Two line match

jrosenfeld has asked for the wisdom of the Perl Monks concerning the following question:

Hi, I have been trying to get a regular expression to match over two lines. Here is my input data:

ghjghjgkhgkghj

-----

fsgdfgsdfgdfsgdsfg

I would like the regular expression to match the two lines of "----" and convert them to one.

So that the result would be:

ghjghjgkhgkghj

-----

fsgdfgsdfgdfsgdsfg

I would also like it to convert multiple lines of ----- to 1 line.

I have tried :

s/-----\n-----/------/g

and many variations, but nothing has been successful. Thank You, Jeff

Comment on Two line match

Replies are listed 'Best First'.
Re: Two line match by moritz (Cardinal) on Mar 10, 2008 at 15:14 UTC
`s/-----\n-----/------/g` or `s/-----\n+-----/------/g` both should work, but only if you have both lines in `$_`. If you read your files with a standard loop like this: `while (<>)[ # substition here }` [download] it can never work, because there's only one line in $_ when you run the substition.	[reply] [d/l] [select]
Re^2: Two line match by jrosenfeld (Initiate) on Mar 10, 2008 at 15:21 UTC
I am trying to do it as a one-liner on the command line using cat foo.txt \| perl -p -e 's/-----\n-----/------/g' and it does not do anything. Is there a problem with multiple lines and command-line matching? Jeff	[reply]
Re^3: Two line match by moritz (Cardinal) on Mar 10, 2008 at 15:25 UTC
The `-p` option enables line-by-line processing, so you have to change perls notion of a line: `perl -pe 'BEGIN { $/ = undef }; s/---\n---/---/g;'` [download]	[reply] [d/l] [select]
Re^4: Two line match by jrosenfeld (Initiate) on Mar 10, 2008 at 15:38 UTC
Re^5: Two line match by moritz (Cardinal) on Mar 10, 2008 at 15:43 UTC
Re^3: Two line match by grizzley (Chaplain) on Mar 10, 2008 at 16:12 UTC
use -0 to read whole file at once: `cat foo.txt \| perl -p0 -e 's/-----\n\n-----/------/g'` [download]	[reply] [d/l]
Re^4: Two line match by jrosenfeld (Initiate) on Mar 10, 2008 at 16:47 UTC
Re^5: Two line match by grizzley (Chaplain) on Mar 10, 2008 at 18:17 UTC
Re: Two line match by toolic (Bishop) on Mar 10, 2008 at 15:25 UTC
`#!/usr/bin/env perl use warnings; use strict; my $prev = 0; while (<DATA>) { if (/-----/) { print unless $prev; $prev = 1; } else { print; $prev = 0; } } __DATA__ aaaaaaaaaaaa ----- ----- bbbbbbbbbbbb ----- ----- ----- ccccccccccccc` [download] Prints: `aaaaaaaaaaaa ----- bbbbbbbbbbbb ----- ccccccccccccc` [download]	[reply] [d/l] [select]
Re^2: Two line match by jrosenfeld (Initiate) on Mar 10, 2008 at 15:46 UTC
That works except that it only converts two lines of ----- into one. I wanted it to be able to convert any number of lines of ----- ------ ------> into 1 line of it. Shouldn't the /g do that? Jeff	[reply]
Re^3: Two line match by toolic (Bishop) on Mar 10, 2008 at 16:10 UTC
My code converts 2 consecutive lines of 5 dashes into one line of 5 dashes (between the line of "a"'s and the line of "b"'s). My code also converts 3 consecutive lines of 5 dashes into one line of 5 dashes (between the line of "b"'s and the line of "c"'s). You can add any arbitrary number of lines of 5 dashes, and they will all be converted to one line of 5 dashes. I guess I do not understand your question afterall.	[reply]
Re: Two line match by NetWallah (Canon) on Mar 10, 2008 at 16:07 UTC
Here is a one-liner you can try. Interchange quotes(' vs ") if on Linux: `perl -ne "next unless /ghjghjgkhgkghj/../fsgdfgsdfgdfsgdsfg/;chomp;pus +h @l,$_;END{$r=join '', @l[1..$#l-1];print $r}" Your-file-name-here` [download] Note the use of the flip-flop operator .. to select stuff between the tokens, and array slicing to avoid the delimiters. "As you get older three things happen. The first is your memory goes, and I can't remember the other two... " - Sir Norman Wisdom	[reply] [d/l]
Re^2: Two line match by jrosenfeld (Initiate) on Mar 10, 2008 at 20:45 UTC
Thank you for all of the help	[reply]
Re: Two line match by olus (Curate) on Mar 10, 2008 at 15:15 UTC
You have two line breaks between the '-----' lines, because you have an empty line in the middle (or so it seems). Your regexp should account for two \n and not only one.	[reply]