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Full Discussion: Updating the comments field on /etc/passwd
Top Forums Shell Programming and Scripting Updating the comments field on /etc/passwd Post 302275842 by otheus on Monday 12th of January 2009 10:01:13 AM
Old 01-12-2009
First, overall, the script will probably work. Good job.

Second, using the usermod command is cool, and does a lot of the work for you. Make sure you manually back up the /etc/passwd file to a unique file. Otherwise every time you run the script (ie, fix a bug), the original backup will be removed. Just add "$$" to the backup file, and that will probably do the job.

Third, it's not necessary to cat | awk , nor to cat | grep | awk. If that helps you understand it better, fine. In both cases, awk will work on the file you give it. Awk will also act like grep. So you could do:
Code:
FIELD1=`awk -F: '$2 == "'"${i}"'" { print $3;exit; }' $FILE1`

Note, there are single quotes followed by double-quotes and vice versa. These make sure that the shell "sees" the variable you want it to see, but not the ones you want awk to see.

Searching by field makes sure that "SINLO" does not match both "SINLO" and "SINLO_R" and "ASINLO", for instance.

Similarly, I would change the "grep $FILE2" to:
Code:
awk -F: '$1 == "'"${i}"'" { found=1;exit; } END { exit(!found);}' $FILE2

This does the same thing as your grep command, but matches by field and exits with "true" as soon as a match is found. Otherwise, it exits with "false".

Third, you don't need to get FIELD1 until you know there's a matching entry in the passwd file. So put that line in the if-then condition.

Finally, to make sure your username matches the current server, you change the awk in the for loop to:
Code:
for i in `awk -F: '$1 == "'"$HOSTNAME"'" && $2 == '"${i}"' { print $2 }' $FILE1`

Again, double- and single-quoting needed like this.

Putting it all together we have:
Code:
#!/usr/bin/bash
FILE1=/tmp/update.txt
FILE2=/etc/passwd
cp $FILE2 /etc/passwd.$$.orig
TEST=echo

for i in `awk -F: '$1 == "'"$HOSTNAME"'" { print $2 }' $FILE1`
do
 if awk -F: '$1 == "'"${i}"'" { found=1; exit; } END { exit(!found);}' $FILE2
 then
   FIELD1=`awk -F: '$1 == "'"$HOSTNAME"'" && $2 == "'"${i}"'" { print $3;exit; }' $FILE1`
  $TEST usermod -c "${FIELD1}" $i
 fi
done

When the output shows the correct usermod commands, you are ready to go. Just change "TEST=echo" to "TEST=".
Last edited by otheus; 01-16-2009 at 04:21 AM.. Reason: Latest fix: loop variable should be i, not f
 

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LEARN ABOUT OSX

group

GROUP(5)						      BSD File Formats Manual							  GROUP(5)

NAME

     group -- format of the group permissions file

DESCRIPTION

     The file </etc/group> consists of newline separated ASCII records, one per group, containing four colon ':' separated fields. These fields
     are as follows:
	   group     Name of the group.
	   passwd    Group's encrypted password.
	   gid	     The group's decimal ID.
	   member    Group members.

     The group field is the group name used for granting file access to users who are members of the group.  The gid field is the number associ-
     ated with the group name.	They should both be unique across the system (and often across a group of systems) since they control file access.
     The passwd field is an optional encrypted password.  This field is rarely used and an asterisk is normally placed in it rather than leaving
     it blank.	The member field contains the names of users granted the privileges of group.  The member names are separated by commas without
     spaces or newlines.  A user is automatically in a group if that group was specified in their /etc/passwd entry and does not need to be added
     to that group in the /etc/group file.

INTERACTION WITH DIRECTORY SERVICES

     Processes generally find group records using one of the getgrent(3) family of functions.  On Mac OS X, these functions interact with the
     DirectoryService(8) daemon, which reads the /etc/group file as well as searching other directory information services to determine groups and
     group membership.

FILES

     /etc/group

SEE ALSO

     passwd(1), setgroups(2), crypt(3), getgrent(3), initgroups(3), passwd(5), DirectoryService(8)

BUGS

     The passwd(1) command does not change the group passwords.

HISTORY

     A group file format appeared in Version 6 AT&T UNIX.

Mac OS X							   July 18, 1995							  Mac OS X
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