Call a command line which includes both "echo" and "|"

Question

I tried to use Python to call the command line to execute some files. However, when there is a command line containing both echo and |, the subprocess.call seems not working very well. Like when I run:

echo "perp -t ../data/ReviewTest.text" | ./eva -b ../data/6.binlm

I will get what I want. However, when I try this:

import subprocess
e=["echo","\"perp", "-t", "../data/R.text\"", "|", "./eva", "-b", "../data/6.binlm"]
subprocess(e)

I will get everything except echo showed in command line like:

".prep -t ..data/ReviewTest.text" | ./eva -b ../data/6.binlm

It seems that in subprocess.call(), when there is an echo, everything after it will just be thrown out onto the command line.

I hope there is some solution for me to use subprocess when a command contains both echo and |.

score 3 · Accepted Answer · edited Dec 03 '17 at 00:46

3

I think this might achieve the effect you are looking for (it should reproduce exactly the first command line listed in your question):

>>> import subprocess
>>> e = 'echo "perp -t ../data/ReviewTest.text | ./eva -b ../data/6.binlm'
>>> subprocess.call(e, shell=True)

"|" is a shell meta-character, so you need to invoke subprocess.call with shell=True.
In the command line, you are passing the string "perp -t ../data/ReviewTest.text" as the first and only argument of echo, so you need to pass the same string and not just individual components in the subprocess.call argument string.

edited Dec 03 '17 at 00:46

ekhumoro

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answered Feb 26 '13 at 22:30

isedev

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Is it possible to do with shell=False? – parthiban Dec 20 '16 at 06:38
@oarthiban no, the shell is required to interpret the pipe meta-character '|' – isedev Dec 28 '16 at 17:55

score 1 · Answer 2 · answered Feb 26 '13 at 22:29

The pipe | is a shell construct meaning that the command needs to be run as input to a shell. This means setting shell=True when subprocess.call() is called.

import subprocess
subprocess.call("""echo "perp -t ../data/ReviewTest.text" | ./eva -b ../data/6.binlm""", shell=True)

There are notes about using shell=True in the Python docs.

Call a command line which includes both "echo" and "|"

2 Answers2