Command line essentials

IntroductionWorking on the command line

ManualsEssential command line tools

Command line essentials

Bart Van Loon

1st February 2012

1 / 30 Bart Van Loon Command line essentials



1 Introduction

2 Working on the command linebash

bash promptsome bash features

3 Manuals

4 Essential command line tools




Some ancient history

When computers were big, incomprehensible beasts, like

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





This is such a computer terminal:

The famous DEC VT100 (1978).4 / 30 Bart Van Loon Command line essentials




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




A little less ancient now

Today, most UNIX-like operating systems such as Linux andFreeBSD have virtual terminals to provide several text terminals ona 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, . . .




Modern times

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

I xterm

I gnome-terminal

I rxvt

I . . .




Modern times

These terminal emulators run text-based applications. The mostfundamental types of such applications are shells, like

I bash

I tcsh

I zsh

I . . .

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




bashbash promptsome bash features

Working on the command line

Let’s assume you are running bash.

I bash is program, namely a shell meant for interactive use

I bash is also a powerful scripting language





bash in interactive mode

When it starts, it runs one or more scripts:I When started as an interactive login shell:

/etc/profile

~/.bash profile, ~/.bash login, or ~/.profile

I When exited as a login shell:

~/.bash logout

I When started as an interactive shell (but not a login shell):

~/.bashrc





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





Your bash prompt

You can change the look of this prompt! Why would you do so?

I it looks cool;

I it’s useful to keep track of system information;

I different machines/users can get different colours;

I have information about work environment available at all time;

I to quickly spot the prompt when you use scrollback;

I . . .





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





Your bash prompt

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

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!





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





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





Piping

You can also “pipe” streams to link commands:

$ program1 | program2

is the same as

$ program1 > tempfile

$ program2 < tempfile

$ rm tempfile





Piping





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 theprevious command




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 inquestion:

I mysql [options] db name

mysql can take some options but has to have a name of adatabase as argument

I xpdf [options] [PDF-file [page | +dest]]

xpdf can take some options and a PDF-file as arguments. Ifyou pass a PDF-file as argument you can also give it a page ora destination, preceded by a +-symbol.

Now check the synopsis of the ssh command.




Essential command line tools

“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




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.




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




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 selectnon-matching lines

-n : prefix each line of output with the 1-based linenumber within its input file




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




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)




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




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




wc

Name : wc

Description : print newline, word, and byte counts for each file

Synopsis : wc [OPTION]... [FILE]...

Useful options:

-l : print the newline counts




References

I http://en.wikipedia.org/wiki/Computer_terminal

I http://en.wikipedia.org/wiki/Bash_%28Unix_shell%29

I http://tldp.org/HOWTO/Bash-Prompt-HOWTO

I http://en.wikipedia.org/wiki/Redirection_%28computing%29


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

Technology

Command line essentials