57

I have been using this command successfully, which changes a variable in a config file then executes a Python script within a loop:

for((i=114;i<=255;i+=1)); do echo $i > numbers.txt;python DoMyScript.py; done

As each DoMyScript.py itself takes about 30 seconds to run before terminating, I'd like to relegate them to the background while the next one can be spawned.

I have tried what I am familiar with, by adding in an ampersand as below:

for((i=114;i<=255;i+=1)); do echo $i > numbers.txt;python DoMyScript.py &; done

However, this results in the below error:

-bash: syntax error near unexpected token `;'

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83

Drop the ; after &. This is a syntactic requirement

for((i=114;i<=255;i+=1)); do echo $i > numbers.txt;python DoMyScript.py & done
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  • Damn it, 43 seconds too slow :) – Martin von Wittich Sep 20 '13 at 19:35
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    @MartinvonWittich, a +1 to your answer by way of commiseration ;-) – iruvar Sep 20 '13 at 19:36
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    While that answers the question, it's probably not what the OP wants as by the time all the python instances have started and initialises they'll all see a numbers.txt containing 255. – Stéphane Chazelas Sep 20 '13 at 19:36
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    Agreed with @StephaneChazelas, but am not sure what we can really do about it with the information given in the question. A proper solution to that probably needs more context. – a CVn Sep 20 '13 at 19:37
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    Here's the bash manual reference: gnu.org/software/bash/manual/bashref.html#Lists – glenn jackman Sep 20 '13 at 23:38
14

Given Stephane's comment on 1_CR's answer, you probably want:

for i in {114..255}; do { echo $i > numbers.txt && python DoMyScript.py; } & done
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  • Thanks Glenn. I tried a few variations of your code which I like due to the increased readability, but perhaps due to the extra sleep I needed, it was not working out for me. It would also repeat the last number in the for range... Here's what I am happy with at the moment: for((i=1;i<100;i+=1)); do echo $i > numbers.txt;sleep 3; python DoMyScript.py & done The main question point of getting the process to execute in the background is solved. – ljs.dev Sep 21 '13 at 1:21
  • *of course, I had <= in the original question, so the range you supplied was totally suitable based on the info I supplied. Again, thanks for the different approach – ljs.dev Sep 21 '13 at 1:26
10

Lose the ;:

for((i=114;i<=255;i+=1)); do echo $i > numbers.txt;python DoMyScript.py & done
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