Very Computer

by **Willia** » Thu, 02 Jun 2005 19:18:21

Hi all,

How can I use grep to find an exact pattern match, for example if I were to
grep the first field of the /etc/passwd file for "m",

awk -F: '{print $}' /etc/passwd | grep m

I get every userid that contains "m" in the passwd file, I'd like to
matching any occurrence of only "m" in this case?

--
Regards

William

by **laurentschnei..** » Thu, 02 Jun 2005 19:20:50

grep ^m: /etc/passwd

by **Willia** » Thu, 02 Jun 2005 19:25:50

> grep ^m: /etc/passwd

Thanks! what does the ^ and : symbols mean in the string?

--
Regards

William

by **Willia** » Thu, 02 Jun 2005 19:29:53

> > grep ^m: /etc/passwd

> Thanks! what does the ^ and : symbols mean in the string?

> --
> Regards

> William

If I try to match a numeric string using grep ^14: /etc/passwd this fails to
find anything, is there a different format for numeric strings?

--
Regards

William

by **Chris F.A. Johnso** » Thu, 02 Jun 2005 19:43:05

>> > grep ^m: /etc/passwd

>> Thanks! what does the ^ and : symbols mean in the string?

> If I try to match a numeric string using grep ^14: /etc/passwd this fails to
> find anything, is there a different format for numeric strings?

The caret (^) anchors the search to the beginning of the line. The
colon just matches a colon. Unless you have a user with the name
"14", that command will not find a match.

--
Chris F.A. Johnson <http://cfaj.freeshell.org>
==================================================================
Shell Scripting Recipes: A Problem-Solution Approach, 2005, Apress
<http://www.torfree.net/~chris/books/cfaj/ssr.html>

by **Willia** » Thu, 02 Jun 2005 19:51:09

> >> > grep ^m: /etc/passwd

> >> Thanks! what does the ^ and : symbols mean in the string?

> > If I try to match a numeric string using grep ^14: /etc/passwd this
fails to
> > find anything, is there a different format for numeric strings?

> The caret (^) anchors the search to the beginning of the line. The
> colon just matches a colon. Unless you have a user with the name
> "14", that command will not find a match.

> --
> Chris F.A. Johnson <http://cfaj.freeshell.org>
> ==================================================================
> Shell Scripting Recipes: A Problem-Solution Approach, 2005, Apress
> <http://www.torfree.net/~chris/books/cfaj/ssr.html>

Thanks Chris,

I'm also looking to find unique occurrences on group id's, for example if I
grep for GID 100, I find 1001, 1002 etc, however GID 100 is not there.. is
there a similar pattern match for numeric strings?

Regards

William

by **Loki Harfag** » Thu, 02 Jun 2005 20:07:37

Le Wed, 01 Jun 2005 10:51:09 +0000, William a crit?:

>> >> > grep ^m: /etc/passwd

>> >> Thanks! what does the ^ and : symbols mean in the string?

>> > If I try to match a numeric string using grep ^14: /etc/passwd this
> fails to
>> > find anything, is there a different format for numeric strings?

>> The caret (^) anchors the search to the beginning of the line. The
>> colon just matches a colon. Unless you have a user with the name
>> "14", that command will not find a match.

>> --
>> Chris F.A. Johnson <http://cfaj.freeshell.org>
>> ==================================================================
>> Shell Scripting Recipes: A Problem-Solution Approach, 2005, Apress
>> <http://www.torfree.net/~chris/books/cfaj/ssr.html>

> Thanks Chris,

> I'm also looking to find unique occurrences on group id's, for example if I
> grep for GID 100, I find 1001, 1002 etc, however GID 100 is not there..

Well, if no group has the value 100 it's not our fault !
Maybe you have no users #:D)
Try with :

$ grep :100: /etc/group
$ grep :100: /etc/passwd

if it works you made a typo in the grep you tried afore :-)

Quote:> is
> there a similar pattern match for numeric strings?

You're still quite confused (and confusing ;-) may I
suggest you to read som man pages and google a bit on regexp ?-D)

It is not to avoid answering to you but it should help you
having better questions ;-)

by **Chris F.A. Johnso** » Thu, 02 Jun 2005 20:10:29

>> >> > grep ^m: /etc/passwd

>> >> Thanks! what does the ^ and : symbols mean in the string?

>> > If I try to match a numeric string using grep ^14: /etc/passwd
>> > this fails to find anything, is there a different format for
>> > numeric strings?

>> The caret (^) anchors the search to the beginning of the line. The
>> colon just matches a colon. Unless you have a user with the name
>> "14", that command will not find a match.

> Thanks Chris,

> I'm also looking to find unique occurrences on group id's, for example if I
> grep for GID 100, I find 1001, 1002 etc, however GID 100 is not there.. is
> there a similar pattern match for numeric strings?

grep '^[^:]*:[^:]*:[^:]*:100:' /etc/passwd

"[^:]* == zero or more occurences of any character except ":"

Or you could use awk:

gid=100
awk -F: '$4 == gid {print}' gid=$gid /etc/passwd

({print} is not necessary, but I prefer to include it as it makes
the code clearer and future modifications easier.)

--
Chris F.A. Johnson <http://cfaj.freeshell.org>
==================================================================
Shell Scripting Recipes: A Problem-Solution Approach, 2005, Apress
<http://www.torfree.net/~chris/books/cfaj/ssr.html>

by **Willia** » Thu, 02 Jun 2005 20:12:00

> Le Wed, 01 Jun 2005 10:51:09 +0000, William a crit :

> >> >> > grep ^m: /etc/passwd

> >> >> Thanks! what does the ^ and : symbols mean in the string?

> >> > If I try to match a numeric string using grep ^14: /etc/passwd this
> > fails to
> >> > find anything, is there a different format for numeric strings?

> >> The caret (^) anchors the search to the beginning of the line. The
> >> colon just matches a colon. Unless you have a user with the name
> >> "14", that command will not find a match.

> >> --
> >> Chris F.A. Johnson <http://cfaj.freeshell.org>
> >> ==================================================================
> >> Shell Scripting Recipes: A Problem-Solution Approach, 2005, Apress
> >> <http://www.torfree.net/~chris/books/cfaj/ssr.html>

> > Thanks Chris,

> > I'm also looking to find unique occurrences on group id's, for example
if I
> > grep for GID 100, I find 1001, 1002 etc, however GID 100 is not there..

> Well, if no group has the value 100 it's not our fault !
> Maybe you have no users #:D)
> Try with :

> $ grep :100: /etc/group
> $ grep :100: /etc/passwd

> if it works you made a typo in the grep you tried afore :-)

> > is
> > there a similar pattern match for numeric strings?

> You're still quite confused (and confusing ;-) may I
> suggest you to read som man pages and google a bit on regexp ?-D)

> It is not to avoid answering to you but it should help you
> having better questions ;-)

I get it now :-)

I'll have some more daft questions later, don't worry :-)

Thanks

William

by **Sven Maschec** » Thu, 02 Jun 2005 20:31:20

> grep ^m: /etc/passwd

(Note that an unescaped ^ works like | in traditional Bourne shells.)

by **Willia** » Thu, 02 Jun 2005 21:24:31

> > grep ^m: /etc/passwd

> (Note that an unescaped ^ works like | in traditional Bourne shells.)

Thanks all for your help.

--
Regards

William

by **Ed Morto** » Thu, 02 Jun 2005 21:33:44

> Hi all,

> How can I use grep to find an exact pattern match, for example if I were to
> grep the first field of the /etc/passwd file for "m",

> awk -F: '{print $}' /etc/passwd | grep m

> I get every userid that contains "m" in the passwd file, I'd like to
> matching any occurrence of only "m" in this case?

Each line in the password file has this format:

account:password:UID:GID:GECOS:directory:shell

See http://www.rt.com/man/passwd.5.html for details.

So, there are 7 fields separated by ":"s. Here's examples of how to use
awk to find patterns in them by testing the specific fields $1 through $7:

To find an "account" that CONTAINS "m":

awk -F: '$1 ~ /m/' /etc/passwd

To find an "account" that STARTS WITH "m":

awk -F: '$1 ~ /^m/' /etc/passwd

To find an "account" that ENDS WITH "m":

awk -F: '$1 ~ /m$/' /etc/passwd

To find an "account" that IS EXACTLY "m", either:

awk -F: '$1 ~ /^m$/' /etc/passwd
awk -F: '$1 == "m"' /etc/passwd

To find a "GID" that IS EXACTLY "100", either:

awk -F: '$4 ~ /^100$/' /etc/passwd
awk -F: '$4 == "100"' /etc/passwd

And so on...

Hope that helps,

Ed.

by **Willia** » Thu, 02 Jun 2005 21:56:01

> > Hi all,

> > How can I use grep to find an exact pattern match, for example if I were
to
> > grep the first field of the /etc/passwd file for "m",

> > awk -F: '{print $}' /etc/passwd | grep m

> > I get every userid that contains "m" in the passwd file, I'd like to
> > matching any occurrence of only "m" in this case?

> Each line in the password file has this format:

> account:password:UID:GID:GECOS:directory:shell

> See http://www.rt.com/man/passwd.5.html for details.

> So, there are 7 fields separated by ":"s. Here's examples of how to use
> awk to find patterns in them by testing the specific fields $1 through $7:

> To find an "account" that CONTAINS "m":

> awk -F: '$1 ~ /m/' /etc/passwd

> To find an "account" that STARTS WITH "m":

> awk -F: '$1 ~ /^m/' /etc/passwd

> To find an "account" that ENDS WITH "m":

> awk -F: '$1 ~ /m$/' /etc/passwd

> To find an "account" that IS EXACTLY "m", either:

> awk -F: '$1 ~ /^m$/' /etc/passwd
> awk -F: '$1 == "m"' /etc/passwd

> To find a "GID" that IS EXACTLY "100", either:

> awk -F: '$4 ~ /^100$/' /etc/passwd
> awk -F: '$4 == "100"' /etc/passwd

> And so on...

> Hope that helps,

> Ed.

That does Ed, thanks!

Although I've written some scripts in the past, they've been nothing to
complicated and I should now learn more!

--
Regards

William

by **laurentschnei..** » Fri, 03 Jun 2005 22:15:39

Quote:> > grep ^m: /etc/passwd
> (Note that an unescaped ^ works like | in traditional Bourne shells.)

Thanks a lot for this correction, I did not know that one !

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