How to substitute an environment variable using sed on Linux?

An Environment variable is a dynamic-named value. Generally, these are variables are exported in a single terminal using a command shown below

export $SOMEVARIABLE=value

or they are stored inside the bash files, so that they remain available in all the terminals once the file is sourced. If we want to change an environment variable we can simply change the above command’s value field and then source the file, but if we want to do that with the help of the sed command then we need to know a little bit about the sed command.

Let’s explore the sed command, which is short for stream editor. This command is used to perform different functions like find, replace, insert and many more on a particular file.

Syntax

sed [OPTIONS]... [SCRIPT] [INPUTFILE...]

Example 1

Considering we have a simple text file where we want to replace a string that is present in the file to another string, we can make use of the grep command in that case.

File

immukul@192 linux% cat somefile.txt

this is a test file and it is used for testing and is not available for anything else so
please stop asking, lionel messi

Now we want to replace the string “it” with “litt” in the above file. The command to do that is shown below −

Command

sed ‘s/it/litt’ somefile.txt

Output

immukul@192 linux% cat somefile.txt

this is a test file and litt is used for testing and is not available for anything else so
please stop asking, lionel messi

Now let’s see how to exchange an environment variable’s value inside a bash script with the help of the sed command.

There’s an environment variable TUTS whose value is equal to /Users. In order to change that value in a bash script, we can add these lines to the script.

Script

sed 's@PPP@'"$TUTS"'@'

Now if we run the above script, and type PPP, then instead of printing PPP back, we will be able to print the value of the environment variable.

Output

immukul@192 linux-questions-code % ./sss.sh
PPP
/Users