Bash

Links

• Homepage

• http://www.linuxdoc.org/HOWTO/Bash-Prog-Intro-HOWTO.html
• Bash Guide for Beginners
• http://www.ling.helsinki.fi/users/reriksso/unix/shell.html
• Advanced Bash Scripting Guide
• Linux Shell Scripting Tutorial
• Aliens Bash Tutorial

• Change colour of bash prompt

Keyboard shortcuts

• Shortcuts to move faster in Bash command line
• http://www.skorks.com/2009/09/bash-shortcuts-for-maximum-productivity/
• Bash Keyboard Shortcuts

Tips and tricks

Check if script is running as root

if [ $EUID -eq 0 ];then

Globbing

Globbing except strings

GLOBIGNORE="*.error.log"

String manipulation

Remove character from string

VERSION='2.3.3'
echo "${VERSION//.}"

Replace all characters in a string

Replace all x,y,z with _:

"${var//+([xyz])/_}"

requires extended pattern matching

shopt -s extglob

check if var contains substring

if [[ "$foo" =~ ".*sub.*" ]]

get first character of a string

FIRST=${STRING:0:1}

Date manipulation

Age of a file

stat -C %Y $FILE

read without while loop

The problem is scope, try

echo foo bar | { read a b;echo $b; }

check if variable is integer

if [[$foo =~ ^[0-9]+$]]

 

 

move cursor

^b move back 1 char
^f move forward 1 char
alt-b move back 1 word
alf-f move forward 1 word

loops

loop through range of numbers

for i in {0..10};do echo $i;done

or with variable

M=10
for i in $(seq 0 $M);do echo $i;done

exit while loop

break

 

skip one in loop

continue

bash history timestamp

HISTTIMEFORMAT="%y/%m/%d %T "

screen and bash history

To make sure all screens write to same history (at least on CentOS and RHEL):

echo "history -a;history -r" > /etc/sysconfig/bash-prompt-screen
chmod +x /etc/sysconfig/bash-prompt-screen

In general:

export PROMPT_COMMAND='history -n'

or

export PROMPT_COMMAND="history -a; history -c; history -r; ${PROMPT_COMMAND}"

add extensions to filenames

find . -type f |while read i;do if ! $i =~ .*.txt;then mv -v $i $i.txt;fi;done

 

bash functions

function foo() {
   echo "one: $1 two: $2"
 }
foo "first param" 2

convert units

function convertunits() {

       C="$1"
       U="$2"
       debug "converting $C $U"
       case $U in
               "KiB") O=$((C*1000)) ;;
               "MiB") O=$((C*1000*1000)) ;;
               "GiB") O=$((C*1000*1000*1000)) ;;
               "TiB") O=$((C*1000*1000*1000*1000)) ;;
               *) O="convert error in $U" ;;
       esac
       if [ -z "$O" ];then O="convert_error for unit $U";fi
       echo "$O"

}

Check if disk is mounted

mountpoint /mnt/foo

Get local IP address

ip route get 1 | awk '{print $NF;exit}'

Find depth of a directory

find /foo -type d | awk -F"/" 'NF > max {max = NF} END {print max}'

List only directories

ls -d */

Small random number

echo $((RANDOM/100+1))

FAQ

unary operator expected

try qouting your vars

failing I-search backward

When stuck at that, try

^g

bash: printf: 60.29: invalid number

Check $LC_NUMERIC

Variable scope in while loop

N=0
shopt -s lastpipe
foo | while read i
do
 N=$((N+1))
etc
done
echo $N