# Remove the third line in the file
    perl -i.bak -ne 'print unless $. == 3' file

    # Remove any lines that contain foo
    perl -i.bak -ne 'print unless /foo/' file

    # Remove foo from all lines
    perl -i.bak -pe 's/foo//g' file

    # Substitute foo with bar on all lines
    perl -i.bak -pe 's/foo/bar/g' file