Editing One-liner program (section)

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

===BASIC===
[[File:10print.gif|thumb|Simulated output of the ''10PRINT'' one-liner BASIC program for the Commodore 64]]
A single line of BASIC can typically hold up to 255 characters, and one liners ranged from simple games<ref>{{cite web |title=Acorn User One-Line Games (Escape From Voros, Lexxias, Race To Varpon, Storm Clouds Over Zaqqit, Zander (AKA Lurch)) |url=http://bbcmicro.co.uk/game.php?id=2718 |website=bbcmicro.co.uk |accessdate=3 July 2018 |language=en}}</ref> to graphical demos. One of the better-known demo one-liners is colloquially known as ''10PRINT'', written for the [[Commodore 64]]:
<syntaxhighlight lang="cbmbas">
10 PRINT CHR$(205.5+RND(1)); : GOTO 10
</syntaxhighlight>

===C===
The following example is a [[C (programming language)|C]] program (a winning entry in the "Best one-liner" category of the [[IOCCC]]).
<syntaxhighlight lang="C">
main(int c,char**v){return!m(v[1],v[2]);}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);}
</syntaxhighlight>

This one-liner program is a glob pattern matcher. It understands the glob characters {{code|*}}, meaning zero or more characters, and {{code|?}}, meaning exactly one character, just like most [[Unix shell]]s.

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:
<syntaxhighlight lang="console">
$ ./a.out foo 'f??'; echo $?
$ ./a.out 'best short program' '??st*o**p?*'; echo $?
</syntaxhighlight>

===AWK===
The book ''[[The AWK Programming Language]]'' contains 20 examples of ''one-liners'' at the end of the book's first chapter.

Here are the very first of them:
# Print the total number of input lines (like [[wc (Unix)|wc -l]]): <syntaxhighlight lang="awk">END { print NR }</syntaxhighlight>
# Print the tenth input line: <syntaxhighlight lang="awk">NR == 10</syntaxhighlight>
# Print the last field of every input line: <syntaxhighlight lang="awk">{ print $NF }</syntaxhighlight>

===J===
Here are examples in [[J (programming language)|J]]:
* A function avg to return the average of a list of numbers: <syntaxhighlight lang="j">avg=: +/ % #</syntaxhighlight>
* [[Quicksort]]: <syntaxhighlight lang="j">quicksort=: (($:@(<#[) , (=#[) , $:@(>#[)) ({~ ?@#)) ^: (1<#)</syntaxhighlight>

===Perl===
Here are examples in the [[Perl]] [[programming language]]:
* Look for duplicate words
 perl -0777 -ne '<syntaxhighlight lang="perl" inline>print "$.: doubled $_\n" while /\b(\w+)\b\s+\b\1\b/gi</syntaxhighlight>' 
* Find Palindromes in /usr/dict/words
 perl -lne '<syntaxhighlight lang="perl" inline>print if $_ eq reverse</syntaxhighlight>' /usr/dict/words
* in-place edit of *.c files changing all foo to bar
 perl -p -i.bak -e '<syntaxhighlight lang="perl" inline>s/\bfoo\b/bar/g</syntaxhighlight>' *.c

Many one-liners are practical. For example, the following [[Perl]] one-liner will reverse all the bytes in a file:
<syntaxhighlight lang="bash">
perl -0777e 'print scalar reverse <>' filename
</syntaxhighlight>

While most [[Perl]] one-liners are imperative, Perl's support for anonymous functions, closures, map, filter ([[grep]]) and fold (List::Util::reduce) allows the creation of 'functional' one-liners.

This one-liner creates a function that can be used to return a list of primes up to the value of the first parameter:
<syntaxhighlight lang="perl">
my $z = sub { grep { $a=$_; !grep { !($a % $_) } (2..$_-1)} (2..$_[0]) }
</syntaxhighlight>
It can be used on the command line, like this:

 perl -e'<syntaxhighlight lang="bash" inline>$,=",";print sub { grep { $a=$_; !grep { !($a % $_) } (2..$_-1)} (2..$_[0]) }->(shift)</syntaxhighlight>' number

to print out a comma-separated list of primes in the range 2 - number.

===Haskell===
The following [[Haskell (programming language)|Haskell]] program is a one-liner: it sorts its input lines [[ASCII#Order|ASCIIbetically]].
<syntaxhighlight lang="haskell">
main = (mapM_ putStrLn . Data.List.sort . lines) =<< getContents -- In ghci a qualified name like Data.List.sort will work, although as a standalone executable you'd need to import Data.List.
</syntaxhighlight>

An even shorter version:
<syntaxhighlight lang="haskell">
main = interact (unlines . Data.List.sort . lines) -- Ditto.
</syntaxhighlight>

Usable on the command line like:
<syntaxhighlight lang="bash">
cat filename | ghc -e "interact (unlines . Data.List.sort . lines)"
</syntaxhighlight>

===Racket===
The following [[Racket (programming language)|Racket]] program is equivalent to the above Haskell example:
<syntaxhighlight lang="racket">
#lang racket
(for-each displayln (sort (port->lines) string<?))
</syntaxhighlight>
and this can be used on the command line as follows:
 racket -e '<syntaxhighlight lang="racket" inline>(for-each displayln (sort (port->lines) string<?))</syntaxhighlight>'

===Python===
Performing one-liners directly on the Unix command line can be accomplished by using [[Python (programming language)|Python]]'s -cmd flag (-c for short), and typically requires the import of one or more modules. Statements are separated using ";" instead of newlines. For example, to print the last field of unix long listing:
 ls -l | python -c "<syntaxhighlight lang="python" inline>
import sys;[sys.stdout.write(' '.join([line.split(' ')[-1]])) for line in sys.stdin]</syntaxhighlight>"

====Python wrappers====
Several open-source scripts have been developed to facilitate the construction of Python one-liners. Scripts such as 
[http://code.google.com/p/pyp/ pyp] or [http://code.activestate.com/recipes/437932-pyline-a-grep-like-sed-like-command-line-tool/ Pyline] import commonly used modules and provide more human-readable variables in an attempt to make Python functionality more accessible on the command line. Here is a redo of the above example (printing the last field of a unix long listing):
<syntaxhighlight lang="bash">
ls -l | pyp "whitespace[-1]" # "whitespace" represents each line split on white space in pyp
ls -l | pyline "words[-1]"  # "words" represents each line split on white space in pyline
</syntaxhighlight>

====Executable libraries====
The Python CGIHTTPServer module for example is also an executable library that performs as a web server with CGI. To start the web server enter:
<syntaxhighlight lang="console">$ python -m CGIHTTPServer
Serving HTTP on 0.0.0.0 port 8000 …</syntaxhighlight>

===Tcl===
[[Tcl]] (Tool Command Language) is a dynamic programming/scripting language based on concepts of Lisp, C, and Unix shells. It can be used interactively, or by running scripts (programs) which can use a package system for structuring.<ref>Following are direct quotes from {{Wikibooks-inline|Tcl Programming}} that are available under the [[Creative Commons Attribution-ShareAlike License]].</ref>

Many strings are also well-formed lists. Every simple word is a list of length one, and elements of longer lists are separated by whitespace. For instance, a string that corresponds to a list of three elements:
<syntaxhighlight lang="TCL">
set example {foo bar grill}
</syntaxhighlight>

Strings with unbalanced quotes or braces, or non-space characters directly following closing braces, cannot be parsed as lists directly. You can explicitly split them to make a list.

The "constructor" for lists is of course called list. It's recommended to use when elements come from variable or [[command substitution]] (braces won't do that). As Tcl commands are lists anyway, the following is a full substitute for the list command:
<syntaxhighlight lang="TCL">
proc list args {set args}
</syntaxhighlight>

===Windows PowerShell===
Finding palindromes in file words.txt
<syntaxhighlight lang="powershell">
Get-Content words.txt | Where { $_ -eq -join $_[($_.length-1)..0] }
</syntaxhighlight>

Piping semantics in PowerShell help enable complex scenarios with one-liner programs. This one-liner in PowerShell script takes a list of names and counts from a comma-separated value file, and returns the sum of the counts for each name.
<syntaxhighlight lang="powershell">
ipcsv .\fruit.txt –H F, C|Group F|%{@{"$($_.Name)"=($_.Group|measure C -sum).Sum}}|sort value
</syntaxhighlight>