Parameter Substitution in Bash

1. Use Parameter Substitution in Linux Bash
2. Remove Expression From String in Bash
3. Replace Expression in String in Bash

Sometimes we may want to delete a value from a string or replace it with a new one. There are many different ways to do this.

This article will explain how to use the parameter substitution method in Linux Bash scripting for this purpose.

Use Parameter Substitution in Linux Bash

Bash parameter substitution is an excellent way to remove or replace values from a string. The rest of the article will explain how we can do them with examples.

The following string will be used for examples.

str="one two three two one"

Remove Expression From String in Bash

There are two methods for deleting the expression from a string with the parameter substitution.

The ${string%expression} command removes the expression at the end of the string. The last one in the str will be deleted in the example below.

echo "${str%one}"

The ${string#expression} command removes the expression at the beginning of the string. The first one in the str will be deleted in the following example.

echo "${str#one}"

Replace Expression in String in Bash

The ${string/expression/value} command replaces the first expression it finds in the string with the value. The first one in the str will be replaced with four in the example below.

echo "${str/one/four}"

The ${string//expression/value} command replaces all the expression it finds in the string with the value. In the following example, all the one words in the str will be replaced with the four.

echo "${str//one/four}"

The ${string/#expression/value} command replaces the expression at the beginning of the string with the value. The first one in the str will be replaced with four in the example below.

echo "${str/#one/four}"

The ${string/%expression/value} command replaces the expression at the end of the string with the value. The last one in the str will be replaced with four in the following example.

echo "${str/%one/four}"