I want to mksquashfs a chroot, and include the /cdrom dir, but exclude everything inside it. I already know how to do this with -wildcards, but I want to see if -regex has a bug. Test case:
cd $(mktemp -d)
mkdir -p cdrom cdrom2/why
mksquashfs . /tmp/chroot.squashfs -info -noappend -regex -e '^cdrom/.*$'
The problem is that cdrom2/why was omitted! It seems to me like "/" is actually ignored there. Is this a mksquashfs bug?
This is because you don't fully understand how regexes work in Mksquashfs exclude files.
An exclude file if wildcards are used is basically treated as series of wildcarded files separated by slashes (/), i.e. wildcard1/wildcard2/wildcard3, will match wildcard1 against the top level directory, wildcard2 against the subdirectory and so on.
Specifying -regex simply replaces wildcard matching with regex matching. It is still evaluated as regexes separated by slashes (/), i.e. regex1/regex2/regex3.
In your example the regex "^cdrom" is evaluated against the files in the top level directory, and matches both "cdrom" and "cdrom2".
If you wanted the regex to only match "cdrom" you should use
mksquashfs . /tmp/chroot.squashfs -info -noappend -regex -e '^cdrom$/.*'