Awk
awk
pattern {action}
pattern {action}
$ awk '{print $2}' /etc/fstab
to filter out comment lines - starting with #
$ awk '/^[^#]/ {print $2}' /etc/fstab
to grep on TWO occurences (AND operator)
$ awk '/pattern1/ && /pattern2/' /var/log/messages
case insensitive
$ awk '/pattern1/ && /pattern2/' IGNORECASE=1 /var/log/messages
print first field from password file using field seperator ':'
$ awk -F: '{print$1}' /etc/passwd
print only user ID > 500
$ awk -F: '$3>=500 {print$1}' /etc/passwd
display average of numbers entereed on a line:
$ awk '{ sum=0; for (i=1; i<=NF; i++) sum +=$i; print sum/NF; }'
| NF | number of fields in the current line |
| NR | the current record number (line number) |
| FS | input field seperator (space by default) |
| RS | record seperator (newline by default) |
| Example | Example |
| Example | Example |
| Example | Example |
| Example | Example |
| Example | Example |
show the 5th record on the second line:
df /tmp | awk 'NR==2 {print$5 }'
use awk with a program
the file maxuid:
BEGIN {maxuid = 0; FS=":" }
{ if ($3 > maxuid) maxuid = $3 }
END { print" the largest UID is ", maxuid }
then use awk like this:
$ awk -f maxuid /etc/passwd
to ignore user nobody:
BEGIN {maxuid = 0; FS=":" }
$1 != "nobody" { if ($3 > maxuid) maxuid = $3 }
END { print" the largest UID is ", maxuid }
cat -n: (adds line numbers)
$ awk '{ print NR, $0}' /etc/fstab
wc -w: (count words)
$ awk '{ w += NF } END { print w}' /etc/fstab
grep chris /etc/passwd:
$ awk '/^chris/' /etc/passwd
writing self contained scripts
#!/usr/bin/awk -f
{ cost[$1] += $2*$4 }
END { for (cat in cost) print cat, cost[cat] }
chmod u+x catscript ./catscript