Perl open external command with custom filehandles

Question

Is there a perl function, either built in, or in a library that is like the following:

run(IN_FILEHANDLE, OUT_FILEHANDLE, ERR_FILEHANDLE, $cmd);

Which gets the external command to read from IN_FILEHANDLE, write to OUT_FILEHANLE, with stderr going to ERR_FILEHANDLE.

e.g.

run(STDIN, STDOUT, STDERR, $cmd);

Will be similar to:

system($cmd);

And:

run(IN, OUT, ERR, $cmd);

Will be a bit like a non-existant version of:

open(IN, OUT, ERR, "|$cmd|");

I find open($fh, "|$cmd");, and open($fh, "$cmd|"); easy to use, I just read/write from the filehandle. I just want one that works both ways.

Bonus points if one can also optionally read/write to a scalar instead.

I've been mucking around with open3 and IPC::Run but I can't seem to get them to work. Working example (perhaps with say grep) would be appreciated.

Edit: In response to comment, my current code:

open3($stdin_fh, $stdout_fh, $stderr_fh, $refresh_exec); #1
print "Opened"; #2
print $stdin_fh "Input to command\n"; #3

seems to hang before reaching line #2

and using IPC::Run:

start \@cmd_arr, $stdin_fh, $stdout_fh, $stderr_fh;
print "Opened"; #2
print $stdin_fh "Input to command\n"; #3

Runs the command but writes gives the error: Can't use an undefined value as a symbol reference.

I know my code is incomplete, but I don't want to paste 400 lines of code, and if I could successfully cut it down and isolate the problem I wouldn't need to ask the question.

I'm even unsure whether open3 or IPC::Run do what I want, so I'm just looking for a working solution I can build on.

Why don't you show the code you're using with `run3` and explain exactly what's not working? — Mat, May 02 '13 at 07:19
Yes. Edited. There were actually many lines of input in my code. Like I said, a working example would be helpful. — Clinton, May 02 '13 at 09:14

score 0 · Answer 1 · edited May 23 '17 at 12:18

0

I would:

Redirect STD* to the desired FH's.
Execute system($cmd);
Restore STD* to their original state.

Have a look at Hari's example for detailed approach:

https://stackoverflow.com/a/1720592/1485996

You may also use local to avoid restoring STD.

edited May 23 '17 at 12:18

Community

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answered May 02 '13 at 12:44

Mattan

733
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Can you show an example of how this allows me to `print` directly to `$cmd`s input like when using `open($fh, "|$cmd")`? – Clinton May 02 '13 at 14:41

Perl open external command with custom filehandles

1 Answers1