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Full Discussion: sed or awk editing help
Top Forums Shell Programming and Scripting sed or awk editing help Post 302467851 by Scrutinizer on Sunday 31st of October 2010 07:13:32 PM
Old 10-31-2010
It was not a matter of which method is faster, but of which method actually works. Have a look at the 4th field that contains spaces and the letters sd, and what comes after that in post #17. That field should remain unchanged, but it is not, so IMO your original "non-loop" suggestion is not working properly. This needs to be done by either running the sed twice or through a loop like I suggested.

This time you are leaving your single step approach and you are presenting yet another alternative, with two search and replace statements (which you said earlier would not be necessary), which is like a loop with the use of the g flag.

One thing I noticed just now is that in post#11 in there was a g flag used but in the middle the sed -r option the g flag was accidentally missing. It is a little bit more efficient to leave that in as I noted in that same post. When we add the g-flag as was intended:
Code:
sed -r ':a;s/(,|^)  *(,|$)/\1\2/g;ta'

There is no significant difference on my system.

---------- Post updated 01-11-10 at 00:13 ---------- Previous update was 31-10-10 at 23:00 ----------

I tested you suggestion but it does not work properly for the last field:
Code:
$ echo '     ,          abc,             ,  sd   ,      ,   ,     ,      ' | sed -r ':a;s/(,|^)  *(,|$)/\1\2/g;ta' | od -c
0000000   ,                                           a   b   c   ,   ,
0000020           s   d               ,   ,   ,   ,  \n
0000034

cuts the spaces in the last field like it should, whereas
Code:
$ echo '     ,          abc,             ,  sd   ,      ,   ,     ,      ' | sed -r 's/(  *,|,|^)  *(,|$)/\1\2/g;s/,  *,/,,/g' | od -c
0000000   ,                                           a   b   c   ,   ,
0000020           s   d               ,   ,   ,   ,
0000040      \n
0000042

leaves them in.
Last edited by Scrutinizer; 10-31-2010 at 07:56 PM..
 

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LEARN ABOUT DEBIAN

shtool-subst

SHTOOL-SUBST.TMP(1)					      GNU Portable Shell Tool					       SHTOOL-SUBST.TMP(1)

NAME

       shtool-subst - GNU shtool sed(1) substitution operations

SYNOPSIS

       shtool subst [-v|--verbose] [-t|--trace] [-n|--nop] [-w|--warning] [-q|--quiet] [-s|--stealth] [-i|--interactive] [-b|--backup ext]
       [-e|--exec cmd] [-f|--file cmd-file] [file] [file ...]

DESCRIPTION

       This command applies one or more sed(1) substitution operations to stdin or any number of files.

OPTIONS

       The following command line options are available.

       -v, --verbose
	   Display some processing information.

       -t, --trace
	   Enable the output of the essential shell commands which are executed.

       -n, --nop
	   No operation mode. Actual execution of the essential shell commands which would be executed is suppressed.

       -w, --warning
	   Show warning on substitution operation resulting in no content change on every file. The default is to show a warning on substitution
	   operations resulted in no content change on all files.

       -q, --quiet
	   Suppress warning on substitution operation resulting in no content change.

       -s, --stealth
	   Stealth operation. Preserve timestamp on file.

       -i, --interactive
	   Enter interactive mode where the user has to approve each operation.

       -b, --backup ext
	   Preserve backup of original file using file name extension ext.  Default is to overwrite the original file.

       -e, --exec cmd
	   Specify sed(1) command directly.

       -f, --file cmd-file
	   Read sed(1) command from file.

EXAMPLE

	#   shell script
	shtool subst -i -e 's;(c) ([0-9]*)-2000;(c) 1-2001;' *.[ch]

	#    RPM spec-file
	%install
	    shtool subst -v -n 
		-e 's;^(prefix=).*;1 $RPM_BUILD_ROOT%{_prefix};g' 
		-e 's;^(sysconfdir=).*;1 $RPM_BUILD_ROOT%{_prefix}/etc;g' 
		`find . -name Makefile -print`
	    make install

HISTORY

       The GNU shtool subst command was originally written by Ralf S.  Engelschall <rse@engelschall.com> in 2001 for GNU shtool.  It was prompted
       by the need to have a uniform and convenient patching frontend to sed(1) operations in the OpenPKG package specifications.

SEE ALSO

       shtool(1), sed(1).

18-Jul-2008							   shtool 2.0.8 					       SHTOOL-SUBST.TMP(1)
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