Regex Tagging (newbie)

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

This should be a simple task, but I've not had any luck getting it to work.

I wish to change the string:

Sat May 5 02:29:11 2001

Into

May 5 02:29:11

Regex is certainly not a stong point of mine and I've never attempted to use tagging before.

my $now = time;

$log_start=scalar localtime $now -1 * 86400;
print "Log start = $log_start\n";

$log_start=~ /\w (\w\s+\d+\s\w)\s\d+/i;
print "Modified Log start = $log_start\n";
[download]

This yeilds:

Use of uninitialized value in concatenation (.) at.....

Where am I going wrong here ?

Comment on Regex Tagging (newbie) Download Code

Replies are listed 'Best First'.
(ar0n) Re: Regex Tagging (newbie) by ar0n (Priest) on May 05, 2001 at 15:52 UTC
I'm not sure what you mean by 'tagging', but here goes it: `$log_start =~ s/^\w+\s+(\w+\s+\d{1,2}\s+\d{1,2}:\d{1,2}:\d{1,2})\s+\d{ +4}$/$1/i; print $log_start, "\n";` [download] The reason it wasn't working, was because your `\w` will only match 1 character, and no more. Not only that, you try to match the date which - if it were successful - it would save into `$1`, which you don't seem to be assigning to anything. I don't think `Use of uninitialized value in concatenation (.) at.....` [download] has anything to do with the code you posted above, since there no actual concatenations taking place. At least, running the snippet with `-w` doesn't yield me any warnings. update modified regex slightly (added +'s). it works now. [ ar0n ]	[reply] [d/l] [select]
Re: (ar0n) Re: Regex Tagging (newbie) by cajun (Chaplain) on May 05, 2001 at 16:15 UTC
Thanks ar0n. I see your point about the \w. I've also tried printing $1. So the regex isn't matching. I replaced mine with yours. `my $now = time; $log_start=scalar localtime $now -1 * 86400; print "Log start = $log_start\n"; $log_start=~ s/^\w+\s+(\w+\s\d{1,2}\s\d{1,2}:\d{1,2}:\d{1,2})\s\d{4}$/ +$1/i; print "Modified Log start = $1\n";` [download] update Thanks to ar0n in CB, the correct regex is: `$log_start=~ s/^\w+\s+(\w+\s+\d{1,2}\s\d{1,2}:\d{1,2}:\d{1,2})\s\d{4}$ +/$1/i;` [download]	[reply] [d/l] [select]
Re: Regex Tagging (newbie) by mincus (Chaplain) on May 05, 2001 at 16:15 UTC
If the day that you wanna remove is alway first, you could also use split. `$log_start="Sat May 5 02:29:11 2001"; ($throw_away, @temp)=split(/ /,$log_start); $log_start=join(" ",@temp); print $log_start.$/;` [download] best of luck! .mincus telnet://bbs.mincus.com	[reply] [d/l]
Re: Regex Tagging (newbie) by Daddio (Chaplain) on May 05, 2001 at 16:45 UTC
You can also make this a whole lot simpler, since that date string is a constant format. `$date =~ s/^\w+\s+(.*?)\s+\d+$/$1/;` Same concept, just a little shorter! -- D a d d i o	[reply] [d/l]
(crazyinsomniac) Re: Regex Tagging (newbie) by crazyinsomniac (Prior) on May 06, 2001 at 04:32 UTC
Fixed-format string manipulation using a regex is overkill. (unless you just wanna exercise) `#!/usr/bin/perl -w use strict; my $str = 'Sat May 5 02:29:11 2001'; substr($str,0,4,''); substr($str,-4,4,''); print $str;` [download] update `#This will also do in case you don't have 4 param substr (i forgot abo +ut that) $str = 'Sat May 5 02:29:11 2001'; substr($str,0,4) = ''; substr($str,-4,4) = '';` [download] ___crazyinsomniac_______________________________________ `Disclaimer: Don't blame. It came from inside the void` `perl -e "$q=$_;map({chr unpack qq;H;,$_}split(q;;,qH*));print;$q/$q;"`	[reply] [d/l] [select]