Command line essentials

Introduction
Working on the command line
Manuals
Essential command line tools

Command line essentials

Bart Van Loon

1st February 2012

1 / 30 Bart Van Loon Command line essentials

Introduction
Manuals

1 Introduction

2 Working on the command line
bash
bash prompt
some bash features

3 Manuals

4 Essential command line tools


Introduction
Manuals

Some ancient history
When computers were big, incomprehensible beasts, like

you could “talk” to it using punched cards, paper tape or a
terminal.

Introduction
Manuals

This is such a computer terminal:

The famous DEC VT100 (1978).

Introduction
Manuals

These terminals gave you an interface for text entry and display
through various standard “streams”.


Introduction
Manuals

A little less ancient now
Today, most UNIX-like operating systems such as Linux and
FreeBSD have virtual terminals to provide several text terminals on
a single computer to let you interface with the computer itself.

If you’re in X now, try to press ctrl-alt-F1, ctrl-alt-F2, . . .

Introduction
Manuals

Modern times

In today’s graphical world, we have terminal emulators, like

xterm
gnome-terminal
rxvt
...


Introduction
Manuals

Modern times
These terminal emulators run text-based applications. The most
fundamental types of such applications are shells, like

bash
tcsh
zsh
...

A shell gives you a command line interface (CLI).

Introduction
bash
bash prompt
Manuals
some bash features


Let’s assume you are running bash.
bash is program, namely a shell meant for interactive use
bash is also a powerful scripting language


Introduction
bash
bash prompt
Manuals
some bash features

bash in interactive mode

When it starts, it runs one or more scripts:
When started as an interactive login shell:
/etc/profile
~/.bash profile, ~/.bash login, or ~/.profile
When exited as a login shell:
~/.bash logout
When started as an interactive shell (but not a login shell):
~/.bashrc


Introduction
bash
bash prompt
Manuals
some bash features

Your bash prompt

Let’s start with what you see:

bbbart@tuxitree:~$

bbbart : my username
tuxitree : computer’s hostname
˜ : present working directory (˜ is the home directory)
$ : this means I am not root


Introduction
bash
bash prompt
Manuals
some bash features

Your bash prompt

You can change the look of this prompt! Why would you do so?
it looks cool;
it’s useful to keep track of system information;
diﬀerent machines/users can get diﬀerent colours;
have information about work environment available at all time;
to quickly spot the prompt when you use scrollback;
...


Introduction
bash
bash prompt
Manuals
some bash features

Your bash prompt

Your prompt conﬁguration is stored in the variable PS1.
$ echo $PS1
u@h:w$

u : user’s username
h : computer’s hostname
w : present working directory
$ : $ when user is not root, # when user is root


Introduction
bash
bash prompt
Manuals
some bash features

Your bash prompt

Try the following command (put it on one line with spaces in
between):

PS1=’[e[1;32m]u@H:[e[m]
[e[1;37m]w[e[m]n[e[1;33m]hist:!
[e[0;33m] [e[1;31m]jobs:j $[e[m] ’

Now go an ﬁnd the prompt that suits you best!


Introduction
bash
bash prompt
Manuals
some bash features

Keyboard shortcuts

Some useful keyboard shortcuts:
tab : autocomplete from the cursor position
ctrl-a : move cursor to the line start
ctrl-c : send the SIGINT signal to the current task
ctrl-d : send an EOF marker (if the line is empty)
ctrl-e : move cursor to the line end
ctrl-k : clear the line after the cursor
ctrl-l : clear the screen content
ctrl-u : clear the line before the cursor
ctrl-z : send the SIGTSTP signal to the current task


Introduction
bash
bash prompt
Manuals
some bash features

Stream redirecting

Remember the streams to interact with a terminal (stdin,
stdout, stderr). You can redirect them!

> : redirect stdout
2> : redirect stderr
< : redirect stdin

Special one:
>> : redirect stdout, but append to the output


Introduction
bash
bash prompt
Manuals
some bash features

Piping

You can also “pipe” streams to link commands:

$ program1 | program2

is the same as
$ program1 > tempfile
$ program2 < tempfile
$ rm tempfile


Introduction
bash
bash prompt
Manuals
some bash features

Piping


Introduction
bash
bash prompt
Manuals
some bash features

Learn from history

DRY is also a principle on the shell:
↑ and ↓ : navigate through your history
ctrl-r : search the command history
history : print your recent history
!<n> : repeat command number <n>
!! : repeat the last command
!$ : special variable that contains the last word of the
previous command


Introduction
Manuals

Before we begin. . .

The most important command you’ll ever learn, is man:
man : format and display the manual pages

Most manual pages contain a synopsis of the command in
question:
mysql [options] db name
mysql can take some options but has to have a name of a
database as argument
xpdf [options] [PDF-file [page | +dest]]
xpdf can take some options and a PDF-ﬁle as arguments. If
you pass a PDF-ﬁle as argument you can also give it a page or
a destination, preceded by a +-symbol.

Now check the synopsis of the ssh command.

Introduction
Manuals


“The right tool for the right job”
cut : remove sections from each line of files
du : estimate file space usage
grep : print lines matching a pattern
head : output the first part of files
nice : run a program with modified scheduling priority
sort : sort lines of text files
tail : output the last part of files
wc : print newline, word, and byte counts


Introduction
Manuals

cut

Name : cut
Description : remove sections from each line of files
Synopsis : cut OPTION... [FILE]...

Useful options:
-d DELIM : use DELIM instead of TAB for field delimiter
-f LIST : select only these fields

A LIST is made up or ranges separated by commas. A range is N,
N-, N-M or -M.


Introduction
Manuals

du

Name : du
Description : estimate ﬁle space usage
Synopsis : du [OPTION]... [FILE]...

Useful options:
-c : produce a grand total
-s : display only a total for each argument
-h : print sizes in human readable format


Introduction
Manuals

grep

Name : grep
Description : print lines matching a pattern
Synopsis : grep [OPTIONS] PATTERN [FILE...]

Useful options:
-i : ignore case distinctions in the PATTERN
-v : invert the sense of matching, to select
non-matching lines
-n : preﬁx each line of output with the 1-based line
number within its input ﬁle


Introduction
Manuals

head

Name : head
Description : output the first part of files
Synopsis : head [OPTION]... [FILE]...

Useful options:
-n K : print the first K lines instead of the first 10


Introduction
Manuals

nice

Name : nice
Description : run a program with modiﬁed scheduling priority
Synopsis : nice [OPTION] [COMMAND [ARG]...]

Useful options:
-n N : add integer N to the niceness (default 10)


Introduction
Manuals

sort

Name : sort
Description : sort lines of text ﬁles
Synopsis : sort [OPTION]... [FILE]...

Useful options:
-h : compare human readable numbers
-n : compare according to string numerical value
-r : reverse the result of comparisons
-u : output only the ﬁrst of an equal run


Introduction
Manuals

tail

Name : tail
Description : output the last part of ﬁles
Synopsis : tail [OPTION]... [FILE]...

Useful options:
-f : output appended data as the ﬁle grows
-n K : print the last K lines instead of the last 10


Introduction
Manuals

wc

Name : wc
Description : print newline, word, and byte counts for each ﬁle
Synopsis : wc [OPTION]... [FILE]...

Useful options:
-l : print the newline counts


Introduction
Manuals

References

http://en.wikipedia.org/wiki/Computer_terminal
http://en.wikipedia.org/wiki/Bash_%28Unix_shell%29
http://tldp.org/HOWTO/Bash-Prompt-HOWTO
http://en.wikipedia.org/wiki/Redirection_%28computing%29


Command line essentials

Recommended

Recommended

More Related Content

Similar to Command line essentials

Similar to Command line essentials (14)

More from Bart Van Loon

More from Bart Van Loon (6)

Recently uploaded

Recently uploaded (20)

Command line essentials