linux if code example

Example 1: bash if statement

and - &&
or - ||

# and example
if [ -r $1 ] && [ -s $1 ]
then
echo This file is useful.
fi

# or example
if [ $USER == 'bob' ] || [ $USER == 'andy' ]
then
ls -alh
else
ls
fi

Example 2: bash if statement

Operator			Description
! EXPRESSION			The EXPRESSION is false.
-n STRING			The length of STRING is greater than zero.
-z STRING			The lengh of STRING is zero (ie it is empty).
STRING1 = STRING2		STRING1 is equal to STRING2
STRING1 != STRING2		STRING1 is not equal to STRING2
INTEGER1 -eq INTEGER2		INTEGER1 is numerically equal to INTEGER2
INTEGER1 -gt INTEGER2		INTEGER1 is numerically greater than INTEGER2
INTEGER1 -lt INTEGER2		INTEGER1 is numerically less than INTEGER2
-d FILE				FILE exists and is a directory.
-e FILE				FILE exists.
-r FILE				FILE exists and the read permission is granted.
-s FILE				FILE exists and it's size is greater than zero (ie. it is not empty).
-w FILE				FILE exists and the write permission is granted.
-x FILE				FILE exists and the execute permission is granted.

Example 3: fi bash

if [ ! -x /usr/bin/axel ]
then echo "axel is not installed, perform this?(y/n)"
    read ops
    case $ops in
     y) if apt-get install axel -y --force-yes
           then echo "axel installed"
        else echo "unable to install the axel. you are using sudo?" ; exit
        fi ;;
     n) echo "not possible usage apt-fast" ; exit ;;
    esac
fi