I have a file that has the word "snake" in it

There is a snake in the first line.
No such word in the second line.
Another snake in the 3rd line.
There is a blue snake and a red snake here.

This one-liner that you can run on the command line will replace the word "snake" by the word "camel" in the file:

$ perl -i -p -e 's/snake/camel/g' snakes_or_camels.txt

This one-liner will create a backup of the original file before making the changes.

$ perl -i.bak -p -e 's/snake/camel/g' snakes_or_camels.txt

• -i means "inplace editing"
• -i.bak means "copy to .bak then inplace editing"
• -p means (in rough terms) "What ever you do, do it on every line of data."
• -e means "execute the following code".
• s/snake/camel/g is a substitution. The g at the end means globally. Without that only the first snake would be replaced.

The result is

There is a camel in the first line.
No such word in the second line.
Another camel in the 3rd line.
There is a blue camel and a red camel here.

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