Re: [PATCH v4] [GSOC]trailer: pass arg as positional parameter

Junio C Hamano [off-list ref] 于2021年3月31日周三 上午1:14写道：

ZheNing Hu [off-list ref] writes:

quoted

The `prepare_shell_cmd()` in "run-command.c" seem to use "$@" to pass
shell args.

Yes. "$@" is a way to write "$1" "$2" "$3"...
Since you are passing only one,

        echo "$@"

and

        echo "$1"

would be the equivalent.

I am not sure what program you fed to the gdb (and remote debugging
over e-mail is not my forte ;-), but let's see.

quoted

Before exec:

(gdb) print argv.v[1]
$22 = 0x5555558edfd0 "/bin/sh"
(gdb) print argv.v[2]
$23 = 0x5555558f4c80 "-c"
(gdb) print argv.v[3]
$24 = 0x5555558ed4b0 "echo \"123\" \"$@\""
(gdb) print argv.v[4]
$25 = 0x5555558f5980 "echo \"123\""
(gdb) print argv.v[5]
$26 = 0x5555558edab0 "abc"
(gdb) print argv.v[6]
$27 = 0x0

Some unexpected things happened here.
Maybe "abc" was wrongly used as the parameter of "echo"?
Looking forward to your reply.

Observe

        $ sh -c '
                echo "\$0 == $0"
                count=0
                for arg in "$@"
                do
                        count=$(( $count + 1 ))
                        echo "\$$count == $arg"
                done
        ' 0 1 2
        $0 == 0
        $1 == 1
        $2 == 2

i.e. the first arg after

        argv[1] = "/bin/sh"
        argv[2] = "-c"
        argv[3] = "script"

is used to give the script the name of the program ($0).  Are we
getting hit by this common confusion?

It is customery to write such an invocation with '-' as the "name of
the program" thing, so that ordinary positional parameters are
available starting at $1, not $0, like so:

        sh -c 'script' - arg1 arg2 ...

The configuration is like this:
trailer.bug.key=BUG:
trailer.bug.ifexists=add
trailer.bug.cmd=echo "123"

And use:

$ git interpret-trailers --trailer="bug:456" --trailer="bug:789"<<-EOF
EOF

BUG: 123
BUG: 123 456
BUG: 123 789

I just want three "BUG: 123", but "456" and "789" appeared...

In fact, I think about this problem like this way:
When we execute a child process that runs the shell,
the function`prepare_shell_cmd()` will actively add "$@" to the end of our
shell command when we have more than zero args ,

e.g.

"echo \"123\"" "abc"

will turn to

 "echo \"123\" \"$@\"" "echo \"123\"" "abc"

Normally, $@ should not cause any problems because it passes arguments
to the script what we provide.

But now, what we actually want is take any $1 that appears in the script as an
argument, the automatically added $@ causes $1 to be implicitly included.
And the original $ARG does not have this problem, Or if we pass environment
variables, this kind of problem will not occur.

Or If we want to avoid this problem, should we add one new options in
`struct child_process` , such as: "shell_no_implicit_args" , let git not add
 extra "$@" before we run the shell script?

Thanks.

--
ZheNing Hu