How do I search and replace across multiple lines with Perl?

Question

$ perl --version
This is perl, v5.10.1 (*) built for x86_64-linux-gnu-thread-multi

$ echo -e "foo\nbar" > baz.txt
$ perl -p -e 's/foo\nbar/FOO\nBAR/m' baz.txt
foo
bar

How can I get this replacement to work?

Answer 1

You can use the -0 switch to change the input separator:

perl -0777pe 's/foo\nbar/FOO\nBAR/' baz.txt

-0777 sets the separator to undef, -0 alone sets it to \0 which might work for text files not containing the null byte.

Note that /m is needless as the regex does not contain ^ nor $.

Answer 2

It has to do with the -p switch. It reads input one line at a time. So you cannot run a regexp against a newline between two lines because it will never match. One thing you can do is to read all input modifying variable $/ and apply the regexp to it. One way:

perl -e 'undef $/; $s = <>; $s =~ s/foo\nbar/FOO\nBAR/; print $s' baz.txt

It yields:

FOO
BAR