awk

awk is a filter and output writer. When fed lots of text it can do some amazing things.

Here is a fairly gentle introduction to awk and it's uses. A trick to keep in mind is the field separator flag -F. Set this to adapt to something other than the default space delimited fields.

awk -F ":" '{print $1, $3, $4}' < /etc/passwd

will print the username, UID and GID for all users.

Print the username and default shell for each user
Print the sum of all the UID values and the sum of all the GID values for all users in /etc/passwd except the nfsnobody user.

awk answers

AWK

Print the username and default shell for each user

awk -F ":" '{print $1, $7}' </etc/passwd
root /bin/bash
jimroot /bin/bash
bin /sbin/nologin
daemon /sbin/nologin
adm /sbin/nologin
lp /sbin/nologin
sync /bin/sync
shutdown /sbin/shutdown

sabayon /sbin/nologin
gdm /sbin/nologin
tomcat /bin/sh
jim /bin/bash
jimtest /bin/bash

Print the sum of all the UID values and the sum of all the GID values for all users in /etc/passwd except the nfsnobody user.
```
awk -F ":" '{if ($3 < 10000) sumuid+=$3
    if ($4 < 10000) sumgid+=$4
    print "The sum of UID is " sumuid, " and the sum of GID is " sumgid}' < /etc/passwd | tail -n 1

The sum of UID is 20233  and the sum of GID is 14297
```
Since nfsnobody has a UID and GID that is far larger than 10,000, simply excluding it with a conditional "if" is easy.
The last part tail -n 1 will only print the last (-n 1) line. It has a counter part called head that works on the top of files.

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Linux Training : 6. awk

awk

awk answers