Running bash script with for cycle as a Python subprocess in background

Question

I have a bash script with a for cycle in it called test.sh:

#!/bin/sh
echo -n > "/path/output.txt"
for i  in {1..10}
do 
echo "Test" >> "/path/output.txt"
done

I would like to run it in background while the instruction of the Python script are performed. I am using Python subprocess:

import subprocess
subprocess.Popen('test.sh')

I can't get any output or the output is written in "output.txt" only once.

You probably also want echo -n "" or something, unless you want a literal -n written to that file. If you just want to create the file, try touch. — meatspace
– meatspace, Commented Jan 5, 2017 at 19:17
@meatspace if I use touch I can't overwrite the file if it is already exist — G M
– G M, Commented Jan 9, 2017 at 9:32

chepner · Accepted Answer · 2017-01-05 18:59:42Z

2

Generally, don't use brace expansions with loops. The shell has to expand the entire expression before you can iterate over it. Either use a C-style for loop (in shells like bash that support it):

for ((i=1; i<=10; i++)); do
    ...
done

or use a while loop (in any POSIX-compatible shell):

i=1
while [ "$i" -le 10 ]; do
    ...
    i=$((i+1))
done

answered Jan 5, 2017 at 18:59

chepner

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2 Comments

G M Over a year ago

Sorry: while [ $i -le 10] do i=$(( $i + 1)). Ok, I guess they are both rigtht

chepner Over a year ago

The arguments can only be integers in an arithmetic context, so identifiers are automatically dereferenced.

Harald Nordgren · Accepted Answer · 2017-01-05 18:28:32Z

0

for i in {1..10}

is not valid syntax for sh. You tagged you question with Bash, so replace the first line with

#!/bin/bash

answered Jan 5, 2017 at 18:28

Harald Nordgren

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