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Given that realpath command does not exists on every unix platform, I would like to replace realpath with readlink command in order to make my shell script as cross-platform as possible.

The thing is that realpath has the --relative-to parameter which is necessary in my case:

$ realpath bdd/full --relative-to bdd
full

on the other hand, readlink seems to provide only the main functionality of realpath command:

$ readlink -f bdd/full
/home/user/bdd/full

After reading the man page, I couldn't find any parameter similar to --relative-to.

Have you any idea if readlink supports a --relative-to-like functionality and if it's not, is there any "clean" way to achive such thing using readlink or any other cross-platform command?

UPDATE:

In my case, --relative-to is necessary for logging purposes, in my shell script, the user passes two relative paths, the relative of the base folder and the relative path of the file on which the action will be performed. In order to print a more-human friendly log entry, I want to print the relative path of file from the base folder path.

I'm currently using the following function to achive my goal:

get_relative_path () {
  if command -v realpath &> /dev/null
  then
    realpath --relative-to="${2-$PWD}" "$1"
  else
    python -c 'import os.path, sys;print os.path.relpath(sys.argv[1],sys.argv[2])' "$1" "${2-$PWD}"
  fi
}
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  • Could you give us some more details on why you need this? readlink doesn't have any equivalent to --relative-to, but if you explain why you need it, we might be able to come up with a workaround.
    – terdon
    Commented Mar 15, 2021 at 16:58
  • There seems not to be any easy alternative to realpath: see, for instance unix.stackexchange.com/q/85060/315749 or stackoverflow.com/q/2564634/10488700 on Stack Overflow
    – fra-san
    Commented Mar 15, 2021 at 17:42
  • Your example gives the same output as say basename PATH - are you just trying to get the last element? or do you intend something else? Unfortunately this is a difficult problem to solve for large numbers of platforms - for instance on OSX readlink doesn't have -f option
    – Mr R
    Commented Mar 15, 2021 at 20:25
  • @terdon check out the update for further details Commented Mar 16, 2021 at 10:00
  • @MrR basename is not enough in my case, file might be inside multiple sub-folders. You are right, I didn't know how difficult is to implement a cross-platform shell script :P Commented Mar 16, 2021 at 10:01

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