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Full Discussion: Scratching my head over old post
Top Forums Shell Programming and Scripting Scratching my head over old post Post 303003144 by apmcd47 on Friday 8th of September 2017 04:16:56 AM
Old 09-08-2017
Quote:
Originally Posted by OMLEELA
Hello !

Pondering over some old post & I need some help.

Questions -
1. In there , the magic is happening all because of $0=$2. Can someone please explain to me as to what does $0=$2 means ?
2. Also can someone go over the sed operation here as I tried to understand this for the past 2 hours and I am not getting anywhere with this.


best regards,
Lee.
In awk $0 refers to the whole record (line) while $1, $2 ... refer to the individual fields. So $0=$2 simply replaces the whole record with field 2.

In sed the (escaped) parentheses earmark part of a pattern for a later reference.

Take for instance this:
Code:
$ echo "charlie farley" | sed 's/\(charlie\) .*/\1 chaplin/'
charlie chaplin
$ echo "piggy malone" | sed 's/\(charlie\) .*/\1 chaplin/'
piggy malone

So basically I want to change "charlie farley" into "charlie chaplin" (or any other charlie) but leave anything else alone. I this extremely simple example I could have written
Code:
$ echo "charlie farley" | sed 's/charlie .*/charlie chaplin/'

But consider this
Code:
$ echo "charlie farley" | sed 's/\(charl.*\) .*/\1 chaplin/'

Now I can catch "charles" or "charley" too. More general.

The \1 refers to the first earmarked pattern. But what if I do two of them?
Code:
$ echo "Charles Chaplin" | sed 's/\(.*\) \(.*\)/\2, \1/'
Chaplin, Charles

This last example takes two strings separated by a space and reverses them, putting a comma between.

Hope that helps.

Andrew
 

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LEARN ABOUT MOJAVE

locale::codes::langext5.18

Locale::Codes::LangExt(3pm)				 Perl Programmers Reference Guide			       Locale::Codes::LangExt(3pm)

NAME

       Locale::Codes::LangExt - standard codes for language extension identification

SYNOPSIS

	  use Locale::Codes::LangExt;

	  $lext = code2langext('acm');		       # $lext gets 'Mesopotamian Arabic'
	  $code = langext2code('Mesopotamian Arabic'); # $code gets 'acm'

	  @codes   = all_langext_codes();
	  @names   = all_langext_names();

DESCRIPTION

       The "Locale::Codes::LangExt" module provides access to standard codes used for identifying language extensions, such as those as defined in
       the IANA language registry.

       Most of the routines take an optional additional argument which specifies the code set to use. If not specified, the default IANA language
       registry codes will be used.

SUPPORTED CODE SETS

       There are several different code sets you can use for identifying language extensions. A code set may be specified using either a name, or
       a constant that is automatically exported by this module.

       For example, the two are equivalent:

	  $lext = code2langext('acm','alpha');
	  $lext = code2langext('acm',LOCALE_LANGEXT_ALPHA);

       The codesets currently supported are:

       alpha
	   This is the set of three-letter (lowercase) codes from the IANA language registry, such as 'acm' for Mesopotamian Arabic.

	   This is the default code set.

ROUTINES

       code2langext ( CODE [,CODESET] )
       langext2code ( NAME [,CODESET] )
       langext_code2code ( CODE ,CODESET ,CODESET2 )
       all_langext_codes ( [CODESET] )
       all_langext_names ( [CODESET] )
       Locale::Codes::LangExt::rename_langext  ( CODE ,NEW_NAME [,CODESET] )
       Locale::Codes::LangExt::add_langext  ( CODE ,NAME [,CODESET] )
       Locale::Codes::LangExt::delete_langext  ( CODE [,CODESET] )
       Locale::Codes::LangExt::add_langext_alias  ( NAME ,NEW_NAME )
       Locale::Codes::LangExt::delete_langext_alias  ( NAME )
       Locale::Codes::LangExt::rename_langext_code  ( CODE ,NEW_CODE [,CODESET] )
       Locale::Codes::LangExt::add_langext_code_alias  ( CODE ,NEW_CODE [,CODESET] )
       Locale::Codes::LangExt::delete_langext_code_alias  ( CODE [,CODESET] )
	   These routines are all documented in the Locale::Codes::API man page.

SEE ALSO

       Locale::Codes
	   The Locale-Codes distribution.

       Locale::Codes::API
	   The list of functions supported by this module.

       http://www.iana.org/assignments/language-subtag-registry
	   The IANA language subtag registry.

AUTHOR

       See Locale::Codes for full author history.

       Currently maintained by Sullivan Beck (sbeck@cpan.org).

COPYRIGHT

	  Copyright (c) 2011-2013 Sullivan Beck

       This module is free software; you can redistribute it and/or modify it under the same terms as Perl itself.

perl v5.18.2							    2013-11-04					       Locale::Codes::LangExt(3pm)
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