bash - for loop in command line

Question

Could you please advise , I'm trying to run a "for" loop on a shell command line

for i in `seq 4`; do `wireshark &`; done

From some reason the loop isn't finish and only 1 wireshark window is open

Could you please advise?

Since you'll likely get comments or even answers on that, your loop would be prettier to the modern shell scripter if it was written as for ((i=0; i<4; i++)); do wireshark &; done. That most likely won't fix your problem though — Aaron
– Aaron, Commented Nov 5, 2020 at 15:25
Wireshark needs a GUI and so you won't be able to run it to the background. — Raman Sailopal
– Raman Sailopal, Commented Nov 5, 2020 at 15:30

William Pursell · Accepted Answer · 2020-11-05 15:48:19Z

3

You really don't want to put wireshark & in backticks. The shell that executes your loop creates a subshell to run wireshark and is waiting for that subshell to close all of its open file descriptors that are writing to stdout so that it can collect the data written. (That's what the bacticks do!). If you just want to run wireshark in the background, then this should work:

for ...; do wireshark & done

Note that backticks is pretty ancient syntax, and $() has been preferred since the mid 90s at least. If you're going to use seq you should write it as for i in $(seq 4); do .... You're using bash, so you could do for((i=0; i <4; i++)). There are a lot of ways to do the iteration, but that's not relevant to the issue you're having.

edited Nov 5, 2020 at 15:48

answered Nov 5, 2020 at 15:32

William Pursell

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Arkadiusz Drabczyk · Accepted Answer · 2020-11-05 15:48:59Z

0

You don't need to use seq external command in bash and `wireshark &` is not correct - backticks are used for command substitution but notice that $() is recommended over backticks these days. It should be:

for i in {1..4}; do wireshark & done

answered Nov 5, 2020 at 15:48

Arkadiusz Drabczyk

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Shantun Parmar · Accepted Answer · 2020-11-05 15:23:37Z

-2

You may try this

for VARIABLE in file1
do
    command1 on $VARIABLE
done

answered Nov 5, 2020 at 15:23

Shantun Parmar

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