Question

I’m having problem with string redirection and python with a shell Ghostscript command.

There is NP executing this:

subprocess.call(["gs", "-q","-dBATCH", "-dNOPAUSE","-sDEVICE=bbox", "input.pdf"])

But I get an error adding 2>&1:

subprocess.call(["gs", "-q","-dBATCH", "-dNOPAUSE","-sDEVICE=bbox", "input.pdf","2>&1"])

Or:

subprocess.call(["gs", "-q","-dBATCH", "-dNOPAUSE","-sDEVICE=bbox", "input.pdf","2>&1",">/dev/null"])

I want to use 2>&1 to apply ‘grep’.

Sample of the error:

Error: /undefinedfilename in (2>&1) Operand stack:

Execution stack: %interp_exit .runexec2 –nostringval–
–nostringval– –nostringval– 2 %stopped_push –nostringval– –nostringval– –nostringval– false 1 %stopped_push Dictionary stack: –dict:1156/1684(ro)(G)–
–dict:1/20(G)– –dict:77/200(L)– Current allocation mode is local Last OS error: 2 GPL Ghostscript 9.05: Unrecoverable error, exit code
1 1

Still remains unsolved how to execute a command like:

subprocess.call("gs -q -dBATCH -dNOPAUSE -sDEVICE=bbox input.pdf 2>&1
| egrep -v HiResBoundingBox | egrep -o "[0-9]{1,}",shell=True)

Answer 1

It’s because you’re passing the arguments as a list. When you pass the arguments as an iterable, each piece is passed to the spawned process (in this case, gs is complaining that it doesn’t know what to do with 2>&1…) You’d probably get the same message if you typed:

gs -q -dBATCH -dNOPAUSE -sDEVICE=bbox input.pdf '2>&1' 

in a shell.

subprocess.call("gs -q -dBATCH -dNOPAUSE -sDEVICE=bbox input.pdf 2>&1",shell=True)

will do what you want — or ‘better’…

import sys
subprocess.call(["gs", "-q", "-dBATCH", "-dNOPAUSE", "-sDEVICE=bbox", "input.pdf"],stderr=sys.stdout)

(better because it sidesteps the security issues with shell=True)