As illustrated here and detailed in “this question“, the function fnmatch() is involved to interpret glob patterns, which means regular expressions are not supported.
This is what gitignore
man page mentions:
Otherwise,
git treats the pattern as a shell glob suitable for consumption by fnmatch(3)
with theFNM_PATHNAME
flag: wildcards in the pattern will not match a/
in the pathname.
For example, “Documentation/*.html
” matches “Documentation/git.html
” but not “Documentation/ppc/ppc.html
” or “tools/perf/Documentation/perf.html
“.
You can see some correspondence between glob patterns and regular expressions in those questions.