How to search and replace text within a text file using the Command Line on Linux

This can be accomplished by using the sed command.

sed =  stream editor for filtering and transforming text

For this example we will have a file called test.txt that contains the following text “This is a test file with some test information, containing some test data.“

We want to replace all instances of test in the file with cool and save the output to a new file called cool.txt

To accomplish this open a new command line window and type and execute the following command:

sed -e 's/test/cool/g' test.txt > cool.txt

-e =  add the script to the commands to be executed
s = s/regexp/replacement/
Attempt  to match regexp against the pattern space.  If success‐
ful,  replace  that  portion  matched  with  replacement.    The
replacement may contain the special character & to refer to that
portion of the pattern space  which  matched,  and  the  special
escapes  \1  through  \9  to refer to the corresponding matching
sub-expressions in the regexp.
g = Copy/append hold space to pattern space.

If you view cool.txt by using the cat command

cat cool.txt

you’ll see the following output

This is a cool file with some cool information, containing some cool data.

To learn more about the set command type in man sed in the command line

man sed