This document discusses basic shell scripting in Unix. It covers different shell types in Unix like Bourne shell, bash, c-shell, korn shell, and tc shell. It describes how to execute shell scripts and discusses command line editing. The document also covers basic vi commands, entering and changing text, deletion commands, and moving around in the history file. Additionally, it discusses shell variables like positional parameters, special parameters, and named variables. Other topics covered include accepting user input, displaying data, comments, test commands, logical operators, and the expr command.

1. UNIX
Basic Shell Scripting
Presentation By
Nihar R Paital

2. Shell Types in Unix
 Bourne Shell.
 Bourne Again Shell (bash).
 C Shell (c-shell).
 Korn Shell (k-shell).
 TC Shell (tcsh)
Nihar R Paital

3. Executing a shell script
 There are many ways of executing a shell script:
– By passing the shell script name as an argument to the shell. For
example:
– sh script1.sh
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4. Shell Scripts
 A script, or file that contains shell commands, is a shell program
 There are two ways to run a script
 1 By using . (dot) command
 Ex:-
 Scriptname
– By typing scriptname , if the current directory is part of command
search path . If dot isn’t in your path then type
– . /scriptname
Nihar R Paital

5. Command-line Editing
Enabling Command-line Editing
There are two ways of entering either editing mode
Add following line in .profile file
 $ set -o emacs
or
 $ set -o vi
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6. Simple Control Mode Commands
Basic vi Control Mode Commands
Command Description
 h Move left one character
 l Move right one character
 w Move right one word
 b Move left one word
 e Move to end of current word
 0 Move to beginning of line
 ^ Move to first non-blank character in line
 $ Move to end of line
Nihar R Paital

7. Entering and Changing Text
Commands for Entering vi Input Mode
Command Description
 i Text inserted before current character (insert)
 a Text inserted after current character (append)
 I Text inserted at beginning of line
 A Text inserted at end of line
 R Text overwrites existing text
Nihar R Paital

8. Deletion Commands
 Command Description
 dh Delete one character backwards
 dl Delete one character forwards
 db Delete one word backwards
 dw Delete one word forwards
 d$ Delete to end of line
 d0 Delete to beginning of line
 u undoes the last text modification
command only
 . redoes the last text modification
command.
Nihar R Paital

9. Moving Around in the History File
 Command Description
 k or - Move backward one line
 j or + Move forward one line
 G Move to line given by repeat count
 ?string Search backward for string
 /string Search forward for string
 n Repeat search in same direction as
previous
 N Repeat search in opposite direction of
previous
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10. The fc Command
 fc (fix command) is a shell built-in command
 It is used to edit one or more commands with editor, and to
run old commands with changes without having to type the
entire command in again
 The fc -l is to lists previous commands.
 It takes arguments that refer to commands in the history file.
Arguments can be numbers or alphanumeric strings
 To see only commands 2 through 4, type fc -l 2 4
 To see only one command type fc -l 5
 To see commands between ls and cal in history ,type fc -l l c
 To edit , fc command_no
Nihar R Paital

11. The fc Command
 With no arguments, fc loads the editor with the most recent command.
 With a numeric argument, fc loads the editor with the command with
that number.
 With a string argument, fc loads the most recent command starting
with that string.
 With two arguments to fc, the arguments specify the beginning and
end of a range of commands,
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12. Shell Variables.
 Positional Parameters.
 Special Parameters.
 Named variables
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13. Positional Parameters. of arguments in command line.
Acquire values from the position

– $1, $2, $3,..$9
– sh file1 10 20 30
– Ex: Suppose the content of the below file test1.sh is
#!/bin/ksh
echo Your arguments are $1 $2 $3
-Run the file test1.sh as
$ test1.sh 10 15 20
Output:
Your arguments are 10 15 20
Nihar R Paital

14. Special Parameters.
 Shell assigns the value for this parameter.
– $$ - PID number.
– $# - Number of Command Line Arguments.
– $0 – Command Name.
– $* - Displays all the command line arguments.
– $? – Exit Status.
– $- - Shell options
– $! - Process number of the last background command
– $@ - Same as $*, except when enclosed in double quotes.
Nihar R Paital

15. Exit Status
 Every UNIX command , at the end of its execution returns a status number to
the process that invoked it.
 Indicates whether or not the command ran successfully.
 An exit status of zero is used to indicate successful completion. A nonzero exit
status indicates that the program
failed.
 The shell sets the $? variable to the exit status of the last
foreground command that was executed.
 The constructs if, while, until and the logical AND (&&)
and OR (||) operators use exit status to make logical
decisions:
0 is a logical "true" (success)
1 is a logical "false" (failure)
 There are built-in true and false commands which you can
use.
Nihar R Paital

16. Exit Status
 A shell, like any other process, sets an exit status when it
finishes
executing. Shell scripts will finish in one of the following ways:
 Abort - If the script aborts due to an internal errorand exit or return
command, the exit
status is that set by those commands.
, the exit status is
that of the last command (the one that aborted the script).
 End - If the script runs to completion, the exit status is that of the last
command in the script
 Exit - If the script encounters
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17. Named Variables.
 User-defined variable that can be assigned a value.
 Used extensively in shell-scripts.
 Used for reading data, storing and displaying it.
Nihar R Paital

18. Accepting Data from User.
 read.
– Accepts input from the user.
– Syntax : read variable_name.
– Example :
$ read sname # This will prompt for user input
Here sname is the user defied variable
Nihar R Paital

19. Display Data.
 echo
– Used to display a message or any data as required by the user.
– echo [Message, Variable]
– Example:
$ echo “IBM.”
$ echo $sname # This will display the value of sname
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20. Comment Line
 Normally we use the comment lines for documentation purpose.
 The comment lines are not compiled by the compiler
 For make a line a comment line we use # symbol at the beginning of
the line
 For Ex:
# This is the First Program
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21. test command.
 Used extensively for evaluating shell script conditions.
 It evaluates the condition on its right and returns a true or false exit
status.
 The return value is used by the construct for further execution.
 In place of writing test explicitly, the user could also use [ ].
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22. test command (Contd).
 Operators used with test for evaluating numeral data are:
-eq  Equal To
-lt  Less than
-gt  Greater than
-ge  Greater than or equal to
-le  Less than or equal to
-ne  not equal to
 Operators used with test for evaluating string data are:
str1 = str2  True if both equals
str1 != str2  True if not equals
-n str1 True if str1 is not a null string
-z str1  True if str1 is a null string Nihar R Paital

23. test command (Contd).
 Operators used with test for evaluating file data are:
-f file1  True if file1 exists and is a regular file.
-d file1  True if file1 exists and is directory.
-s file1 True if file1 exists and has size greater than 0
-r file1  True if file1 exists and is readable.
-w file1  True if file1 exists and is writable.
-x file1  True if file1 exists and is executable.
Nihar R Paital

24. Logical Operators.
 Logical Operators used with test are:
 !  Negates the expression.
 -a  Binary ‘and’ operator.
 -o  Binary ‘or’ operator.
Nihar R Paital

25. expr command.
 Used for evaluating shell expressions.
 Used for arithmetic and string operations.
– Example : expr 7 + 3 Operator has to be preceded and followed by a space.
would give an output 10.
 When used with variables, back quotes need to be used.
Nihar R Paital

26. expr command.
String operations
Expr can perform three important string functions:
 1) Determine the length of the string
 2) Extract a substring
 3) Locate the position of a character in a string
For manipulating strings ,expr uses two expressions seperated by a
colon.The string to be worked upon is placed on the left of the : and a
regular expression is placed on its right.
Nihar R Paital

27. 1) The length of the string
$ x="shellscripting"
$ expr length $x
$ expr $x : '.*'
$ expr "unix training" : '.*'
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28. 2) Extracting a substring
Syntax: expr substr string position length
Substr is a keyword , string is any string
$ x="IBMIndia"
$ expr substr $x 2 3
$ y=unix
$ expr "$y" : '..(..)'
O/p :- ix
$ expr "$y" : '.(..)'
O/p: - ni
$ expr " abcdef" : '..(...)'
O/p:- bcd
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29. 3) Locating position of a character
$ expr index $x chars
 Index is a keyword
 X is a variable
 Chars is any character of a string whose position is to be located
 x=shell
$ expr index $x e
O/p:- 3
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30. Conditional Execution.
 &&
– The second command is executed only when first is successful.
– command1 && command2
 ||
– The second command is executed only when the first is
unsuccessful.
– command1 || command2
Nihar R Paital

31. Program Constructs
 if
 for
 while
 until
 case
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32. if statement.
 Syntax
if control command
then
<commands>
else
<commands>
fi
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33. Ex:if statement.
 1) If [ 10 -gt 5 ]
then
echo hi
else
echo bye
fi
 2) If grep "unix" xyz && echo found
then
ls -l xyz
fi
Nihar R Paital

34. Nihar R Paital