Python subprocess and shell input redirection

Question

On a unix command line I can do:

paste <(echo A) <(echo B)

However, when I try to do this:

import subprocess
subprocess.call('paste <(echo A) <(echo B)', shell = True)

I get this error:

/bin/sh: -c: line 0: syntax error near unexpected token `('
/bin/sh: -c: line 0: `paste <(echo A) <(echo B)'

Is it not possible to do shell input redirection with the subprocess module?

That's probably running /bin/sh as your shell which doesn't do that. You need to try to force it to use /bin/bash. — Etan Reisner
– Etan Reisner, Commented Sep 18, 2014 at 11:23
Thanks Etan! I added executable='/bin/bash' and it worked! Will you leave an answer? — tommy.carstensen
– tommy.carstensen, Commented Sep 18, 2014 at 11:24
have you given the os.system('paste <(echo A) <(echo B)') a try..? — Zuko
– Zuko, Commented Sep 18, 2014 at 13:04
Olu, that one fails as well. The subprocess docs reads: "This module intends to replace several older modules and functions: os.system" — tommy.carstensen
– tommy.carstensen, Commented Sep 18, 2014 at 14:17

Etan Reisner · Accepted Answer · 2014-09-18 12:59:36Z

1

Many things by default use /bin/sh as the shell of choice. /bin/sh is often not bash.

The /bin/sh on your system most likely does not support process substitution.

Convince subprocess.call to use /bin/bash as the shell instead and it should work.

answered Sep 18, 2014 at 12:59

Etan Reisner

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2 Comments

Thank you again. This did the trick: subprocess.call('paste <(echo A) <(echo B)', shell = True, executable='/bin/bash')

@tommy.carstensen: even /bin/bash if called using name /bin/sh may use different compatibility mode i.e., no process substitutions.