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Top Forums Shell Programming and Scripting Running program and output files in specific directories Post 303013250 by Don Cragun on Sunday 18th of February 2018 06:31:33 PM
Old 02-18-2018
Quote:
Originally Posted by kristinu
... ... ...

I get the same results

Code:
dir=$(dirname "$fn")
fnm=$(basename "$fn")

as doing

Code:
dir=${fn%/*}
fnm=${fn##*/}

How is one faster than the latter? What does `dirname` and `basename` work?

I did a test and variable substitution is faster as you say.
Your code uses command substitution (i.e., $(command arguments)). That involves forking a shell, executing command, waiting for command to finish, reading the results from command, and assigning them to a variable.

My code uses variable expansion which is done entirely in the shell. The fork and exec done by command substitution is a very slow shell operation. The string manipulations done by variable expansions are much faster.
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DH_INSTALLDEB(1)						     Debhelper							  DH_INSTALLDEB(1)

NAME
dh_installdeb - install files into the DEBIAN directory SYNOPSIS
dh_installdeb [debhelperoptions] DESCRIPTION
dh_installdeb is a debhelper program that is responsible for installing files into the DEBIAN directories in package build directories with the correct permissions. FILES
package.postinst package.preinst package.postrm package.prerm These maintainer scripts are installed into the DEBIAN directory. Inside the scripts, the token #DEBHELPER# is replaced with shell script snippets generated by other debhelper commands. package.triggers package.shlibs These control files are installed into the DEBIAN directory. package.conffiles This control file will be installed into the DEBIAN directory. In v3 compatibility mode and higher, all files in the etc/ directory in a package will automatically be flagged as conffiles by this program, so there is no need to list them manually here. package.maintscript Lines in this file correspond to dpkg-maintscript-helper(1) commands and parameters. Any shell metacharacters will be escaped, so arbitrary shell code cannot be inserted here. For example, a line such as "mv_conffile /etc/oldconffile /etc/newconffile" will insert maintainer script snippets into all maintainer scripts sufficient to move that conffile. A versioned Pre-Dependency on dpkg is needed to use dpkg-maintscript-helper(1). An appropriate Pre-Dependency is set in ${misc:Pre-Depends} ; you should make sure to put that token into an appropriate place in your debian/control file. SEE ALSO
debhelper(7) This program is a part of debhelper. AUTHOR
Joey Hess <joeyh@debian.org> 8.9.0ubuntu2.1 2012-06-12 DH_INSTALLDEB(1)
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