In bash, how do I pass the while loops input to the cut command?

Question

How do I pass the $line to the cut command properly in this loop?

while read line
do
    login= $(cut -d : -f 1)

done < /etc/passwd

I can't do $(cut -d : -f 1 $line) so what is the correct way?

Answer 1

Let the read command together with the shell IFS variable parse the line for you:

while IFS=: read -r login restOfLine; do
    doSomethingWith $login
done < /etc/passwd

To answer your question, the bash here-string would be useful:

login=$(cut -d: -f1 <<< "$line")

Answer 2

Use echo:

login=$(echo "$line" | cut -d : -f 1)

Answer 3

You don't actually need the while loop if your intention is only to list the names. Also there is a syntax error after login=, there should be no space.

cut -d: -f1 /etc/passwd | \
while read login; 
do 
    echo username: $login;
done

or as you tried:

while read line; do
   login=$(echo $line | cut -d : -f 1)
   echo $login
done < /etc/passwd

even better:

db-getent passwd |cut -d: -f1 | xargs -L1 echo name: