bash

Header

!/bin/bash

Variables

Assignment X=“hello” note that there should be no space on either side of the equals sign Referring to echo $X

Conditionals

if [ condition ] then statements else more statements fi

Operators

^ Operator ^ Meaning ^ | -eq | Integer equality | | -neq | Integer inequality | | -lt | Integer less than | | -le | Integer less than or equal to | | -gt | Integer greater than | | -ge | Integer greater than or equal to | | = | String equality | | != | String Inequality | | -n | Non empty string | | -z | Empty string | | -d | Directory existence test | | -f | File existence test |

Iteration

Iterate over files and print their names: for i in $(ls); do echo $i; done

Iterate over .zip files and extract them for i in $(ls *.zip); do unzip $i; done

Examples

Accepting input The following bash script accepts a parameter or prompts for the value if it is not supplied. For the sake of the example, it simply echos this to STDOUT

!/bin/bash

MYVAR="" if [ -z $1 ] then echo Enter a value: read MYVAR else MYVAR=$1 fi echo $MYVAR

Useful Links

• http://www.cyberciti.biz/faq/bash-for-loop/

Andrew McDonough is a consultant CTO and software developer, currently based between Berlin and London.

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