HACKTUX notes from the trenches

Bash supports various string operations. Here are some examples to get you started quickly. For detailed information, see the official Bash documentation.

String Assignment

Below are a few ways to assign a string variable.

bash$ OS=Linux

Use quotes to encapsulate strings with spaces:

bash$ OS='CentOS 4.6'

Or, use double quotes to allow for variable expansion:

bash$ DISTRO="Fedora"
bash$ OS="$DISTRO Linux"
bash$ echo $OS
Fedora Linux

String Length

Determining the length of your string is easy:

bash$ PROG="Bash"
bash$ echo ${#PROG}
4

You can also use expr:

bash$ expr length $PROG
4

Substring Extraction

Below are some examples of substring expansion in the form of ${string:position} and ${string:position:length}. String indexing starts at zero!

bash$ PROG="Bash"
bash$ echo ${PROG:0}
Bash
bash$ echo ${PROG:1}
ash
bash$ echo ${PROG:1:2}
as

Testing Strings

Test if a string is of length 0

[ -z $STRING ]

Test if length of string is not zero:

[ ! -z $STRING ]
[ -n $STRING ]

Test if strings are equal.

[ $STRING1 == $STRING2 ]

Remember to use quotes if the string has spaces or escape characters (newlines).

[ "$STRING1" == "$STRING2" ]

The 'not equal; operator is !=

[ $STRING1 != $STRING2 ]