bash scripting , loop not looping - loops

Question

I wrote a while loop to search inside files and append the output to a text file , but it seems like it's reading only the first line of that text file . How do I fix it ?
while read line
do
x=`echo $line`
y=`grep $x: /etc/group | cut -d ":" -f 3`
grep $y /etc/passwd | cut -d ":" -f 1 >> users
grep $y /etc/group | cut -d ":" -f 4 | tr "," "\n" >> users
done < filename

Answer 1

Perhaps you need to wrap $x and $y in quotes, as otherwise grep may interpret anything after the first space as the name of the file to be searched:
#!/bin/bash
while read line
do
x=`echo $line`
y=`grep "$x:" /etc/group | cut -d ":" -f 3`
grep "$y" /etc/passwd | cut -d ":" -f 1 >> users
grep "$y" /etc/group | cut -d ":" -f 4 | tr "," "\n" >> users
done < filename

Answer 2

This might be a bit safer as some of the grep statements may pick up the wrong fields (i.e. it does not check for the correct field):
while read GROUP
do
GROUP_ID=`grep ^$GROUP: /etc/group | cut -d ":" -f 3`
USER_ENT=`grep -e '\(.*:\)\{3\}'$GROUP_ID':' /etc/passwd`
[ $? -eq 0 ] && cut -d ":" -f 1 <<<$USER_ENT
GROUP_ENT=`grep -e '\(.*:\)\{2\}'$GROUP_ID':' /etc/group`
[ $? -eq 0 ] && cut -d ":" -f 4 <<<$GROUP_ENT | tr "," "\n" | grep -v ^$
done < $FILE_NAME | sort | uniq >users