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awk help

 
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# 1  
Old 12-06-2008
awk help
Hello everybody,

I'm studying for a UNIX exam. Can anyone explain this line please:

awk '{if(NF > 2) print $0 }' < /etc/passwd

It's the (NF > 2) part that I don't understand.

Thanks in advance!
# 2  
Old 12-06-2008
NF is a special variable meaning "number of fields". The logic reads, if the number of fields is greater then 2, print the line.

see the man page.
# 3  
Old 12-06-2008
This awk comand extract all the lines from /etc/passwd that have more than 2 fields in it.
By default the field separator will be the 'blank' .
For example :
This is my /etc/passwd file
cat /etc/passwd
root:x:0:0:root:/root:/bin/bash
bin:x:1:1:bin:/bin:/bin/sh
daemon:x:2:2:daemon:/sbin:/bin/sh
adm:x:3:4:adm:/var/adm:/bin/sh
lp:x:4:7:lp:/var/spool/lpd:/bin/sh
sync:x:5:0:sync:/sbin:/bin/sync
shutdown:x:6:0:shutdown:/sbin:/sbin/shutdown
halt:x:7:0:halt:/sbin:/sbin/halt
mail:x:8:12:mail:/var/spool/mail:/bin/sh
news:x:9:13:news:/var/spool/news:/bin/sh
uucp:x:10:14:uucp:/var/spool/uucp:/bin/sh
operator:x:11:0Smilieperator:/var:/bin/sh
games:x:12:100:games:/usr/games:/bin/sh
nobody:x:65534:65534:Nobody:/:/bin/sh
rpm:x:13:101:system user for rpm:/var/lib/rpm:/bin/false
messagebus:x:14:105:system user for dbus:/:/sbin/nologin
avahi:x:15:106:system user for avahi:/var/avahi:/bin/false
haldaemon:x:16:16:system user for hal:/:/sbin/nologin
vcsa:x:69:69:virtual console memory owner:/dev:/sbin/nologin
apache:x:70:70:system user for apache:/var/www:/bin/sh
postfix:x:71:71:system user for postfix:/var/spool/postfix:/bin/false
rpc:x:72:72:system user for portmap:/:/bin/false
gdm:x:73:73:system user for gdm:/var/lib/gdm:/bin/false
rpcuser:x:74:74:system user for nfs-utils:/var/lib/nfs:/bin/false
nscd:x:75:75:system user for glibc:/:/bin/false
sshd:x:76:76:system user for openssh:/var/empty:/bin/true
ftp:x:77:77:system user for proftpd:/var/ftp:/bin/false
arpwatch:x:78:78:system user for arpwatch:/var/lib/arpwatch:/bin/sh
mailnull:x:79:79:system user for sendmail:/var/spool/mqueue:/dev/null
smmsp:x:80:424:system user for sendmail:/var/spool/mqueue:/dev/null
clamav:x:81:425:system user for clamav:/var/lib/clamav:/bin/sh


and this is the output of the awk comand:

awk '{if(NF > 2) print $0 }' < /etc/passwd

rpm:x:13:101:system user for rpm:/var/lib/rpm:/bin/false
messagebus:x:14:105:system user for dbus:/:/sbin/nologin
avahi:x:15:106:system user for avahi:/var/avahi:/bin/false
haldaemon:x:16:16:system user for hal:/:/sbin/nologin
vcsa:x:69:69:virtual console memory owner:/dev:/sbin/nologin
apache:x:70:70:system user for apache:/var/www:/bin/sh
postfix:x:71:71:system user for postfix:/var/spool/postfix:/bin/false
rpc:x:72:72:system user for portmap:/:/bin/false
gdm:x:73:73:system user for gdm:/var/lib/gdm:/bin/false
rpcuser:x:74:74:system user for nfs-utils:/var/lib/nfs:/bin/false
nscd:x:75:75:system user for glibc:/:/bin/false
sshd:x:76:76:system user for openssh:/var/empty:/bin/true
ftp:x:77:77:system user for proftpd:/var/ftp:/bin/false
arpwatch:x:78:78:system user for arpwatch:/var/lib/arpwatch:/bin/sh
mailnull:x:79:79:system user for sendmail:/var/spool/mqueue:/dev/null
smmsp:x:80:424:system user for sendmail:/var/spool/mqueue:/dev/null
# 4  
Old 12-06-2008
Thanks a lot guys!
 
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