How to use Internal Field Separator correctly?-CodePudding

I am trying to set the IFS to ':', but it seems to not work. Here is my code,

FILE="/etc/passwd"

while IFS=':' read -r line; do
        set $line
        echo $1
done < $FILE

When I run my code, it seems to give me the entire line. I have used the set command to assign positional parameters, to extract only the username, but it output the entire line when I try to print the first positional argument $1. What am I doing wrong?

CodePudding user response：

IFS=':' read -r line reads the complete line
IFS=':' read -r name remainder puts the first field in the variable name and the rest of the line in remainder
IFS=':' read -r name password remainder puts the first field in the variable name, the second field in the variable password and the rest of the line in remainder.
etc...

In bash you can use read -a array_var for getting an array containing all the fields, and that's probably the easiest solution for your purpose:

#!/bin/bash

while IFS=':' read -r -a fields
do
    echo "${fields[0]}"
done < /etc/passwd

CodePudding user response：

You're only setting IFS for the read command. When you expand the $line variable, it's set back to the original value. You need to set IFS there, not when reading.

oldIFS="$IFS" # save IFS
IFS=:

while read -r line; do
    set $line
    echo $1
done < $FILE

IFS="$oldIFS" # restore original IFS