Understanding sed Post: 302774763

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Top Forums Shell Programming and Scripting Understanding sed Post 302774763 by Scrutinizer on Sunday 3rd of March 2013 05:25:00 AM

03-03-2013

Moderator

@alister:
There seems to be no difference with a single (first) substitution or a global substitution, but only with the flag with a specific number. The difference is about a zero match after a previous match (was it already covered by a previous match or not?). Compare:

Code:

$ echo :BEFORE: | gsed 's/[^:]*/AFTER/'
AFTER:BEFORE:
$ echo :BEFORE: | sed 's/[^:]*/AFTER/'
AFTER:BEFORE:

$ echo :BEFORE: | gsed 's/[^:]*/AFTER/2'
:AFTER:
$ echo :BEFORE: | sed 's/[^:]*/AFTER/2'
:AFTER:

$ echo :BEFORE: | gsed 's/[^:]*/AFTER/3'
:BEFORE:AFTER
$ echo :BEFORE: | sed 's/[^:]*/AFTER/3'
:BEFOREAFTER:

$ echo :BEFORE: | gsed 's/[^:]*/AFTER/4'
:BEFORE:
$ echo :BEFORE: | sed 's/[^:]*/AFTER/4'
:BEFORE:AFTER

$ echo :BEFORE: | gsed 's/[^:]*/AFTER/5'
:BEFORE:
$ echo :BEFORE: | sed 's/[^:]*/AFTER/5'
:BEFORE:

$ echo :BEFORE: | gsed 's/[^:]*/AFTER/g'
AFTER:AFTER:AFTER
$ echo :BEFORE: | sed 's/[^:]*/AFTER/g'
AFTER:AFTER:AFTER

$ echo x:BEFORE: | gsed 's/[^:]*/AFTER/2'
x:AFTER:
$ echo x:BEFORE: | sed 's/[^:]*/AFTER/2'
xAFTER:BEFORE:

Last edited by Scrutinizer; 03-03-2013 at 02:02 PM..

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LEARN ABOUT SUNOS

echo

echo(1B)					     SunOS/BSD Compatibility Package Commands						  echo(1B)

NAME

       echo - echo arguments to standard output

SYNOPSIS

       /usr/ucb/echo [-n] [argument]

DESCRIPTION

       echo writes its arguments, separated by BLANKs and terminated by a NEWLINE, to the standard output.

       echo  is useful for producing diagnostics in command files and for sending known data into a pipe, and for displaying the contents of envi-
       ronment variables.

       For example, you can use echo to determine how many subdirectories below the root directory (/) is your current directory, as follows:

	 o  echo your current-working-directory's full pathname

	 o  pipe the output through tr to translate the path's embedded slash-characters into space-characters

	 o  pipe that output through wc -w for a count of the names in your path.

	      example% /usr/bin/echo "echo $PWD | tr '/' ' ' | wc -w"

       See tr(1) and wc(1) for their functionality.

       The shells csh(1), ksh(1), and sh(1), each have an echo built-in command, which, by default, will have precedence, and will be  invoked	if
       the  user  calls  echo without a full pathname. /usr/ucb/echo and csh's echo() have an -n option, but do not understand back-slashed escape
       characters. sh's echo(), ksh's echo(), and /usr/bin/echo, on the other hand, understand the  black-slashed  escape  characters,	and  ksh's
       echo() also understands a as the audible bell character; however, these commands do not have an -n option.

OPTIONS

       -n	Do not add the NEWLINE to the output.

ATTRIBUTES

       See attributes(5) for descriptions of the following attributes:

       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWscpu			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       csh(1), echo(1), ksh(1), sh(1), tr(1),  wc(1), attributes(5)

NOTES

       The -n option is a transition aid for BSD applications, and may not be supported in future  releases.

SunOS 5.10							    3 Aug 1994								  echo(1B)