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

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