Using BRE and ERE in awk

Question

How does awk distinguish between use of BRE versus ERE ? For sed there is the -E option one can use.

Answer 1

It does not need to distinguish between the two since regular expressions in awk are always POSIX extended regular expressions.

From the POSIX specification for awk:

The awk utility shall make use of the extended regular expression notation [...]

I'm not aware of any awk implementation that introduces a non-standard option for switching to POSIX basic regular expressions.

The sed utility always uses POSIX basic regular expressions unless you use it with its (so far) non-standard but fairly commonly available -E option. The grep utility also defaults to POSIX basic regular expressions, but the -E option that enables it to use POSIX extended regular expressions is actually standard (while -P for Perl-compatible regular expressions, PCRE, is non-standard and not commonly implemented on non-GNU systems). The grep utility can additionally interpret the given expressions as plain strings with its standard -F option.