For educational purpose ( see ""(??{ code })" section of perlre). In real code, please use KISS_principle if ($x >= 0 && $x <= 100). 
perl -le '
for $num (qw(-1 0 7 12 88 100 123)) {
   if ($num=~ /^(\d+)(??{$^N >=0 && $^N <= 100 ? "" : "(?!)"})$/) {
       print $1;
   }
}
'

[download]
update: added if clause. update2: added perlre reference.
print+qq(\L@{[ref\&@]}@{['@'x7^'!#2/"!4']});

In reply to Re: Matching string containing values between 0 and 100 inclusive by codeacrobat
in thread Matching string containing values between 0 and 100 inclusive by Anonymous Monk

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