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Check numeric variable

tlep -  
Hello,

I'm trying in Perl to check if a variable passed as an argument to a script is numeric.

I successfully tested:
if ($ARGV[2] =~ m/^\d+$/){print "Argument '".$ARGV[2]."' is numeric.\n";}

However, I'm unable to use NOT (to get the opposite):

if (!$ARGV[2] =~ m/^\d+$/){print "Argument '".$ARGV[2]."' is not numeric.\n";}
=> doesn't work
if ($ARGV[2] !=~ m/^\d+$/){print "Argument '".$ARGV[2]."' is not numeric.\n";}
=> doesn't work
if !($ARGV[2] =~ m/^\d+$/){print "Argument '".$ARGV[2]."' is not numeric.\n";}
=> doesn't work

Thank you :-) 
Configuration: Windows XP Firefox 2.0.0.11

7 answers

  1. b0rice
    Hello,

    the negation in a regexp in Perl is: $string !~ m/$re/;

    In your case:

    print 'Argument '.$ARGV[2].' non-numeric' if ($ARGV[2] !~ m/^\d+$/);

    You could also do:

    print "Argument ".$ARGV[2];
    if ( $ARGV[2] =~ m/^\d+$/ ) {
    print " numeric\n";
    }
    else {
    print " alphanumeric\n";
    }

    just simply ;)
    1
    1. Char Snipeur Contributor
      Salut.
      I don't understand why 
      if (!$ARGV[2] =~ m/^\d+$/){print "Argument '".$ARGV[2]."' non numérique.\n";}
      doesn't work. Is it due to operator precedence? Would 
      if (!($ARGV[2] =~ m/^\d+$/)){print "Argument '".$ARGV[2]."' non numérique.\n";}
      work? Otherwise, I'm really confused, the not on a boolean should always work normally.
      --
      Best regards! I used to believe, now I am sure.Jesus Christ
      Char Snipeur
      0
      1. lami20j Moderator
        Hello,

        here are some tests
        root@debian:~# perl -e 'print "non-numeric\n" if ("aaa" !~ /^\d+$') non-numeric root@debian:~# perl -e 'print "non-numeric\n" if (!("aaa" =~ /^\d+$/))' non-numeric root@debian:~# perl -e 'print "non-numeric\n" unless ("aaa" =~ /^\d+$/)' non-numeric

        --
        106485010510997108
        0
        1. lami20j Moderator
          ou
           perl -e '"aaa"=~/^\d+$/?"":print "non numérique\n"'

          --
          106485010510997108
          0
          2. lami20j Moderator
            Another possibility to test non-numeric is with the complemented character class \D that looks for non-numeric characters 
            root@debian:~# perl -e 'print "non-numeric\n" if ("aaa" =~ /^\D+$/)' non-numeric
            this way I don't need to negate
            I simply look for a non-numeric match

            --
            106485010510997108
            0
            1. lami20j Moderator
              For the info

              !~ it's not quite a negation

              this operator rather means to find the non-match and not to not find the match
              --
              106485010510997108
              0
              1. Char Snipeur Contributor
                Thank you for the clarification.
                --
                Greetings! I used to believe, now I am certain.Jesus Christ
                Char Sniper
                0