bad regex! no cookie!

match-time.sh

#!/bin/sh

a5=aaaaa
a27="$a5$a5$a5$a5$a5"aa
aq5='a?a?a?a?a?'
aq27="$aq5$aq5$aq5$aq5$aq5"'a?a?'

pattern="$aq27$a27"
input="$a27"

printf 'Pattern: "%s"\nInput: "%s"\n' "$pattern" "$input"

printf 'Testing grep:\n'
time printf '%s\n' "$input" | grep -oE -e "^$pattern"

printf 'Testing perl:\n'
time perl -E 'say "match" if $ARGV[1] =~ m/^$ARGV[0]/' "$pattern" "$input"

printf 'Testing python:\n'
time python3 -c 'import sys; import re; print(re.match(sys.argv[1], sys.argv[2]))' "$pattern" "$input"

It returns 'match' for up to 18 a's after the a?'s. Probably a limitation to avoid RE exploits.

Yes, my bad. It's not returning 0 (no match), but false (error). The error is PCRE_BACKTRACK_LIMIT_ERROR http://www.php.net/manual/en/function.preg-last-error.php