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Full Discussion: Running program and output files in specific directories
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.
This User Gave Thanks to Don Cragun For This Post:
kristinu
 

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LEARN ABOUT OPENSOLARIS

dirname

basename(1)							   User Commands						       basename(1)

NAME

       basename, dirname - deliver portions of path names

SYNOPSIS

       /usr/bin/basename string [suffix]

       /usr/xpg4/bin/basename string [suffix]

       dirname string

DESCRIPTION

       The  basename  utility deletes any prefix ending in / and the suffix (if present in string) from string, and prints the result on the stan-
       dard output. It is normally used inside substitution marks (``) within shell procedures.

   /usr/bin
       The suffix is a pattern defined on the expr(1) manual page.

   /usr/xpg4/bin
       The suffix is a string with no special significance attached to	any of the characters it contains.

       The dirname utility delivers all but the last level of the path name in string.

EXAMPLES

       Example 1 Setting environment variables

       The following example, invoked with the argument /home/sms/personal/mail sets the environment variable NAME to the file named mail and  the
       environment variable MYMAILPATH to the string  /home/sms/personal:

	 example% NAME=`basename $HOME/personal/mail`
	 example% MYMAILPATH=`dirname $HOME/personal/mail`

       Example 2 Compiling a file and moving the output

       This  shell  procedure,	invoked  with  the argument /usr/src/bin/cat.c, compiles the named file and moves the output to cat in the current
       directory:

	 example% cc $1
	 example% mv a.out `basename $1 .c`

ENVIRONMENT VARIABLES

       See environ(5) for descriptions of the following environment variables that affect  the execution of basename and  dirname:  LANG,  LC_ALL,
       LC_CTYPE, LC_MESSAGES, and NLSPATH.

EXIT STATUS

       The following exit values are returned:

       0     Successful completion.

       >0    An error occurred.

ATTRIBUTES

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

   /usr/bin
       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWcsu			   |
       +-----------------------------+-----------------------------+

   /usr/xpg4/bin
       +-----------------------------+-----------------------------+
       |      ATTRIBUTE TYPE	     |	    ATTRIBUTE VALUE	   |
       +-----------------------------+-----------------------------+
       |Availability		     |SUNWxcu4			   |
       +-----------------------------+-----------------------------+
       |Interface Stability	     |Standard			   |
       +-----------------------------+-----------------------------+

SEE ALSO

       expr(1), basename(3C), attributes(5), environ(5), standards(5)

SunOS 5.11							    18 Mar 1997 						       basename(1)
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