sed command line tool

The sed command line tool allows you to pipe a string of text and substitute part of it.

Note that it does for the first occurrence only:

$ echo "my, this is my sentence" | sed 's/my/My/'
My, this is my sentence

Escaping forward slashes with the backslashes:

$ echo "convert /usr/local/bin to /common/bin" | sed "s/\/usr\/local\/bin/\/common\/bin/"
convert /common/bin to /common/bin

$ echo "Repeat me 5 times." | sed 's/[0-9]/& & & & &/'

Repeat me 5 5 5 5 5 times.