Guillaume: 1 revision

2008-12-03T10:39:01Z

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192.168.20.177 at 09:23, 30 January 2008

2008-01-30T09:23:28Z

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A lot of nice things can be said about [[Perl one-liners|one-liners]] in [[Perl]], but one example should suffice to give an understanding of their power and beauty:

==One-liners==
The following line reads the STDIN, concatenates a line at the end and prints to STDOUT. Its useful to concatenate arguments in STDOUT before calling a command:
>dir /B | perl -we"print<>;print'du'"

The following line reads the filename.txt content as the standard input and outputs the substituted content:
perl -p -e "s/old text/new text/gi;" < filename.txt

The next line reads the filename.txt content and writes the substituted content
while keeping a backup of the original file (.bak):
perl -pi.bak -e "s/old text/new text/gi;" filename.txt

The next line reads an input file for a match. If match is found then splits the line by '/' char and prints the last element.
perl -F\/ -lane perl "if (m|MATCH|{$a=pop @F; print $a;})" < input.txt

The next lines reads input file and prints ok if a match is found:
perl -nwe"if(m/MATCH/gi){print'Ok';}" < input.txt

The next line reads stdinput, splits it, and prints it in uppercase:
> echo EV_prefix.tmp | perl -F[_\.] -wlane'pop@F;$a=pop@F;print uc($a);'
PREFIX

The next line extracts values from xml tags:
> curl http://www.cnn.com | perl -ne 'm/>([^<>]*?)<\// && print$1."\n"' | sed -e '/^$/d'

==Utilities==
===Rename ''htm'' to ''html'' files===
In windows:

>dir /B /S | perl -wlne"/([^ ]+)\.htm$/i&&rename$1.'.htm',$1.'.html'"

In linux:

>find | grep htm | perl -wlne'/([^ ]+)\.htm$/i&&rename$1.".htm",$1.".html"'

===Copy files matching MATCH to SUBST===
In windows:
>dir /B /S | perl -MFile::Copy -wlne"/(([^ ]+)MATCH([^ ]+))/&&copy$1,$2.'SUBST'.$3"
In linux:
>find | grep MATCH | perl -MFile::Copy -wlne'/(([^ ]+)MATCH([^ ]+))/&&copy$1,$2."SUBST".$3'

===Parsing MOHID code for keywords===
This little [[Perl one-liners|one-liner]] utility allows to parse MOHID code for keywords and default values:
> more ModuleGeometry.F90 | perl -wlne"m/keyword.+'(.+)'/gi && print $1; m/default.+=(.+),/gi && print $1;"

===Lookahead and lookbehind===
This little perl program illustrates the use of ''lookahead''(?=) and ''lookbehind''(?<=) (as shown in I'mMike):
$ perl -e '$num = 8927369280;'\
> '$num =~ s/(?<=\d)(?=(\d\d\d)+$)/,/g;'\
> 'print $num, "\n"'
8,927,369,280

==Troubleshoots==
Q:Why my perl one-liners work in windows and don't work in linux, or vice-versa?
A: Under windows you must encapsule the command in double-quotes (""),
whereas in linux you must encapsule commands in single-quotes (' ').

==See also==
*[[Perl]]
*[[Regexp]]
*[[Bash]]

[[Category:Linux]]
[[Category:Windows]]
[[Category:Perl]]
[[Category:Programming]]

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Guillaume: 1 revision

192.168.20.177 at 09:23, 30 January 2008