bash - tshark command not recognized when launched from script file

Question

I am trying to write a simple bash file able to capture Wi-Fi traffic that looks like this:

STRING1="tshark -i 2 -a duration:5 -w <path of output.pcap>"
$STRING1
echo "'Wi-Fi' captured"

STRING2="tshark -r <path of output.pcap> -T fields -e frame.number -E header=y > <path of output.csv>"
echo $STRING2
$STRING2

The first command STRING1 is correctly processed and output.pcap is created. When STRING2 is launched i get the error tshark: Syntax error.. But if I just copy and paste the STRING2 command in the terminal everything works fine. What am I missing here?

Is it possible that your paths have spaces in them?

John Zwinck
– John Zwinck

2013-03-04 11:21:18 +00:00
Commented Mar 4, 2013 at 11:21 — John Zwinck
– John Zwinck, Commented Mar 4, 2013 at 11:21

chepner · Accepted Answer · 2013-03-04 13:49:37Z

1

Shell syntax (redirection operators, pipes, etc) are parsed before word expansion, so your output redirection is being passed as arguments to tshark.

STRING2="tshark -r <path of output.pcap> -T fields -e frame.number -E header=y"
echo $STRING2
$STRING2 > <path of output.csv>

answered Mar 4, 2013 at 13:49

chepner

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1 Comment

whiplash Over a year ago

Definitely a new-by in bash, am I? Thank you chepner!

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