many of my programs, when run with redirected I/O, and during a special part of running (the last phase) need access to the original standard file descriptors. so what i have been doing is duplicating 0,1,2 to 3,4,5 in the redirector script. now, i am starting to convert these from bash to python. the first one is basically a simple thing that redirects stdout to a file. there are other that i will get to next that do many other things. these ultimately get run by the very same programs that will be run by the redirectors.
here is the first one i an trying to convert ... in bash:
the output of line 17 always goes the same way as the command output (line 18).
how could having
i have many others of these things, each doing many different kinds of redirection, most also doing the 0,1,2 -> 3,4,5 fd duplicating, some in bash, some in C, and even a few in ksh, and they all work. i intend to eventually convert them all to python3.
i am running python version 3.5.2.
here is the first one i an trying to convert ... in bash:
#!/bin/bash [[ "$#" -gt 1 ]] || exit 3 o="$1" shift if [[ "$#" -lt 1 ]];then exec cat >"$o" elif [[ -e "$o" && ! -w "$o" ]];then echo "o: file '$o' not writable" 1>&2 exit 6 fi exec 3<&0 exec 4>&1 exec 5>&2 exec "$@" 1>"$o"here is what i first put together in python:
#!/usr/bin/env python3 """o: set stdout to file and run commad.""" from os import dup2 from subprocess import Popen from sys import argv,stdout argv.pop(0) if not argv: exit(1) n=argv.pop(0) if not argv: argv=['cat'] try: with open(n,'w') as f: dup2(0,3) dup2(1,4) dup2(2,5) print('woot',file=f) r=Popen(argv,stdout=f).wait() except: r=1 exit(r)line 17 is just there for debugging. i am expecting the output of the command starting in atgument 2 to be written the file named in argument 1. but it is coming out to the stdout given to it by the shell it is being run from (and nothing is written to the file). if i comment out line 14 then it works as expected, except that stdin wouldn't be duplicated to fd 3.
the output of line 17 always goes the same way as the command output (line 18).
how could having
os.dup2(0,3)
in there cause stdout to fail to be redirected to the file?i have many others of these things, each doing many different kinds of redirection, most also doing the 0,1,2 -> 3,4,5 fd duplicating, some in bash, some in C, and even a few in ksh, and they all work. i intend to eventually convert them all to python3.
i am running python version 3.5.2.
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What do you call someone who speaks three languages? Trilingual. Two languages? Bilingual. One language? American.
What do you call someone who speaks three languages? Trilingual. Two languages? Bilingual. One language? American.