regex negative numbers

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

Hi monks, this script accepts two numbers and prints the range. When I allow a negative for the first number it works:

#!/usr/bin/perl

while (<>) {
        print if m!(^-{0,1}\d*)\s+(\d*)!m;
        print "$_\n" for ($1 .. $2);
        }

But when I allow both to be negative it doesn't:

#!/usr/bin/perl

while (<>) {

        print if m!(^-{0,1}\d*)\s+(^-{0,1}\d*)!m;
        print "$_\n" for ($1 .. $2);
        }
[download]

Could a blessed monk point out my folly please? Thanks for all the replies to my previous question (esp. dws) and TIA for this one. Jono

Comment on regex negative numbers Download Code

Replies are listed 'Best First'.
Re: regex negative numbers by bjelli (Pilgrim) on Aug 28, 2002 at 08:13 UTC
To summarize: the problem is in the pattern, (or in the fact that you didn't check if the pattern mached at all). I've changed three things about the pattern: ? instead of {0,1} ^ just once \d+ instead of \d* discarded the /m at the end `while (<DATA>) { chomp; print "Test case '$_'\n"; if ( m!^(-?\d+)\s+(-?\d+)! ) { print "$_, " for ($1 .. $2); } else { print "doesn't match"; } print "\n\n"; } __DATA__ 1 6 -4 6 -4 -1 6 1 6 -4 -1 -4` [download] making the program count backwards is left as an exercise to the reader. -- Brigitte 'I never met a chocolate I didnt like' Jellinek http://www.horus.com/~bjelli/ http://perlwelt.horus.at	[reply] [d/l]
Re: regex negative numbers by theorbtwo (Prior) on Aug 28, 2002 at 06:50 UTC
You didn't watch what you were doing when you copy-and-pasted. Your second regex contains two ^ assertations... in other words, you required the string to begin two sepperate places. (There are circumstances where it is kosher to have two ^s in a regex -- to whit, where there can be nothing between them, or where one is optional. Oh, or if you use the approprate modifer (/m, IIRC, but my memory is bad), ^ will match after a newline as well as at the begnning of the string). Read perlre for more info on regexes. Confession: It does an Immortal Body good.	[reply]
Re: regex negative numbers by hotshot (Prior) on Aug 28, 2002 at 06:37 UTC
first, you can use '?' instead of '{0,1}'. secondly, that works for me (I'v check this): `while (<>) { print if /^(-?\d+)\s+(-?\d+)/; print $_ for ($1..$2); }` [download] , Hotshot	[reply] [d/l]
Re: regex negative numbers by Django (Pilgrim) on Aug 28, 2002 at 06:51 UTC
What you're probably trying to do is this: `while (<>) { / ( ^ -? \d+ ) \s+ # optional minus at start of line, some digits, some space ( -? \d+ ) # same thing, but NOT at start of line /x # eXplanation mode (m is useless when you read line by line) and print; # I didn't get the purpose of your print statements - # this one will simply print the line if matched. }` [download]	[reply] [d/l]