Table of Contents

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

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