Python output to be read inside bash script line by line

Question

Basic idea here is to call 1 file from the asd directory and 1 line from the output.txt file in each curl call:

#!/bin/bash
python MJD.py -> output.txt
FILES=/home/user/asd/*
for f in $FILES
do
filename="$output.txt"
while read -r line
do
curl -F ID='zero' -F dir="@$f" -F TIME="$line" -F outputFormat=json "http://blabla"
done
done

This code actually calls the python script and saves the output inside the output.txt file. The output file is just 1 number on each line for several lines. Now what I want to do is to get, starting from the first line, for -F TIME=" one value inside the text file".

I don't know what part of my code is causing the problem. When I call this script the part calling the files from dir works but for every time the TIME=0 appears on screen, looks like nothing is read from the output.txt file.. What am I missing here?

Community · Accepted Answer · 2020-06-20 09:12:55Z

2

This would be a good place for a process substitution and exec:

#!/bin/bash

exec 4< <( python MJD.py - )
# now, the output from the python script can be read from channel 4

for file in /home/user/asd/*; do
    IFS= read -u4 -r time              # get the next line from MJD.py
    curl -F ID='zero' -F dir="@$file" -F TIME="$time" -F outputFormat=json "http://blabla"
done

That exec "trick" is specified in the manual:

exec [-cl] [-a name] [command [arguments]]

[...] If no command is specified, redirections may be used to affect the current shell environment.

edited Jun 20, 2020 at 9:12

CommunityBot

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answered Jul 17, 2017 at 21:48

glenn jackman

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1 Comment

NapolyoN Over a year ago

Thank you! Now everything works like a charm. I understood the idea but I should look into that manual and learn more about this. Again, thanks a lot!

zwer · Accepted Answer · 2017-07-17 20:59:06Z

0

You're not feeding your inner loop the output file, try:

#!/bin/bash
python MJD.py > output.txt
FILES=/home/user/asd/*
for f in $FILES
do
filename="output.txt"
while read -r line
do
curl -F ID='zero' -F dir="@$f" -F TIME="$line" -F outputFormat=json "http://blabla"
done < "$filename"
done

Although, since you're already using Python, why not just write all the logic in Python and deal with everything at one place?

answered Jul 17, 2017 at 20:59

zwer

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1 Comment

NapolyoN Over a year ago

I have understood the situation here and corrected it now it works. However, it goes for all values to all values. There are 2 files in the dir path and there are 2 values in the txt file. When this code works it applies everyone 1 by 1 creates 4 results.. What I need is only 2 results 1 entry from dir and 1 line from the txt starting from first and goes until they finish for the first time so only 2 results and once it done the loop to stop.

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