon:/sbin:/sbin/nol[eleiss@eleiss ~]$
The output is the first hundred bytes of the file "/etc/passwd"
tail
output the last part of files
Syntax
tail [OPTION]... [FILE]...
Description
Print the last 10 lines of each FILE to standard output. With more than one FILE, precede each with a
header giving the file name. With no FILE, or when FILE is -, read standard input.
Options
-c, --bytes=K
output the last K bytes; alternatively, use -c +K to output bytes starting with the Kth of each file
-f, --follow[={name|descriptor}]
output appended data as the file grows; -f, --follow, and --follow=descriptor are equivalent
-F same as --follow=name --retry
-n, --lines=K
output the last K lines, instead of the last 10; or use -n +K to output lines starting with the Kth
--max-unchanged-stats=N
with --follow=name, reopen a FILE which has not changed size after N (default 5) iterations to see if it
has been unlinked or renamed (this is the usual case of rotated log files)
--pid=PID
with -f, terminate after process ID, PID dies
-q, --quiet, --silent
never output headers giving file names
--retry

72 | P a g e
keep trying to open a file even when it is or becomes inaccessible; useful when following by name,
i.e., with --follow=name
-s, --sleep-interval=N
with -f, sleep for approximately N seconds (default 1.0) between iterations
-v, --verbose
always output headers giving file names
Example 1
Print last seven lines of some output using tail command.
[eleiss@eleiss ~]$ ls -1
autosave.xmi
bin
Desktop
Documents
Downloads
empty
Music
out.ogv
passwd
Pictures
Public
README
Templates
texput.log
VGAME
Videos
[eleiss@eleiss ~]$ ls -1 | tail -7
Pictures
Public
README
Templates
texput.log
VGAME
Videos
[eleiss@eleiss ~]$
By default if you do not supply any argument to tail command, then it prints last ten lines of the input
supplied to it.
Example 2
Print all the lines from nth line using tail command.
[eleiss@eleiss ~]$ seq 1 100 | tail -n +94
94
95
96
97
98
99
100

73 | P a g e
[eleiss@eleiss ~]$
This command prints all the lines starting from 94th line.
Example 3
Print an excerpt of some output using the combination of head and tail command.
[eleiss@eleiss ~]$ seq 1 100 | tail -n +50 | head -8
50
51
52
53
54
55
56
57
[eleiss@eleiss ~]$
The combination of head and tail commands is very much useful in shell scripts.
In this example, the seq command generates a sequence starting from 1 to 100. The output is passed
to tail command which displays the lines starting from 50 and the output is then passed
to head command which displays the first eight lines.
cut
remove sections from each line of files
Syntax
cut [OPTION]... [FILE]...
Description
Print selected parts of lines from each FILE to standard output. With no FILE, or when FILE is -, read
standard input.
Options
-b, --bytes=LIST
select only these bytes
-c, --characters=LIST
select only these characters
-d, --delimiter=DELIM
use DELIM instead of TAB for field delimiter
-f, --fields=LIST
select only these fields; also print any line that contains no delimiter character, unless the -s option is
specified

74 | P a g e
-n with -b: don’t split multibyte characters
--complement
complement the set of selected bytes, characters or fields
-s, --only-delimited
do not print lines not containing delimiters
--output-delimiter=STRING
use STRING as the output delimiter the default is to use the input delimiter
Use one, and only one of -b, -c or -f. Each LIST is made up of one range, or many ranges separated by
commas. Selected input is written in the same order that it is read, and is written exactly once. Each
range is one of:
N N’th byte, character or field, counted from 1
N- from N’th byte, character or field, to end of line
N-M from N’th to M’th (included) byte, character or field
-M from first to M’th (included) byte, character or field
Example 1
Extract username and their login shell from a /etc/passwd file.
[eleiss@eleiss ~]$ cat /etc/passwd | cut -d":" -f 1,7
root:/bin/bash
bin:/sbin/nologin
daemon:/sbin/nologin
adm:/sbin/nologin
lp:/sbin/nologin
[eleiss@eleiss ~]$
In this example ":" is provided as a delimiter to the cut command. As you may know, a password file in
Linux is a seven fields file where every field is separated by ":"
cut command is one the most used commands in shell scripts.
Example 2
Display only file types and permissions of files in the current directory.
total 24068
-rw-------. 1 eleiss eleiss 14653 Feb 3 2011 autosave.xmi
drwxr-xr-x. 2 eleiss eleiss 4096 Jun 30 17:33 Desktop
drwxr-xr-x. 2 eleiss eleiss 4096 Apr 25 00:36 Documents
drwxrwxr-x. 3 eleiss eleiss 4096 Sep 4 19:46 empty
drwxr-xr-x. 2 eleiss eleiss 4096 Aug 5 2010 Music
drwxr-xr-x. 2 eleiss eleiss 4096 Aug 7 2010 Pictures

75 | P a g e
-rw-rw-r--. 1 eleiss eleiss 618 Aug 11 2010 texput.log
drwx------. 2 eleiss eleiss 4096 May 17 23:31 VGAME
[eleiss@eleiss ~]$ ls -l | tail -n +2 | cut -b 1-10
-rw-------
drwxr-xr-x
drwxr-xr-x
drwxrwxr-x
drwxr-xr-x
-rw-rw-r--
drwxr-xr-x
-rw-rw-r--
drwx------
[eleiss@eleiss ~]$
tail command eliminates the first line from the output of ls -l command. As you know that the first ten
characters of the output are the file type and permissions. The cut command extracts first ten characters
from each line.
paste
merge lines of files
Syntax
paste [OPTION]... [FILE]...
Description
Write lines consisting of the sequentially corresponding lines from each FILE, separated by TABs, to
standard output. With no FILE, or when FILE is -, read standard input.
Options
-d, --delimiters=LIST
reuse characters from LIST instead of TABs
-s, --serial
paste one file at a time instead of in parallel
Example 1
Paste two files using paste command.
[eleiss@eleiss ~]$ cat name
Pintu
Manoj
Paresh
Rajni
Nitin
[eleiss@eleiss ~]$ cat roll
11
12
15

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17
20
[eleiss@eleiss ~]$ paste name roll
Pintu 11
Manoj 12
Paresh 15
Rajni 17
Nitin 20
Here the paste command pastes two separate files "name" and "roll"
sort
sort lines of text files
Syntax
sort [OPTION]... [FILE]...
Description
Write sorted concatenation of all FILE(s) to standard output.
Options
-b, --ignore-leading-blanks
ignore leading blanks
-d, --dictionary-order
consider only blanks and alphanumeric characters
-f, --ignore-case
fold lower case to upper case characters
-g, --general-numeric-sort
compare according to general numerical value
-i, --ignore-nonprinting
consider only printable characters
-M, --month-sort
compare (unknown) < ‘JAN’ < ... < ‘DEC’
-h, --human-numeric-sort
compare human readable numbers (e.g., 2K 1G)
-n, --numeric-sort
compare according to string numerical value
-R, --random-sort
sort by random hash of keys
--random-source=FILE

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