script question

[navin]

Hello ,
i have 2 files called users and /etc/passwd.
I need to grep the users from /etc/passwd .
I'm using the below script ,...what is wrong.please advice
for i in $users ; do
>grep $i /etc/passwd >/tmp/users1
>done

Thanks much

[Juan M Leon · Accepted solution]

Navin,

You need a small modification in your script

for i in `cat users` ; do
grep $i /etc/passwd >> /tmp/users1
done


"cat users " I assume that the file is users and it has one field per record with the UID

">>" You need to put double redirect. otherwise you will only have the last successful record in the users1 file.
>> means add at the end where > means clear and add in this file.

good luck

[Juan M Leon]

Note : Please dont forget to assign points.
Thank you

[Geoff Wild]

Or sans cat:

for i in $(grep $i /etc/passwd >/tmp/users1
done


Rgds...Geoff

[Sandman!]

To print all users that have an entry in the "users file" and a corresponding entry in the /etc/passwd file use the following:

# grep -f /etc/passwd

[Juan M Leon]

Sandman,

I like your oneline script.
very simple... =)

[Patrick Wallek]

The problem with the ways mentioned is that they will look for ALL occurrences of whatever is in the users file.

Say you have a file like:

tom
dick
harry

When you grep as the folks have done above you could get the users:

tom
tomsmit
dick
dickjr
harry
harry2

It would also be possible to gets matches in other areas of each line, like the home directory or GECOS field.

If you want to look for specific user names only you could do:

for i in $( grep ^${i}: /etc/passwd >/tmp/users1
done

The '^${i}:' will look for ${i} ONLY at the beginning of each line with a ':' after it. So it would show only:

tom:*:UID:GID:GECOS:homedir:shell
dick:*:UID:GID:GECOS:homedir:shell
harry:*:UID:GID:GECOS:homedir:shell