Customize the bash shell environments

Jump to navigation Jump to search

← Bash variable existence check • Home • Recalling command history →

Strictly speaking there are two types of shell variables:
1. Local variables (shell variable) - Used by shell and or user scripts. All user created variables are local unless exported using the export command.
2. Environment variables - Used by shell or user but they are also passed onto other command. Environment variables are passed to subprocesses or subshells.

How do I configure and customize the Bash shell environment?

Your Bash shell can be configured using the following:

What should I put in shell starup files for customization?

A typically Linux or UNIX user do the following:

Setup a custom prompt.
Setup terminal settings depending on which terminal you're using.
Set the search path such as JAVA_HOME, and ORACLE_HOME.
Set environment variables as needed by programs.
Run commands that you want to run whenever you log in or log out.

How do I view local variables?

Use the set built-in command to view all variables:

set

Usually, all upper-case variables are set by bash. For example,

echo $SHELL echo $MAIL

How do I export local variables?

Use the export command:

export EDITOR=/usr/bin/vim

export DISPLAY environment variable and run xeyes

export DISPLAY=localhost:11.0 xeyes

Be careful when changing the shell variables. For a complete list of variables set by shell, read the man page for bash by typing the following command:

man bash

How do I view environment variables?

Use the env command to view all environment variables:

env

Sample outputs:

ORBIT_SOCKETDIR=/tmp/orbit-vivek SSH_AGENT_PID=4296 GPG_AGENT_INFO=/tmp/gpg-ElCDl5/S.gpg-agent:4297:1 TERM=xterm SHELL=/bin/bash XDG_SESSION_COOKIE=186611583e30fed08439ca0047067c9d-1255929792.297209-1700262470 GTK_RC_FILES=/etc/gtk/gtkrc:/home/vivek/.gtkrc-1.2-gnome2 WINDOWID=48252673 GTK_MODULES=canberra-gtk-module USER=vivek SSH_AUTH_SOCK=/tmp/keyring-s4fcR1/socket.ssh GNOME_KEYRING_SOCKET=/tmp/keyring-s4fcR1/socket SESSION_MANAGER=local/vivek-desktop:/tmp/.ICE-unix/4109 USERNAME=vivek DESKTOP_SESSION=gnome PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games GDM_XSERVER_LOCATION=local PWD=/home/vivek LANG=en_IN GDM_LANG=en_IN GDMSESSION=gnome SHLVL=1 HOME=/home/vivek GNOME_DESKTOP_SESSION_ID=this-is-deprecated LOGNAME=vivek DBUS_SESSION_BUS_ADDRESS=unix:abstract=/tmp/dbus-16XVNAMkFB,guid=0acb6a08e3992ccc7338726c4adbf7c3 XDG_DATA_DIRS=/usr/local/share/:/usr/share/:/usr/share/gdm/ WINDOWPATH=7 DISPLAY=:0.0 COLORTERM=gnome-terminal XAUTHORITY=/home/vivek/.Xauthority OLDPWD=/usr/share/man _=/usr/bin/env

Common Environment Variables

HOME - Your home directory path.
PATH - Set your executable search path.
PWD - Your current working directory.
See more standard environment variables list.

How do I locate command?

The which command displays the pathnames of the files which would be executed in the current environment. It does this by searching the PATH for executable files matching the names of the arguments.

which command-name

Show fortune command path which print a random, hopefully interesting, adage on screen. Type the following command:

which fortune

Sample output:

/usr/games/fortune

Display your current PATH:

echo $PATH

Sample outputs:

/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games

Customize your PATH variable and remove /usr/games from PATH:

export PATH=/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin

Now, try searching fortune command path, enter:

which fortune

Try executing fortune command:

fortune

Sample outputs:

-bash: fortune: command not found

The fortune command could not be located because '/usr/games' is not included in the PATH environment variable. You can type full command path (/usr/games/fortune) or simply add /usr/games to PATH variable:

export PATH=$PATH:/usr/games fortune

Sample outputs:

Your lucky number has been disconnected.

whereis command

The whereis command is used to locate the binary, source, and manual page files for a command.

whereis command-name whereis ls

Sample outputs:

ls: /bin/ls /usr/share/man/man1/ls.1.gz

whatis command

The whatis command is used display a short description about command. whatis command searches the manual page names and displays the manual page descriptions for a command:

whatis command-name whatis date whatis ip whatis ifconfig whatis ping

Sample outputs:

date (1) - print or set the system date and time ifconfig (8) - configure a network interface ping (8) - send ICMP ECHO_REQUEST to network hosts

Recalling command history

Jump to navigation Jump to search

← Customize the bash shell environments • Home • Path name expansion →

Bash keeps a command history in buffer or a default file called ~/.bash_history.
The history buffer can hold many commands.
Use history command to display a list of command you entered at a shell prompt. You can also repeat commands stored in history.
The history command displays the history list with line numbers.
By default history is enabled but can be disabled using set builtin command.
You can recall the basic command with arrow keys.

See list of executed commands

Type the following command

history

Sample outputs:

3  tail -f /var/log/maillog
4  cat /etc/resolv.conf 
5  vnstat
6  vnstat -m
7  rpm -qa | grep vnstat
8  yum update vnstat
9  cd /opt/

10 wget http://humdi.net/vnstat/vnstat-1.9.tar.gz 11 tar -zxvf vnstat-1.9.tar.gz 12 cd vnstat-1.9 13 ls 14 vi INSTALL 15 make 16 cd examples/ 17 ls 18 vi vnstat.cgi 19 cd .. 20 ls 21 cd cfg/ 22 ls 23 vi vnstat.conf 24 cd /t, 25 cd /tmp/ 26 yumdownloader --source vnstat 27 rpm -ivh vnstat-1.6-1.el5.src.rpm 28 cd -

Recall commands

Simply hit [Up] and [Down] arrow keys.

Interactively search history

Press [CTRL-r] from the shell prompt to search backwords through history buffer or file for a command:

(reverse-i-search)`rpm ': rpm -ql rhn-client-tools-0.4.20-9.el5

To repeat last command

Just type !! at a shell prompt:

date !!

To repeat last command started with ...

Recall the most recent command starting with vn

date vnstat ls ifconfig route -n !vn

To repeat a command by its number

Recall to command line number 13:

history !13

See history command help page for more detailed information about the events and usage:

man bash help history

This is what it prints:

history: history [-c] [-d offset] [n] or history -anrw [filename] or history -ps arg [arg...] Display or manipulate the history list.

Display the history list with line numbers, prefixing each modified
entry with a `*'.  An argument of N lists only the last N entries.

Options:
  -c	clear the history list by deleting all of the entries
  -d offset	delete the history entry at position OFFSET. Negative
		offsets count back from the end of the history list

  -a	append history lines from this session to the history file
  -n	read all history lines not already read from the history file
		and append them to the history list
  -r	read the history file and append the contents to the history
		list
  -w	write the current history to the history file

  -p	perform history expansion on each ARG and display the result
		without storing it in the history list
  -s	append the ARGs to the history list as a single entry

If FILENAME is given, it is used as the history file.  Otherwise,
if HISTFILE has a value, that is used, else ~/.bash_history.

If the HISTTIMEFORMAT variable is set and not null, its value is used
as a format string for strftime(3) to print the time stamp associated
with each displayed history entry.  No time stamps are printed otherwise.

Exit Status:
Returns success unless an invalid option is given or an error occurs.

Path name expansion

Jump to navigation Jump to search

← Recalling command history • Home • Create and use aliases →

Bash shell support path name expansion using the following techniques. Let us see examples and syntax.

Curly braces

A curly braces ({..}) expands to create pattern and syntax is:

{ pattern1, pattern2, patternN } text{ pattern1, pattern2, patternN } text1{ pattern1, pattern2, patternN }text2 command something/{ pattern1, pattern2, patternN }

It will save command typing time.
Arbitrary strings may be generated.

Examples

Create a string pattern:

echo I like {tom,jerry}

Sample outputs:

I like tom jerry

A string is created, however this can be used to create unique file names:

echo file{1,2,3}.txt

Sample outputs:

file1.txt file2.txt file3.txt

echo file{1..5}.txt

Sample outputs:

file1.txt file2.txt file3.txt file4.txt file5.txt

The filenames generated do not need to exist. You can also run a command for every pattern inside the braces. Usually, you can type the following to list three files:

ls -l /etc/resolv.conf /etc/hosts /etc/passwd

But, with curly braces:

ls /etc/{resolv.conf,hosts,passwd}

Sample outputs: To remove files called hello.sh, hello.py, hello.pl, and hello.c, enter:

rm -v hello.{sh,py,pl,c}

Another example:

D=/webroot mkdir -p $D/{dev,etc,bin,sbin,var,tmp}

Wildcards

Bash supports the following three simple wildcards:
1. ***** - Matches any string, including the null string
2. ? - Matches any single (one) character.
3. [...] - Matches any one of the enclosed characters.

Examples

To display all configuration (.conf) files stored in /etc directory, enter:

ls /etc/*.conf

To display all C project header files, enter:

ls *.h

To display all C project .c files, enter:

ls *.c

You can combine wildcards with curly braces:

ls *.{c,h}

Sample outputs:

f.c fo1.c fo1.h fo2.c fo2.h fo3.c fo3.h fo4.c fo4.h fo5.c fo5.h t.c

To list all png file (image1.png, image2.png...image7.png, imageX.png), enter:

ls image?.png

To list all file configuration file start with either letter a or b, enter:

ls /etc/[ab]*.conf

← Recalling command history • Home • Create and use aliases →

Categories:

Search

Tools

Create and use aliases

Jump to navigation Jump to search

← Path name expansion • Home • The tilde expansion →

An alias is nothing but shortcut to commands.
Use alias command to display list of all defined aliases.
Add user defined aliases to ~/.bashrc file.

Create and use aliases

Use the following syntax:

alias name='command' alias name='command arg1 arg2'

Examples

Create an aliase called c to clear the terminal screen, enter:

alias c='clear'

To clear the terminal, enter:

Create an aliase called d to display the system date and time, enter:

alias d='date' d

Sample outputs:

Tue Oct 20 01:38:59 IST 2009

How do I remove the alias?

Aliases are created and listed with the alias command, and removed with the unalias command. The syntax is:

unalias alias-name unalias c unalias c d

To list currently defined aliases, enter:

alias

alias c='clear' alias d='date'

If you need to unalise a command called d, enter:

unalias d alias

If the -a option is given, then remove all alias definitions, enter:

unalias -a alias

How do I permanently add aliases to my session?

If you want to add aliases for every user, place them either in /etc/bashrc or /etc/profile.d/useralias.sh file. Please note that you need to create /etc/profile.d/useralias.sh file.
User specific alias must be placed in ~/.bashrc ($HOME/.bashrc) file.

Sample ~/.bashrc file

Example ~/.bashrc script:

make sure bc start with standard math library

alias bc='bc -l'

protect cp, mv, rm command with confirmation

alias cp='cp -i' alias mv='mv -i' alias rm='rm -i'

Make sure dnstop only shows eth1 stats

alias dnstop='dnstop -l 5 eth1'

Make grep pretty

alias grep='grep --color'

ls command shortcuts

alias l.='ls -d .* --color=tty' alias ll='ls -l --color=tty' alias ls='ls --color=tty'

Centos/RHEL server update

alias update='yum update' alias updatey='yum -y update'

vi is vim

alias vi='vim'

Make sure vnstat use eth1 by default

alias vnstat='vnstat -i eth1'

How do I ignore an alias?

Consider the following example:

alias ls='ls --color'

To ignore an alias called ls and run ls command, enter[1]:

\ls

"ls"

Or just use the full path:

/bin/ls $(which ls)

References

↑ Bash Shell: Ignore Aliases / Functions When Running A Command

Changing bash prompt

Jump to navigation Jump to search

← Using aliases • Home • Setting shell options →

Task: You need to customize your bash prompt by editing PS1 variable.
Display, your current prompt setting, enter:

echo $PS1

Sample outputs:

\u@\h:\w$

For testing purpose set PS1 as follows and notice the change:

PS1='your wish is my command : '

Sample outputs:

vivek@vivek-desktop:~$ PS1='your wish is my command : ' your wish is my command :

Customizing Prompt

Bash shell allows prompt strings to be customized by inserting a number of backslash-escaped special characters. Quoting from the bash man page:

Sequence

Description

An ASCII bell character (07)

The date in "Weekday Month Date" format (e.g., "Tue May 26")

An ASCII escape character (033)

The hostname up to the first .

The hostname (FQDN)

The number of jobs currently managed by the shell

The basename of the shell’s terminal device name

Newline

Carriage return

The name of the shell, the basename of $0 (the portion following the final slash)

The current time in 24-hour HH:MM:SS format

The current time in 12-hour HH:MM:SS format

The current time in 12-hour am/pm format

The current time in 24-hour HH:MM format

The username of the current user

The version of bash (e.g., 2.00)

\V T

The release of bash, version + patch level (e.g., 2.00.0)

The current working directory, with $HOME abbreviated with a tilde

The basename of the current working directory, with $HOME abbreviated with a tilde

The history number of this command

The command number of this command

If the effective UID is 0, a #, otherwise a $

\nnn

The character corresponding to the octal number nnn

A backslash

[

Begin a sequence of non-printing characters, which could be used to embed a terminal control sequence into the prompt

]

End a sequence of non-printing characters

You can use above backslash-escaped sequence to display name of the host with current working directory:

PS1='\h \W $ '

Adding color to prompt

It is quite easy to add colors to your prompt. Set green color prompt for normal user account[1]:

export PS1='[\e[1;32m][\u@\h \W]$[\e[0m] '

And red color prompt for root user account:

export PS1='[\e[1;31m][\u@\h \W]$[\e[0m] '

How do I make prompt setting permanent?

Edit your ~/.bashrc or ~/.bash_profile

vi ~/.bashrc

Append your PS1 definition:

export PS1='[\e[1;32m][\u@\h \W]$[\e[0m] '

Save and close the file.

PROMPT_COMMAND variable

If PROMPT_COMMAND environment variable set, the value is executed as a command prior to issuing each primary prompt. In other words, the contents of this variable are executed as a regular Bash command just before Bash displays a prompt[2]:

PROMPT_COMMAND="echo Yahooo"

Sample outputs:

[vivek@vivek-desktop man]$ PROMPT_COMMAND="echo Yahooo" Yahooo [vivek@vivek-desktop man]$ date Tue Oct 20 23:50:01 IST 2009 Yahooo

Creating complex prompt

Edit ~/.bashrc file:

vi ~/.bashrc

Add the following two shell functions [3]

bash_prompt_command() { # How many characters of the $PWD should be kept local pwdmaxlen=25 # Indicate that there has been dir truncation local trunc_symbol=".." local dir=${PWD##/} pwdmaxlen=$(( ( pwdmaxlen < ${#dir} ) ? ${#dir} : pwdmaxlen )) NEW_PWD=${PWD/#$HOME/~} local pwdoffset=$(( ${#NEW_PWD} - pwdmaxlen )) if [ ${pwdoffset} -gt "0" ] then NEW_PWD=${NEW_PWD:$pwdoffset:$pwdmaxlen} NEW_PWD=${trunc_symbol}/${NEW_PWD#/} fi }

bash_prompt() { case $TERM in xterm*|rxvt*) local TITLEBAR='[\033]0;\u:${NEW_PWD}\007]' ;; *) local TITLEBAR="" ;; esac local NONE="[\033[0m]" # unsets color to term's fg color

# regular colors
local K="\[\033[0;30m\]"    # black
local R="\[\033[0;31m\]"    # red
local G="\[\033[0;32m\]"    # green
local Y="\[\033[0;33m\]"    # yellow
local B="\[\033[0;34m\]"    # blue
local M="\[\033[0;35m\]"    # magenta
local C="\[\033[0;36m\]"    # cyan
local W="\[\033[0;37m\]"    # white

# emphasized (bolded) colors
local EMK="\[\033[1;30m\]"
local EMR="\[\033[1;31m\]"
local EMG="\[\033[1;32m\]"
local EMY="\[\033[1;33m\]"
local EMB="\[\033[1;34m\]"
local EMM="\[\033[1;35m\]"
local EMC="\[\033[1;36m\]"
local EMW="\[\033[1;37m\]"

# background colors
local BGK="\[\033[40m\]"
local BGR="\[\033[41m\]"
local BGG="\[\033[42m\]"
local BGY="\[\033[43m\]"
local BGB="\[\033[44m\]"
local BGM="\[\033[45m\]"
local BGC="\[\033[46m\]"
local BGW="\[\033[47m\]"

local UC=$W                 # user's color
[ $UID -eq "0" ] && UC=$R   # root's color

PS1="$TITLEBAR ${EMK}[${UC}\u${EMK}@${UC}\h ${EMB}\${NEW_PWD}${EMK}]${UC}\\$ ${NONE}"
# without colors: PS1="[\u@\h \${NEW_PWD}]\\$ "
# extra backslash in front of \$ to make bash colorize the prompt

}

init it by setting PROMPT_COMMAND

PROMPT_COMMAND=bash_prompt_command bash_prompt unset bash_prompt

References

↑ BASH Shell change the color of my shell prompt under Linux or UNIX
↑ PROMPT_COMMAND from Bash prompt howto
↑ Color bash prompt code taken from the official Arch Linux wiki

External links

Setting shell options

Jump to navigation Jump to search

← Changing bash prompt • Home • Setting system wide shell options →

Task: Make changes to your bash shell environment using set and shopt commands.
The set and shopt command controls several values of variables controlling shell behavior.

Bash structured language constructs

Jump to navigation Jump to search

← Chapter 4: Conditionals Execution (Decision Making) • Home • Test command →

You can use the if command to test a condition. For example, shell script may need to execute tar command only if a certain condition exists (such as backup only on Friday night).

If today is Friday execute tar command otherwise print an error message on screen.

1More About Logic
- 1.1But What Is A Condition?
  - 1.1.1So, How Do I Make One?
  - 1.1.2Examples

More About Logic

So far, the script you've used followed sequential flow:

#!/bin/bash echo "Today is $(date)" echo "Current directory : $PWD" echo "What Users Are Doing:" w

Each command and/or statement is executed once, in order in above script.
With sequential flow scripts, you cannot write complex applications (intelligent Linux scripts).
However, with if command you will be able to selectively run certain commands (or part) of your script.
You can create a warning message and run script more interactively using if command to execute code based on a condition.

But What Is A Condition?

A condition is nothing but an expression that evaluates to a boolean value (true or false).
In other words condition can be either true or false.
A condition is used in shell script loops and if statements.

So, How Do I Make One?

A condition is mainly a comparison between two values. Open a shell prompt (console) and type the following command:

echo $(( 5 + 2 ))

Sample Output:

Addition is 7. But,

echo $(( 5 < 2 ))

Sample Output:

Answer is zero (0). Shell simple compared two number and returned result as true or false. Is 5 is less than 2? No. So 0 is returned. The Boolean (logical data) type is a primitive data type having one of two values

True
False

In shell:

0 value indicates false.
1 or non-zero value indicate true.

Examples

Operator

Example

Description

True / False

Evaluates To

5 > 12

echo $(( 5 > 12 ))

Is 5 greater than 12?

No (false)

5 == 10

echo $(( 5 == 10 ))

Is 5 equal to 10?

No (false)

5 != 2

echo $(( 5 != 2 ))

5 is not equal to 2?

Yes (true)

1 < 2

echo $(( 1 < 2 ))

Is 1 less than 2?

Yes (true)

5 == 5

echo $(( 5 == 5 ))

Is 5 equal to 5?

Yes (true)

Now, it makes no sense to use echo command for comparisons. But, when you compare it with some value it becomes very useful. For example:

if [ file exists /etc/resolv.conf ] then make a copy else print an error on screen fi

List currently configured shell options

Type the following command:

set -o

Sample outputs:

allexport off braceexpand on emacs on errexit off errtrace off functrace off hashall on histexpand on history on ignoreeof off interactive-comments on keyword off monitor on noclobber off noexec off noglob off nolog off notify off nounset off onecmd off physical off pipefail off posix off privileged off verbose off vi off xtrace off

See set command for detailed explanation of each variable.

How do I set and unset shell variable options?

To set shell variable option use the following syntax:

set -o variableName

To unset shell variable option use the following syntax:

set +o variableName

Examples

Disable which is used to logout of a login shell (local or remote login session over ssh).

set -o ignoreeof

Now, try pressing [CTRL-d] Sample outputs:

Use "exit" to leave the shell.

Turn it off, enter:

set +o ignoreeof

shopt command

You can turn on or off the values of variables controlling optional behavior using the shopt command. To view a list of some of the currently configured option via shopt, enter:

shopt shopt -p

Sample outputs:

cdable_vars off cdspell off checkhash off checkwinsize on cmdhist on compat31 off dotglob off execfail off expand_aliases on extdebug off extglob off extquote on failglob off force_fignore on gnu_errfmt off histappend off histreedit off histverify off hostcomplete on huponexit off interactive_comments on lithist off login_shell off mailwarn off no_empty_cmd_completion off nocaseglob off nocasematch off nullglob off progcomp on promptvars on restricted_shell off shift_verbose off sourcepath on xpg_echo off

How do I enable (set) and disable (unset) each option?

To enable (set) each option, enter:

shopt -s optionName

To disable (unset) each option, enter:

shopt -u optionName

Examples

If cdspell option set, minor errors in the spelling of a directory name in a cd command will be corrected. The errors checked for are transposed characters, a missing character, and one character too many. If a correction is found, the corrected file name is printed, and the command proceeds. For example, type the command (note /etc directory spelling):

cd /etcc

Sample outputs:

bash: cd: /etcc: No such file or directory

Now, turn on cdspell option and try again the same cd command, enter:

shopt -s cdspell cd /etcc

Sample outputs:

/etc [vivek@vivek-desktop /etc]$

Customizing Bash environment with shopt and set

Edit your ~/.bashrc, enter:

vi ~/.bashrc

Add the following commands:

Correct dir spellings

shopt -q -s cdspell

Make sure display get updated when terminal window get resized

shopt -q -s checkwinsize

Turn on the extended pattern matching features

shopt -q -s extglob

Append rather than overwrite history on exit

shopt -s histappend

Make multi-line commandsline in history

shopt -q -s cmdhist

Get immediate notification of background job termination

set -o notify

Disable [CTRL-D] which is used to exit the shell

set -o ignoreeof

Disable core files

ulimit -S -c 0 > /dev/null 2>&1

How do I setup environment variables?

Simply add the settings to ~/.bashrc:

Store 5000 commands in history buffer

export HISTSIZE=5000

Store 5000 commands in history FILE

export HISTFILESIZE=5000

Avoid duplicates in hisotry

export HISTIGNORE='&:[ ]*'

export PAGER=less

Set vim as default text editor

export EDITOR=vim export VISUAL=vim export SVN_EDITOR="$VISUAL"

Oracle database specific

export ORACLE_HOME=/usr/lib/oracle/xe/app/oracle/product/10.2.0/server export ORACLE_SID=XE export NLS_LANG=$($ORACLE_HOME/bin/nls_lang.sh)

Set JAVA_HOME

export JAVA_HOME=/usr/lib/jvm/java-6-sun/jre

Add ORACLE, JAVA and ~/bin bin to PATH

export PATH=$PATH:$ORACLE_HOME/bin:$HOME/bin:$JAVA_HOME/bin

No need to input password again ever

/usr/bin/keychain $HOME/.ssh/id_dsa source $HOME/.keychain/$HOSTNAME-sh

Turn on Bash command completion

source /etc/bash_completion

MS-DOS / XP cmd like stuff

alias edit=$VISUAL alias copy='cp' alias cls='clear' alias del='rm' alias dir='ls' alias md='mkdir' alias move='mv' alias rd='rmdir' alias ren='mv' alias ipconfig='ifconfig'

Other Linux stuff

alias bc='bc -l' alias diff='diff -u'

get updates from RHN

alias update='yum -y update'

set eth1 as default

alias dnstop='dnstop -l 5 eth1' alias vnstat='vnstat -i eth1'

force colorful grep output

alias grep='grep --color'

ls stuff

alias l.='ls -d .* --color=tty' alias ll='ls -l --color=tty' alias ls='ls --color=tty'

Test command - Linux Bash Shell Scripting Tutorial Wiki

Previousinfosec Nextautomation