One-liner Program - Examples

Examples

The TAPL book contains 20 examples of One-liners (A Handful of Useful awk One-Liners) at the end of the book's first chapter.

Here are the very first of them:

1. Print the total number of input lines: END { print NR }
2. Print the tenth input line: NR == 10
3. Print the last field of every input line: { print $NF }

Here are examples in J:

1. A function avg to return the average of a list of numbers: avg=: +/ % #
2. Quicksort: quicksort=: (($:@(<#[), (=#[), $:@(>#[)) ({~ ?@#)) ^: (1<#)

Here are examples in Perl:

• Look for duplicate words perl -0777 -ne 'print "$.: doubled $_\n" while /\b(\w+)\b\s+\b\1\b/gi'
• Find Palindromes in /usr/dict/words perl -lne 'print if $_ eq reverse' /usr/dict/words
• in-place edit of *.c files changing all foo to bar perl -p -i.bak -e 's/\bfoo\b/bar/g' *.c

Many one-liners are practical. For example, the following Perl one-liner will reverse all the bytes in a file:

perl -0777e 'print scalar reverse <>' filename

One-liners are also used to show off the differential expressive power of programming languages. Frequently, one-liners are used to demonstrate programming ability. Contests are often held to see who can create the most exceptional one-liner.

The following example is a C program (a winning entry in the "Best one-liner" category of the IOCCC, here split to two lines for presentation).

main(int c,char**v){return!m(v,v);}m(char*s,char*t){return *t-42?*s?63==*t|*s==*t&&m(s+1,t+1):!*t:m(s,t+1)||*s&&m(s+1,t);}

This one-liner program is a glob pattern matcher. It understands the glob characters `*' meaning `zero or more characters' and `?' meaning exactly one character, just like most Unix shells.

Run it with two args, the string and the glob pattern. The exit status is 0 (shell true) when the pattern matches, 1 otherwise. The glob pattern must match the whole string, so you may want to use * at the beginning and end of the pattern if you are looking for something in the middle. Examples:

$ prog foo 'f??'; echo $? $ prog 'best short program' '??st*o**p?*'; echo $?