Support BSD expr in startup script

[neirbowj]

Jetty version(s)

All supported versions.

Enhancement Description

When the startup script reads the config file to detect XML files, it uses the expr command to skip comment lines. The only non-comment entry in the default config file starts with a hyphen. expr on Linux, macOS, and probably elsewhere, does not care.

$ expr "--module=pid,state" : "#"
0

expr on FreeBSD complains.

expr "--module=pid,state" : "#"
expr: illegal option -- -
expr: usage: expr [-e] expression

Both implementations recognize the use of "--" to signal the end of the command line options so that subsequent arguments that begin with a hyphen are not treated as options. This works on Linux and BSD:

$ expr -- "# comment" : "#"
1
$ expr -- "--module=pid,state" : "#"
0

[joakime]

Done, will be available in next releases of Jetty 10.0.20 / 11.0.20 / 12.0.6 (due at end of month)