You can use tr///c to replace all characters other than space and tab to something, and then use index to search for that character. 
#!/usr/bin/perl
use warnings;
use strict;

sub regex_pos {
    my ($string) = @_;
    $string =~ /[^ \t]/g;
    return pos($string) - 1
}

sub tr_pos {
    my ($string) = @_;
    (my $tr = $string) =~ tr/ \t/!!/c;
    return index $tr, '!'
}

for my $s ("  \t x  ", "\t\t\t\t\t\t                  \xff...\t ") {
    regex_pos($s) == tr_pos($s) or die;
}

use Benchmark qw{ cmpthese };

my $s = ' ' x 200 . "\t" x 200 . "\x01" . " " x 200;
cmpthese(-3, {
    regex => sub { regex_pos($s) },
    tr    => sub { tr_pos($s)    },
});

[download]

On my machine, it seems about 3 times faster than regex in 5.26.1: 

          Rate regex    tr
regex 316530/s    --  -67%
tr    954355/s  202%    --

[download]

but only marginally faster in blead perl: 

          Rate regex    tr
regex 896519/s    --   -6%
tr    954359/s    6%    --

[download]

map{substr$_->[0],$_->[1]||0,1}[\*||{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]

In reply to Re: opposite of index+rindex? How-to? Needed? by choroba
in thread opposite of index+rindex? How-to? Needed? by perl-diddler

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