FreeKB - Linux Commands sed (replace string)
Linux Commands - sed (replace string)

Let's say that foo contains a value of Hello World.

foo="Hello World"


The sed command with the s (substitue) option can be used to performs a replacment in a file or a variable.

In this example, the text "Hello" will be replaced with the text "Hi". When the -i flag is not used, the change will not actually be made. In this way, this is a sort of test that can be used to see the change, but not commit the change.

echo $foo | sed 's|Hello|Hi|'
. . .
Hi World


With this syntax, Hello will be replaced with Hi in the foo variable.

foo=$( sed "s|Hello|Hi|" <<< "$foo" )


This does the same.

foo=$( echo "$foo" | sed "s|Hello|Hi|" )


Replace multiple instances of a string (global)

If a variable contains more than one occurence of a string, the g (global) option will need to be used to change every instance of the string. For example, let's say a foo contains the following text.

Hello World
Hello World
Hello World"


If the g (global) flag is not used, only the first instance of the word Hello will be changed.

~]# echo $foo | sed 's/Hello/Hi/'
Hi World
Hello World
Hello World


The g (global) flag will change every instance of Hello to Hi.

~]# echo $foo | sed 's/Hello/Hi/g'
Hi World
Hi World
Hi World


Multiple different replacements

In this example, Hello becomes Hi and World becomes Earth, in a single inline command.

echo $foo | sed 's|Hello|Hi|; s|World|Earth|'
. . .
Hi Earth


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