Bash using cut to separate an IP and Port

Question

I am trying to pass an ip and port to my bash script from a list of devices but the script is reading it as multiple devices instead of port. So in the example from below it's trying to telnet to 4 devices as it's reading the ports as a device.

for device in `cat device-list.txt`;
do
  hostname=$(echo $device | cut -d : -f 1)
  port=$(echo $port | cut -d : -f 2)
  ./script.exp $device $username $password $port ;
done

I am trying to use cut to take the port and pass it through as a variable so my telnet should be e.g. abc.abc.com 30040 as one device and so on.

 # Telnet
spawn telnet $hostname $port

This is my list of devices

abc.abc.com 30040
abc.abc.com 30041

I have tried searching this site already for answers.

score 4 · Answer 1 · answered May 23 '19 at 12:49

4

I see two errors (lines 4 & 5). It should be

 for device in `cat device-list.txt`;
 do
   hostname=$(echo $device | cut -d : -f 1)
   port=$(echo $device | cut -d : -f 2)
   ./script.exp $hostname $username $password $port ;
 done

answered May 23 '19 at 12:49

Ajay M

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Same output, still sees 4 IP's instead of 2 IP's and 2 ports – JelBoy May 23 '19 at 13:07
ah. I missed what your device-list.txt file looked like. Assumed that you had the `cut` command properly written. – Ajay M May 23 '19 at 14:58

pjh · Answer 2 · 2019-05-23T14:33:06.833

You can use the Bash built-in read function to extract hostname and port from the lines in a loop:

while read -r hostname port || [[ -n $hostname ]] ; do
    ./script.exp "$hostname" "$username" "$password" "$port"
done <device-list.txt

See Read a file line by line assigning the value to a variable for information about reading files line by line in Bash.
I've added quotes to stop Shellcheck warnings, and make the code safer.
See How to loop over the lines of a file? for an explanation of why the code in the question doesn't work.

score 0 · Answer 3 · answered May 23 '19 at 14:53

@pjh has the correct answer.

But here's some notes on your script:

you iterate over all the words of the file, rather than its lines.
using cut -d :, you specify the delimiter between fields as :. However, in your file you don't use : as the delimiter, but space ()
you calculate the $hostname variable by parsing $device, but then you use $device when calling the script
you calculate the $port variable by parsing the $port variable, which doesn't make any sense.

Here's an example on how to parse each line with cut:

cat device-list.txt | while read device; do
  hostname=$(echo $device | cut -d" " -f 1)
  port=$(echo $device | cut -d" " -f 2)
  ./script.exp $hostname $username $password $port
done

Bash using cut to separate an IP and Port

3 Answers3