Match into list?

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

Good Day bros. I was hunting around for some resources to parse Apache log files, and I ran across this script which contains the following statement

  my ($host,$date,$url_with_method,$status,$size,$referrer,$agent) = $
+line =~
          m/^(\S+) - - \[(\S+ \+\d{4})\] "(\S+ \S+ [^"]+)" (\d{3}) (\d
++|-) "(.*?)" "([^"]+)"$/;
[download]

in an attempt to split apart a $line from the log file like

76.172.202.159 - - [31/Aug/2007:15:58:15 -0600] "GET / HTTP/1.1" 200 2
+9692 "http://www.paperbackswap.com/forum/view_topic.php?t=70235&ls=" 
+"Mozilla/5.0 (Macintosh; U; Intel Mac OS X; en-US; rv:1.8.0.12) Gecko
+/20070508 Firefox/1.5.0.12"
[download]

This didn't look right to me since the $line =~ m/.../ part would evaluate to 1 rather than a list. I tried it in the debugger sure enough it didn't work.

This got me to thinking about whether there is a way to make it work. I looks like intent of it is for the parens in the regexp to capture the material of interest, but this would wind up in the special vars $1, $2, etc., rather than a list. Does anyone know how this could be made to work?

Comment on Match into list? Select or Download Code

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Re: Match into list? by Sidhekin (Priest) on Sep 04, 2007 at 00:00 UTC
In list context, the m// operator (without /g modifier) does indeed return a list of all captures. So that's not your problem. One problem with that pattern is that it's insisting on a "+" in the time zone specification. The string you're trying to match has a "-" ... ;-) Use `[+-]` instead of `\+`, and it'll match that string at least (tested). `print "Just another Perl ${\(trickster and hacker)},"` The Sidhekin proves Sidhe did it!	[reply] [d/l] [select]
Re: Match into list? by ysth (Canon) on Sep 03, 2007 at 23:54 UTC
It does indeed work. Somehow you tried something different in the debugger. A regex match returns differently in list vs. scalar context, and with or without /g. See http://perldoc.perl.org/perlop.html#Regexp-Quote-Like-Operators-operator%2c-regexp: "If the /g option is not used, m// in list context returns"...	[reply]
Re^2: Match into list? by cormanaz (Deacon) on Sep 04, 2007 at 00:08 UTC
Taking the debugger out of it, when I run #!/usr/bin/perl -w use strict; my $line = '76.172.202.159 - - [31/Aug/2007:15:58:15 -0600] "GET / HTT +P/1.1" 200 29692 "http://www.paperbackswap.com/forum/view_topic.php?t +=70235&ls=" "Mozilla/5.0 (Macintosh; U; Intel Mac OS X; en-US; rv:1.8 +.0.12) Gecko/20070508 Firefox/1.5.0.12"'; my ($host,$date,$url_with_method,$status,$size,$referrer,$agent) = $li +ne =~ m/^(\S+) - - \[(\S+ \+\d{4})\] "(\S+ \S+ [^"]+)" (\d{3}) (\d+\|-) " +(.*?)" "([^"]+)"$/; print "$host\n$date\n$url_with_method\n$status\n$size\n$referrer\n$age +nt\n"; [download] The output is Use of uninitialized value in concatenation (.) or string at test.pl l +ine 6. Use of uninitialized value in concatenation (.) or string at test.pl l +ine 6. Use of uninitialized value in concatenation (.) or string at test.pl l +ine 6. Use of uninitialized value in concatenation (.) or string at test.pl l +ine 6. Use of uninitialized value in concatenation (.) or string at test.pl l +ine 6. Use of uninitialized value in concatenation (.) or string at test.pl l +ine 6. Use of uninitialized value in concatenation (.) or string at test.pl l +ine 6. [download]	[reply] [d/l] [select]
Re^3: Match into list? by ysth (Canon) on Sep 04, 2007 at 00:37 UTC
Your regex only works with positive tz offsets, not negative :) Remember to always check if your match succeeds before trying to use the results; in list context, this looks like: #!/usr/bin/perl -w use strict; my $line = '76.172.202.159 - - [31/Aug/2007:15:58:15 -0600] "GET / HTT +P/1.1" 200 29692 "http://www.paperbackswap.com/forum/view_topic.php?t +=70235&ls=" "Mozilla/5.0 (Macintosh; U; Intel Mac OS X; en-US; rv:1.8 +.0.12) Gecko/20070508 Firefox/1.5.0.12"'; my ($host,$date,$url_with_method,$status,$size,$referrer,$agent) = $li +ne =~ m/^(\S+) - - \[(\S+ [-+]\d{4})\] "(\S+ \S+ [^"]+)" (\d{3}) (\d+\|-) + "(.?)" "([^"]+)"$/ or warn "match failed!"; print "$host\n$date\n$url_with_method\n$status\n$size\n$referrer\n$age +nt\n"; [download] or: #!/usr/bin/perl -w use strict; my $line = '76.172.202.159 - - [31/Aug/2007:15:58:15 -0600] "GET / HTT +P/1.1" 200 29692 "http://www.paperbackswap.com/forum/view_topic.php?t +=70235&ls=" "Mozilla/5.0 (Macintosh; U; Intel Mac OS X; en-US; rv:1.8 +.0.12) Gecko/20070508 Firefox/1.5.0.12"'; if ( my ($host,$date,$url_with_method,$status,$size,$referrer,$agent) += $line =~ m/^(\S+) - - \[(\S+ [-+]\d{4})\] "(\S+ \S+ [^"]+)" (\d{3}) (\d+\|-) + "(.?)" "([^"]+)"$/ ) { print "$host\n$date\n$url_with_method\n$status\n$size\n$referrer\n +$agent\n"; } else { warn "match failed!"; } [download] You might take a look at the Regexp::Log module.	[reply] [d/l] [select]