get the first 5 characters from each line in shell script

If you want to use cut this way, you need to use redirection <<< (a here string) like:

var=$(cut -c-5 <<< "$line")

Note the use of var=$(command) expression instead of id= cut -c-5 $line. This is the way to save the command into a variable.

Also, use /bin/bash instead of /bin/sh to have it working.

---

Full code that is working to me:

#!/bin/bash

filename='sample.txt'
while read -r line
do
  id=$(cut -c-5 <<< "$line")
  echo $id
  #code for passing id to other script file as parameter
done < "$filename"

Well, its a one-liner cut -c-5 sample.txt. Example:

$ cut -c-5 sample.txt 
31113
31114
31111
31112

From there-on, you can pipe it to any other script or command:

$ cut -c-5 sample.txt | while read line; do echo Hello $line; done
Hello 31113
Hello 31114
Hello 31111
Hello 31112