Re: opposite of index+rindex? How-to? Needed? (updated)

... what is the index of the first non-space character?

c:\@Work\Perl\monks>perl -wMstrict -le
"my $s = '    a     ';
 ;;
 $s =~ m{ \S }xms;
 print $-[0];
"
4
[download]

... as long as it didn't invoke the regex engine.

What's the point of that?

Update: More generally:

c:\@Work\Perl\monks>perl -wMstrict -le
"my $s = 'xyzzyBARxkcdFOOyz';
 ;;
 my $vowel = qr{ [AEIOUaeiou] }xms;
 ;;
 print qq{offset of first vowel: }, $s =~ m{ ($vowel) }xms ? $-[1] : '
+none';
 ;;
 print qq{offset of last vowel: }, $s =~ m{ .* ($vowel) }xms ? $-[1] :
+ 'none';
 ;;
 print qq{offset of first vowel: }, 'XYZ' =~ m{ ($vowel) }xms ? $-[1] 
+: 'none';
"
offset of first vowel: 6
offset of last vowel: 14
offset of first vowel: none
[download]

See @- @+ in perlvar.

Give a man a fish: <%-{-{-{-<

Comment on Re: opposite of index+rindex? How-to? Needed? (updated) Select or Download Code

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Re^2: opposite of index+rindex? How-to? Needed? (updated) by rsFalse (Chaplain) on Sep 02, 2019 at 00:26 UTC
And alternatively with look-ahead: `;; print qq{offset of first vowel: }, $s =~ m{ (?= $vowel ) }xgms ? pos +$s : 'none'; ;; print qq{offset of last vowel: }, $s =~ m{ .* (?= $vowel ) }xgms ? po +s $s : 'none';` [download] Note 'g' modifier. To negate, one can use negative look-ahead `(?! $vowel )`. Upd. Not really! Look at the AnomalousMonk reply.	[reply] [d/l] [select]
Re^3: opposite of index+rindex? How-to? Needed? (updated) by AnomalousMonk (Archbishop) on Sep 02, 2019 at 06:44 UTC
... with look-ahead ... `$+[0]` also works here (note `$+[0]` vice `$-[1]` and no `/g` modifier): `c:\@Work\Perl\monks>perl -wMstrict -le "my $vowel = qr{ [AEIOUaeiou] }xms; ;; my $s = 'xyzzyBARxkcdFOOyz'; ;; print 'offset of first vowel: ', $s =~ m{ (?= $vowel) }xms ? $+[0] : +'none'; print 'offset of last vowel: ', $s =~ m{ .* (?= $vowel) }xms ? $+[0] +: 'none'; print 'offset of first vowel: ', 'XYZ' =~ m{ (?= $vowel) }xms ? $+[0] + : 'none'; " offset of first vowel: 6 offset of last vowel: 14 offset of first vowel: none` [download] I like the look-ahead idea because it avoids a capture and so may be slightly faster. To negate, one can use negative look-ahead (?! $vowel ). I think there's a problem here: `c:\@Work\Perl\monks>perl -wMstrict -le "my $vowel = qr{ [AEIOUaeiou] }xms; ;; my $s = 'aePDQioVWXua'; ;; print 'offset of first non-vowel: ', $s =~ m{ (?! $vowel) }xmsg ? pos +($s) : 'none'; print 'offset of last non-vowel: ', $s =~ m{ .* (?! $vowel) }xmsg ? p +os($s) : 'none'; ;; $s = 'aei'; print 'offset of first non-vowel: ', $s =~ m{ (?! $vowel) }xmsg ? pos +($s) : 'none'; " offset of first non-vowel: 2 offset of last non-vowel: 12 offset of first non-vowel: 3` [download] The second and third cases give questionable results because there's always a place in a string where a negative look-ahead will succeed if it is true nowhere else: just beyond the end of the string. (`$+[0]` has the same problem in these cases as pos.) Update: However, a positive look-ahead to a negated char class works: `c:\@Work\Perl\monks>perl -wMstrict -le "my $non_vowel = qr{ [^AEIOUaeiou] }xms; ;; my $s = 'aePDQioVWXua'; ;; print 'offset of first non-vowel: ', $s =~ m{ (?= $non_vowel) }xmsg ? + pos($s) : 'none'; print 'offset of last non-vowel: ', $s =~ m{ .* (?= $non_vowel) }xmsg + ? pos($s) : 'none'; ;; $s = 'aei'; print 'offset of first non-vowel: ', $s =~ m{ (?= $non_vowel) }xmsg ? + pos($s) : 'none'; " offset of first non-vowel: 2 offset of last non-vowel: 9 offset of first non-vowel: none` [download] The positive assertion requires that something be present, so the overall match can fail. (`$+[0]` works as well as `pos`.) Give a man a fish: `<%-{-{-{-<`	[reply] [d/l] [select]