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Top Forums Shell Programming and Scripting Unsure of sed notation (nu\\t.\*) Post 302540464 by alister on Wednesday 20th of July 2011 04:52:58 PM
Old 07-20-2011
Quote:
Originally Posted by czar21
Code:
sed s:nu\\t.\*:"nu=0"

You must have garbled the code while posting. That's not a valid sed command since the substitute command is unterminated.

If we add a : at the end, then at least we have something that makes sense to at least one sed implementation, GNU sed. Even so, I'm inclined to believe that whoever wrote that is deranged and/or trying to intentionally confuse the reader.

If single quotes were used to protect the sed script, all but one of the backslashes and all of the double quotes would not be needed. There's also no need to use the non-default delimiter (colon) since there are no forward slashes in the command. A much clearer version:
Code:
sed 's/nu\t.*/nu=0/'

What does that mean then? \t is an undefined sequence in POSIX sed. GNU sed treats it as an extension which matches a tab character. So, assuming GNU sed, it replaces nu<tab><optional misc characters><end of line> with nu=0<end of line>.

Regards,
Alister
 

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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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