How make open function use bash instead of sh?

Question

I want to use bash instead of sh when I use the open function. For instance:

sub run_cmd {
    my ($cmd) = @_;
    my $fcmd;

    print("Run $cmd\n");

    open($fcmd, "$cmd |");
    while ( my $line = <$fcmd> ) {
        print "-> $line";
    }
    close $fcmd;
}

eval{run_cmd('ps -p $$')};

Here, the output is:

Run ps -p $$
->    PID TTY          TIME CMD
-> 189493 pts/6    00:00:00 sh

We can see sh is used by default.

I have some constraints and I need (1) to use the open function and (2) to call bash instead of sh. I tried simply to add bash at the beginning of my command but it doesn't work:

Run ps -p $$
/bin/ps: /bin/ps: cannot execute binary file

What can I do to use bash with the open function?

A related question that may help you: [Which shell does a Perl system() call use?](https://stackoverflow.com/q/4225102/7939871) — Léa Gris, Oct 09 '20 at 11:00
@Pierre : Aside from the correct answer given by tripleee, the error you see comes probably from an incorrect setting of the `PATH` environment variable. I suggest that, for testing, you print its value before running the command. — user1934428, Oct 09 '20 at 11:06
@user1934428 No, putting `bash` immediately in front will simply cause `bash` to try to execute `ps` as a script file. — tripleee, Oct 09 '20 at 15:14
@tripleee - Right, I should have read the error message properly. Or course the `-c` is missing. — user1934428, Oct 11 '20 at 07:40

tripleee · Answer 1 · 2020-10-09T15:12:24.360

5

You can explicitly run bash instead.

open($fcd, "bash -c '$cmd' |");

The other answer indeed shows some important best practices for when cmd is not completely trivial, or not under your control.

edited Oct 09 '20 at 15:12

answered Oct 09 '20 at 10:37

tripleee

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That will still call `sh -c` to run the `bash -c` (because of the single quotes). – Oct 09 '20 at 15:10

score 4 · Accepted Answer · answered Oct 09 '20 at 14:56

Don't take your chances with quote injections:

open my $fcmd, '-|', qw(bash -c), $cmd;

(Also notice that you don't need to close $fcmd explicitly if you declared it with my; it will be automatically closed at the end of the block; perl is not java ;-))

How make open function use bash instead of sh?

2 Answers2