Where can I test Bash POSIX ERE patterns interactively?

POSIX ERE is also used by tools such as grep -E, egrep, awk, sed -E, and several database regex operators. A playground aimed at any of those tools can be useful, but check whether it uses the same implementation and whether it reproduces Bash quoting and word-splitting behavior.

Bash’s =~ operator uses the system’s POSIX ERE implementation through regcomp. That means behavior can vary slightly between systems, such as glibc and musl. A Bash shell playground like JDoodle can be useful because it tests the expression in an actual Bash script, including Bash’s parsing rules. Remember that spaces in the regex may need to be escaped or quoted.

Regex101 now includes an ERE-compatible flavor through its Boost option, so it may work for many tests. For the most reliable result, run the final pattern in Bash itself, since the shell parses the right-hand side before the regex engine sees it.

Most online testers default to PCRE, which supports features that POSIX ERE does not. For example, use [0-9] or [[:digit:]] instead of d, and avoid non-capturing groups, lazy quantifiers, lookarounds, named groups, and similar PCRE extensions. Search for testers that specifically advertise POSIX ERE support; rsyslog’s regex tester and RegexTester are possible options, though their exact behavior should be verified.