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Old 11-02-2011, 05:05 PM   #1
Registered: Jun 2003
Distribution: Gentoo baby, gentoo
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grep groups, gid, UID, etc -

Maybe I am going about this the wrong way. I need to be able to grab a users group ID's to set a model after account.

So if I do:

id userid

I get the following line -
uid=1001(userid) gid=2000(groupname1) groups=2000(groupname2),1000(groupname3),1500(groupname4)

How could I get just the groups ID's returned?

Obviously I start out with
id userid|

but pipe to what? Grep returns the whole line, so it looks like I need to use AWK or SED -

Could someone provide an example on how I could get the following output:

I need the group ID's only so I can place them in some variable to use on a user creation script. So basically get the model after's name, and then output each group as a seperate line...

Any idea on how, or even better, could someone provide an example? my brain hurts from the sed and awk tutorials and I just dont think I can get it with out a working example.

Thanks for any help you can provide.
Old 11-02-2011, 09:56 PM   #2
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The id command can be set to only output the groups, ie:
id -G userid
If you need separate lines, you can just use tr:
id -G userid | tr ' ' '\n'
You can use grep for simple pattern outputs, using the '-o' flag to restrict the output to the matches, as the following example shows (this makes assumptions such as group names not having embedded numbers, so isn't foolproof):
id userid | grep -o 'groups.*' | grep -o '[0-9]*'
If you are going to put time into learning a text oriented scripting language, consider learning perl instead of awk; it isn't as sleek as sed, but has a wider range of applications.

Last edited by neonsignal; 11-02-2011 at 10:12 PM.
Old 11-03-2011, 06:56 AM   #3
David the H.
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bash also sets a GROUPS array variable, holding the current user's group membership, if that's all you need.

echo "${GROUPS[@]}"
An array can also be used to hold and manipulate the output values of id, as opposed to working with tr or whatnot to change the delimiter. You can use the IFS setting to decide how the list is delimited when printed if you want (when using the ${array[*]} form).

ids=( $( id -G username ) )

IFS=$'\n'	#to delimit the list with newlines
echo "${ids[*]}"
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Old 11-03-2011, 03:25 PM   #4
Registered: Jun 2003
Distribution: Gentoo baby, gentoo
Posts: 148

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Wow neon - thanks a mil! that is exactly what I needed to get my output right.

David - your solution seems what I want going down the road, the right way.

I got my script done thanks to neon, but I would really like to work on Dave's solution and post up what my example should look like.

Off to hit the tutorials on bash arrays


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