On Feb 24 17:01, LLoyd via Cygwin wrote: > Hello. > > I'll try to keep this short: > In Cygwin only, using bash 5.2.21-1 or 5.2.15-3 (the only 5.* versions > available), "empty" in a regular expression is not properly matched > and breaks the regular expression. > It's not a quoting issue, I also tested with: > reg='foo|'; [[ foo =~ $regex ]] > > GNU bash, version 5.2.15(3)-release (x86_64-pc-cygwin) > GNU bash, version 5.2.21(1)-release (x86_64-pc-cygwin) > [[ foo =~ foo| ]] (is false, should be true) > [[ foo =~ foo|a ]] (is true) > [[ '' =~ foo| ]] (is false, should be true) > > GNU bash, version 5.1.16(1)-release (x86_64-pc-linux-gnu) > GNU bash, version 5.2.21(1)-release (x86_64-pc-linux-gnu) > [[ foo =~ foo| ]] (is true) > [[ foo =~ foo|a ]] (is true) > [[ '' =~ foo| ]] (is true)
This isn't actually a bug in Cygwin's bash, but a characteristic of the underlying FreeBSD-based regex library. Per POSIX, empty branches in a regular expression are undefined. Quoting from the Open Group: The <vertical-line> is special except when used in a bracket expression (see 9.3.5 RE Bracket Expression). A <vertical-line> appearing first or last in an ERE, or immediately following a <vertical-line> or a <left-parenthesis>, or immediately preceding a <right-parenthesis>, produces undefined results. (https://pubs.opengroup.org/onlinepubs/9799919799/basedefs/V1_chap09.html#tag_09_04_03) Funny enough, even `man 7 regex' contains a description along the lines of POSIX: A (modern) RE is one(!) or more nonempty(!) branches, separated by '|'. It matches anything that matches one of the branches. (https://man7.org/linux/man-pages/man7/regex.7.html) Given that, empty branches are an extension of GLibC which are not necessarily supported by other libs. Corinna -- Problem reports: https://cygwin.com/problems.html FAQ: https://cygwin.com/faq/ Documentation: https://cygwin.com/docs.html Unsubscribe info: https://cygwin.com/ml/#unsubscribe-simple
