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From: weisberg@hpccc.HP.COM (Len Weisberg)
Newsgroups: comp.lang.perl
Subject: how long is a {0,m} match?
Message-ID: <12170008@hpccc.HP.COM>
Date: 2 Aug 90 00:40:08 GMT
Organization: HP Corp Computing & Services
Lines: 98

Here's another bit of confusing regexp behavior:

------------------------------------------------------------------------------
## perl test program:

sub try {
  local($pat, $str) = @_;
  $str =~ /$pat/ ;
  print "\$pat=/$pat/, \t\$str=$str, \t\$&=$&<<\n";
}


&try ( "a+", "aaay");
&try ( "a+", "xaaay");
print "\n";

&try ( "a{1,}", "aaay");
&try ( "a{1,}", "xaaay");
print "-----------------\n";

&try ( "a{1,2}", "aaay");
&try ( "a{1,2}", "xaaay");
print "\n";

&try ( "a{1,4}", "aaay");
&try ( "a{1,4}", "xaaay");
print "-----------------\n";

&try ( "a*", "aaay");
&try ( "a*", "xaaay");
print "\n";

&try ( "a{0,}", "aaay");
&try ( "a{0,}", "xaaay");
print "-----------------\n";

&try ( "a?", "aaay");
&try ( "a?", "xaaay");
print "\n";

&try ( "a{0,1}", "aaay");
&try ( "a{0,1}", "xaaay");
print "-----------------\n";

&try ( "a{0,4}", "aaay");
&try ( "a{0,4}", "xaaay");
print "\n";




-----------------------------------------------------------------------------
results:

$pat=/a+/, 	$str=aaay, 	$&=aaa<<
$pat=/a+/, 	$str=xaaay, 	$&=aaa<<

$pat=/a{1,}/, 	$str=aaay, 	$&=aaa<<
$pat=/a{1,}/, 	$str=xaaay, 	$&=aaa<<
-----------------
$pat=/a{1,2}/, 	$str=aaay, 	$&=aa<<
$pat=/a{1,2}/, 	$str=xaaay, 	$&=aa<<

$pat=/a{1,4}/, 	$str=aaay, 	$&=aaa<<
$pat=/a{1,4}/, 	$str=xaaay, 	$&=aaa<<
-----------------
$pat=/a*/, 	$str=aaay, 	$&=aaa<<
$pat=/a*/, 	$str=xaaay, 	$&=<<

$pat=/a{0,}/, 	$str=aaay, 	$&=aaa<<
$pat=/a{0,}/, 	$str=xaaay, 	$&=<<
-----------------
$pat=/a?/, 	$str=aaay, 	$&=a<<
$pat=/a?/, 	$str=xaaay, 	$&=<<

$pat=/a{0,1}/, 	$str=aaay, 	$&=a<<
$pat=/a{0,1}/, 	$str=xaaay, 	$&=<<
-----------------
$pat=/a{0,4}/, 	$str=aaay, 	$&=aaa<<
$pat=/a{0,4}/, 	$str=xaaay, 	$&=<<

------------------------------------------------------------------------------

If there is some general principle about longest match, 
it seems to break when 0 repetitions match, but only when
the match is not at the start of the string.

Does this make sense?   Is it a bug?

( perl -v gives:
$Header: perly.c,v 3.0.1.5 90/03/27 16:20:57 lwall Locked $
Patch level: 18
     etc...)

Any enlightenment appreciated.
Thanks,

- Len Weisberg - HP Corp Computing & Services - weisberg@corp.HP.COM