Maipulating path names

real_path ()

Sometimes the Path Working Directory (pwd) contains relative path punctuation, two dots for the parent directory, or one dot for the current directory.
There may also be symbolic links on the file node, or any part of the directory portion of the path hierarchy.

For now this code will clean any "..", "." or redundant "/" characters.
This emulates the POSIX realpath() function in shell code.
This makes one sub-shell exec to ls(1) making it not 100% pure shell code, but there is no way to dereference symbolic links otherwise.
real_path () {
  OIFS=$IFS
  IFS='/'
  for I in $1
  do
    # Resolve relative path punctuation.
    if [ "$I" = "." ] || [ -z "$I" ]
      then continue
    elif [ "$I" = ".." ]
      then FOO="${FOO%%/${FOO##*/}}"
           continue
      else FOO="${FOO}/${I}"
    fi

    # Dereference symbolic links.
    if [ -h "$FOO" ] && [ -x "/bin/ls" ]
then IFS=$OIFS set `/bin/ls -l "$FOO"` while shift ; do if [ "$1" = "->" ] then FOO=$2 shift $# break fi done fi done IFS=$OIFS echo "$FOO" }


dir_name ()

Takes a pathname, and return a string that is a pathname of the parent directory of that file.
This emulates the POSIX dirname() function definition in portable shell code.
dir_name () {
  echo "${1%/*}"
}


base_name ()

Take a pathname, and return the final component of the pathname.
This emulates the POSIX basename() function definition in portable shell code.
base_name () {
echo "${1##*/}"
}




Usage:

For interactive use an alias of the functions when the actual command is absent:
which realpath || alias realpath='real_path'
which dirnameĀ  || alias dirname='dir_name'
which basename || alias basename='base_name'

For general purpose use:
  • The functions can be placed in files that are sourced as part of the shell function path ($FPATH).
  • Integrated into the shell setup (dot) files.
  • Integrated or sourced from scripts directly.

The real_path function will disambiguate relative paths.
real_path /.//usr/local.//../././bin/.
/usr/bin


When using the dir_name function, I always like to use it in conjunction with real_path.
dir_name $(real_path /.//usr/local.//../././bin/.//)
/usr

When using the base_name function it will always return the last file or directory part of the path given on input.
base_name $(real_path /.//usr/local.//../././bin/.//)
bin

It is not necessary to use real_path with any of these, especially base_name.
base_name /usr/bin/snmpget
snmpget



LICENSE:

The following is a 2-clause BSD license.

Copyright 2010 Jon Disnard. All rights reserved.

Redistribution and use in source and binary forms, with or without modification, are
permitted provided that the following conditions are met:

1. Redistributions of source code must retain the above copyright notice, this list of
conditions and the following disclaimer.

2. Redistributions in binary form must reproduce the above copyright notice, this list
of conditions and the following disclaimer in the documentation and/or other materials
provided with the distribution.

THIS SOFTWARE IS PROVIDED BY Jon Disnard ``AS IS'' AND ANY EXPRESS OR IMPLIED
WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND
FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL <COPYRIGHT HOLDER> OR
CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING
NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF
ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

The views and conclusions contained in the software and documentation are those of the
authors and should not be interpreted as representing official policies, either expressed
or implied, of Jon Disnard.



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