Useful One Line Programs

Many useful awk programs are short, just a line or two. Here is a collection of useful, short programs to get you started. Some of these programs contain constructs that haven't been covered yet. The description of the program will give you a good idea of what is going on, but please read the rest of the book to become an awk expert!

Most of the examples use a data file named `data'. This is just a placeholder; if you were to use these programs yourself, you would substitute your own file names for `data'.

awk '{ if (length($0) > max) max = length($0) }

END { print max }' data

This program prints the length of the longest input line.

awk 'length($0) > 80' data

This program prints every line that is longer than 80 characters. The sole rule has a relational expression as its pattern, and has no action (so the default action, printing the record, is used).

expand data | awk '{ if (x < length()) x = length() }

END { print "maximum line length is " x }'

This program prints the length of the longest line in `data'. The input is processed by the expand program to change tabs into spaces, so the widths compared are actually the right-margin columns.

awk 'NF > 0' data

This program prints every line that has at least one field. This is an easy way to delete blank lines from a file (or rather, to create a new file similar to the old file but from which the blank lines have been deleted).

awk 'BEGIN { for (i = 1; i <= 7; i++)

print int(101 * rand()) }'

This program prints seven random numbers from zero to 100, inclusive.

ls -lg files | awk '{ x += $5 } ; END { print "total bytes: " x }'

This program prints the total number of bytes used by files.

ls -lg files | awk '{ x += $5 }

END { print "total K-bytes: " (x + 1023)/1024 }'

This program prints the total number of kilobytes used by files.

awk -F: '{ print $1 }' /etc/passwd | sort

This program prints a sorted list of the login names of all users.

awk 'END { print NR }' data

This program counts lines in a file.

awk 'NR % 2' data

This program prints the even numbered lines in the data file. If you were to use the expression `NR % 2 == 1' instead, it would print the odd number lines.