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Full Discussion: sed pattern matching question
Top Forums Shell Programming and Scripting sed pattern matching question Post 302518171 by mirni on Thursday 28th of April 2011 07:33:55 PM
Old 04-28-2011
Quote:
From what I can tell the whole string (ABCD|/p) is a literal.
Mmmmm... no.
The string 'ABCD|' is a literal, the rest '/p' is the end of regex ('/') and print command ('p'). So the first sed command
Code:
sed -n -e '/^.*ABCD|/p'

is an instruction to print only lines containing 'ABCD|'. There is some redundancy there; the following would do the same:
Code:
sed -n -e '/ABCD|/p'

The second sed removes the beginning of line until ABCD| including. Note that matching here is greedy, so if you have multiple instances of ABCD| there, the pattern is gonna match the longest possible substring. E.g.:
Code:
$ echo "blah|ABCD|hhhh|fals.;and&+324ABCD|ooo|ABCD" | sed -e 's/^.*ABCD|//' 
ooo|ABCD

The third one removes trailing '|ABCD'

We could simplify this as :
Code:
sed -n '/ABCD|/{  #do the following on lines containing "ABCD|"
            s/^.*ABCD|// ;  #eat the longest substring from beginning to "ABCD|"
            s/|ABCD$//;     # eat the  last "|ABCD" just before end of line
            p }'               # and print it

Last edited by mirni; 04-28-2011 at 08:40 PM..
This User Gave Thanks to mirni For This Post:
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LEARN ABOUT LINUX

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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