Test Operators

💡 The following only work on strings and not values of integers. It will treat numbers as plain text strings.

String Test operators	Meaning
`[[ $string1 = $string2 ]] ; echo $?`	compares two strings and will exit 0 (success) if they are the same. Other languages compare using “==” or “===”
`[[ $string1 != $string2 ]] ; echo $?`	compares two strings and will exit 1 (fail) if they are the same. This `!=` is pretty common throughout other languages.
`[[ -z $some_variable ]] ; echo $?`	tests if a string is empty, this is commonly used to see if a file exists or not. If it’s null or “none” then it will return an exit of 0.
`[[ -n $some_variable ]] ; echo $?`	Does the opposite of the -z operator in that it will exit 1 if $some_variable is null or “none”. (It’s checking to see if the string is not empty)

File Test operators	Meaning
`[[ -e $file_name ]] ; echo $?`	This operator will exit 0 if the file specified “exists” or not.
`[[ -f $file_name ]] ; echo $?`	This operator checks to see if a file exists and will exit 0 if the specified file is a “file” and not a directory. If it’s a directory it will exit 1
`[[ -d $file_name ]] ; echo $?`	This operator checks to see if a file exists and will exit 0 if the parameter passed is a directory.
`[[ -x $file_name ]] ; echo $?`	This operator checks to see if a file exists and will exit 0 if the file specified has executable permissions.
`[[ -r $file_name ]] ; echo $?`	This operator checks to see if a file exists and will exit 0 if the file specified has readable permissions.
`[[ -w $file_name ]] ; echo $?`	This operator checks to see if a file exists and will exit 0 if the file specified has writable permissions.
`[[ $file_name1 -nt $file_name2 ]] ; echo $?`	This operator checks to see if a file exists and will exit 0 if the file specified is newer than.