http://www.perlmonks.org?node_id=140214

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

what is a regular expression to match a word containging all and only a set of characters? egs: for the set t,a,b tab should match and bat should match but not bbat or brat!

Replies are listed 'Best First'.
Re: regular xpression stuff
by Masem (Monsignor) on Jan 20, 2002 at 21:00 UTC
    In this case, you don't want a regex, at least directly. I think we've golfed this once, but in general: 
    my $to_be_matched = 'tab';
my $word = 'bat';
if ( join '', sort split(//, $word) eq 
     join '', sort split(//, $to_be_matched ) ) {
   # Success!
} else {
   # Failure
}

    [download]

    Update - $ instead of @ on to_be_matched

    -----------------------------------------------------
    Dr. Michael K. Neylon - mneylon-pm@masemware.com || "You've left the lens cap of your mind on again, Pinky" - The Brain
    "I can see my house from here!"
    It's not what you know, but knowing how to find it if you don't know that's important

[reply]
[d/l]
      shouldnt 
       
if ( join '', sort split(//, $word) eq 
     join '', sort split(//, $to_be_matched ) ) {

      [download]
      be 
      if ( join('', sort split(//, $word)) eq join('', sort split(//, $to_be
+_matched)) ) {

      [download]
      (extra parenthesis added )

      After adding the parenthesis , i get "Success" (i.e. "bat" = "tab" based on your example), without them the result is "Failure"
[reply]
[d/l]
[select]
Re: regular xpression stuff
by Parham (Friar) on Jan 20, 2002 at 21:24 UTC
    this would also work 
    $var = 'bat';
if ($var =~ /^[bat]{3}$/) { print "match"; } else { print "fail"; }

    [download]
    since you want only those letters to exist, check from beginning to end that word for each letter, the {3} should be the number of letters in that word
[reply]
[d/l]
      If I'm understanding the question correctly, this will not work.

      It seems that the inquiring monk wants to match each letter once and only once.
      /^[bat]{3}$/ could match 'ttt', 'bba', 'aaa', etc. If that *is* undesirable, Masem's excellent reply is probably the best way to go.
[reply]
[d/l]
        count0++ i forgot to take that into consideration
[reply]
Re: regular xpression stuff
by Lucky (Scribe) on Jan 20, 2002 at 22:01 UTC
    Looks terrific but works: 
    @to_check=('bat','bbat','brat');
for (@to_check){
 if (/^([bat])(?!\1)([bat])(?!\2)([bat])(?!\3)/){
   # do something
 }
}

    [download]
    Just create regexp dynamically.
[reply]
[d/l]
      if (/^([bat])(?!\1)([bat])(?!\2)([bat])(?!\3)/){</i>

      This does not entirely work, 'bab', for instance, passes the match.

      the following modified version works, but it is not too elegant, just imagine checking a 5 letter word!

      if (/^([bat])(?!\1)([bat])(?!\2|\1)([bat])(?!\3|\2|\1)/){

      [download]

      Will perl for money
      JJ Knitis
      (901) 756-7693
      gt8073a@industrialmusic.com

[reply]
[d/l]
[select]
        For any word: 
        my $set='bat';
my $regexp;
for (my $i=1;$i<=length($set);$i++){
 my $x=join '|', map {"\\$_"} 1..$i;
 $regexp.="([$set])(?!$x)";
}
if (/^$regexp/){
  # do something
}

        [download]
        Terrible... :-)
[reply]
[d/l]

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