Bash script absolute path with OS X

I am trying to obtain the absolute path to the currently running script on OS X.

I saw many replies going for readlink -f $0. However since OS X's readlink is the same as BSD's, it just doesn't work (it works with GNU's version).

Is there an out-of-the-box solution to this?

These three simple steps are going to solve this and many other OS X issues:

1. Install Homebrew
2. brew install coreutils
3. grealpath .

(3) may be changed to just realpath, see (2) output

There's a realpath() C function that'll do the job, but I'm not seeing anything available on the command-line. Here's a quick and dirty replacement:

#!/bin/bash

realpath() {
    [[ $1 = /* ]] && echo "$1" || echo "$PWD/${1#./}"
}

realpath "$0"

This prints the path verbatim if it begins with a /. If not it must be a relative path, so it prepends $PWD to the front. The #./ part strips off ./ from the front of $1.

I found the answer a bit wanting for a few reasons:
in particular, they don't resolve multiple levels of symbolic links, and they are extremely "Bash-y".

While the original question does explicitly ask for a "Bash script", it also makes mention of Mac OS X's BSD-like, non-GNU readlink.

So here's an attempt at some reasonable portability (I've checked it with bash as 'sh' and dash), resolving an arbitrary number of symbolic links; and it should also work with whitespace in the path(s).

This answer was previously edited, re-adding the local bashism. The point of this answer is a portable, POSIX solution. I have edited it to address variable scoping by changing it to a subshell function, rather than an inline one. Please do not edit.

#!/bin/sh
realpath() (
  OURPWD=$PWD
  cd "$(dirname "$1")"
  LINK=$(readlink "$(basename "$1")")
  while [ "$LINK" ]; do
    cd "$(dirname "$LINK")"
    LINK=$(readlink "$(basename "$1")")
  done
  REALPATH="$PWD/$(basename "$1")"
  cd "$OURPWD"
  echo "$REALPATH"
)
realpath "$@"

Hope that can be of some use to someone.

A more command-line-friendly variant of the Python solution:

python -c 'import os, sys; print(os.path.realpath(sys.argv[1]))' ./my/path

Since there is a [realpath](http://man7.org/linux/man-pages/man3/realpath.3.html "realpath") as others have pointed out:

// realpath.c
#include <stdio.h>
#include <stdlib.h>

int main (int argc, char* argv[])
{
  if (argc > 1) {
    for (int argIter = 1; argIter < argc; ++argIter) {
      char *resolved_path_buffer = NULL;
      char *result = realpath(argv[argIter], resolved_path_buffer);

      puts(result);

      if (result != NULL) {
        free(result);
      }
    }
  }

  return 0;
}

Makefile:

#Makefile
OBJ = realpath.o

%.o: %.c
	  $(CC) -c -o $@ $< $(CFLAGS)

realpath: $(OBJ)
	  gcc -o $@ $^ $(CFLAGS)

Then compile with make and put in a soft link with:
ln -s $(pwd)/realpath /usr/local/bin/realpath

I was looking for a solution for use in a system provision script, i.e., run before Homebrew is even installed. Lacking a proper solution I'd just offload the task to a cross-platform language, e.g., Perl:

script_abspath=$(perl -e 'use Cwd "abs_path"; print abs_path(@ARGV[0])' -- "$0")

More often what we actually want is the containing directory:

here=$(perl -e 'use File::Basename; use Cwd "abs_path"; print dirname(abs_path(@ARGV[0]));' -- "$0")

Use Python to get it:

#!/usr/bin/env python
import os
import sys

print(os.path.realpath(sys.argv[1]))

abs_path () {    
   echo "$(cd $(dirname "$1");pwd)/$(basename "$1")"
}

dirname will give the directory name of /path/to/file, i.e. /path/to.

cd /path/to; pwd ensures that the path is absolute.

basename will give just the filename in /path/to/file, i.e.file.

realpath for Mac OS X

realpath() {
    path=`eval echo "$1"`
    folder=$(dirname "$path")
    echo $(cd "$folder"; pwd)/$(basename "$path"); 
}

Example with related path:

realpath "../scripts/test.sh"

Example with home folder

realpath "~/Test/../Test/scripts/test.sh"

I checked every answered, but missed the best one (IMHO) by Jason S Jul 14 '16 at 3:12, left the comment field.

So here it is, in case someone like me having the tendency to check answered and don't have time to go through every single comments:

$( cd "$(dirname "$0")" ; pwd -P )

Help:

NAME
     pwd -- return working directory name

SYNOPSIS
     pwd [-L | -P]

DESCRIPTION
     The pwd utility writes the absolute pathname of the current working
     directory to the standard output.

     Some shells may provide a builtin pwd command which is similar or identi-
     cal to this utility.  Consult the builtin(1) manual page.

     The options are as follows:

     -L      Display the logical current working directory.

     -P      Display the physical current working directory (all symbolic
             links resolved).

So as you can see above, I took a shot at this about 6 months ago. I totally forgot about it until I found myself in need of a similar thing again. I was completely shocked to see just how rudimentary it was; I've been teaching myself to code pretty intensively for about a year now, but I often feel like maybe I haven't learned anything at all when things are at their worst.

I would remove the 'solution' above, but I really like it sort of being a record of of how much I really have learnt over the past few months.

But I digress. I sat down and worked it all out last night. The explanation in the comments should be sufficient. If you want to track the copy I'm continuing to work on, you can follow this gist. This probably does what you need.

#!/bin/sh # dash bash ksh # !zsh (issues). G. Nixon, 12/2013. Public domain.

## 'linkread' or 'fullpath' or (you choose) is a little tool to recursively
## dereference symbolic links (ala 'readlink') until the originating file
## is found. This is effectively the same function provided in stdlib.h as
## 'realpath' and on the command line in GNU 'readlink -f'.

## Neither of these tools, however, are particularly accessible on the many
## systems that do not have the GNU implementation of readlink, nor ship
## with a system compiler (not to mention the requisite knowledge of C).

## This script is written with portability and (to the extent possible, speed)
## in mind, hence the use of printf for echo and case statements where they
## can be substituded for test, though I've had to scale back a bit on that.

## It is (to the best of my knowledge) written in standard POSIX shell, and
## has been tested with bash-as-bin-sh, dash, and ksh93. zsh seems to have
## issues with it, though I'm not sure why; so probably best to avoid for now.

## Particularly useful (in fact, the reason I wrote this) is the fact that
## it can be used within a shell script to find the path of the script itself.
## (I am sure the shell knows this already; but most likely for the sake of
## security it is not made readily available. The implementation of "$0"
## specificies that the $0 must be the location of **last** symbolic link in
## a chain, or wherever it resides in the path.) This can be used for some
## ...interesting things, like self-duplicating and self-modifiying scripts.

## Currently supported are three errors: whether the file specified exists
## (ala ENOENT), whether its target exists/is accessible; and the special
## case of when a sybolic link references itself "foo -> foo": a common error
## for beginners, since 'ln' does not produce an error if the order of link
## and target are reversed on the command line. (See POSIX signal ELOOP.)

## It would probably be rather simple to write to use this as a basis for
## a pure shell implementation of the 'symlinks' util included with Linux.

## As an aside, the amount of code below **completely** belies the amount
## effort it took to get this right -- but I guess that's coding for you.

##===-------------------------------------------------------------------===##

for argv; do :; done # Last parameter on command line, for options parsing.

## Error messages. Use functions so that we can sub in when the error occurs.

recurses(){ printf "Self-referential:\n\t$argv ->\n\t$argv\n" ;}
dangling(){ printf "Broken symlink:\n\t$argv ->\n\t"$(readlink "$argv")"\n" ;}
errnoent(){ printf "No such file: "$@"\n" ;} # Borrow a horrible signal name.

# Probably best not to install as 'pathfull', if you can avoid it.

pathfull(){ cd "$(dirname "$@")"; link="$(readlink "$(basename "$@")")"

## 'test and 'ls' report different status for bad symlinks, so we use this.

 if [ ! -e "$@" ]; then if $(ls -d "$@" 2>/dev/null) 2>/dev/null;  then
    errnoent 1>&2; exit 1; elif [ ! -e "$@" -a "$link" = "$@" ];   then
    recurses 1>&2; exit 1; elif [ ! -e "$@" ] && [ ! -z "$link" ]; then
    dangling 1>&2; exit 1; fi
 fi

## Not a link, but there might be one in the path, so 'cd' and 'pwd'.

 if [ -z "$link" ]; then if [ "$(dirname "$@" | cut -c1)" = '/' ]; then
   printf "$@\n"; exit 0; else printf "$(pwd)/$(basename "$@")\n"; fi; exit 0
 fi

## Walk the symlinks back to the origin. Calls itself recursivly as needed.

 while [ "$link" ]; do
   cd "$(dirname "$link")"; newlink="$(readlink "$(basename "$link")")"
   case "$newlink" in
    "$link") dangling 1>&2 && exit 1                                       ;;
         '') printf "$(pwd)/$(basename "$link")\n"; exit 0                 ;;
          *) link="$newlink" && pathfull "$link"                           ;;
   esac
 done
 printf "$(pwd)/$(basename "$newlink")\n"
}

## Demo. Install somewhere deep in the filesystem, then symlink somewhere 
## else, symlink again (maybe with a different name) elsewhere, and link
## back into the directory you started in (or something.) The absolute path
## of the script will always be reported in the usage, along with "$0".

if [ -z "$argv" ]; then scriptname="$(pathfull "$0")"

# Yay ANSI l33t codes! Fancy.
 printf "\n\033[3mfrom/as: \033[4m$0\033[0m\n\n\033[1mUSAGE:\033[0m   "
 printf "\033[4m$scriptname\033[24m [ link | file | dir ]\n\n         "
 printf "Recursive readlink for the authoritative file, symlink after "
 printf "symlink.\n\n\n         \033[4m$scriptname\033[24m\n\n        "
 printf " From within an invocation of a script, locate the script's "
 printf "own file\n         (no matter where it has been linked or "
 printf "from where it is being called).\n\n"

else pathfull "$@"
fi

On macOS, the only solution that I've found to this that reliably handles symlinks is by using realpath. Since this requires brew install coreutils, I just automated that step. My implementation looks like this:

#!/usr/bin/env bash

set -e

if ! which realpath >&/dev/null; then
  if ! which brew >&/dev/null; then
    msg="ERROR: This script requires brew. See https://brew.sh for installation instructions."
    echo "$(tput setaf 1)$msg$(tput sgr0)" >&2
    exit 1
  fi
  echo "Installing coreutils/realpath"
  brew install coreutils >&/dev/null
fi

thisDir=$( dirname "`realpath "$0"`" )
echo "This script is run from \"$thisDir\""

This errors if they don't have brew installed, but you could alternatively just install that too. I just didn't feel comfortable automating something that curls arbitrary ruby code from the net.

Note that this an automated variation on Oleg Mikheev's answer.

---

One important test

One good test of any of these solutions is:

1. put the code in a script file somewhere
2. in another directory, symlink (ln -s) to that file
3. run the script from that symlink

Does the solution dereference the symlink, and give you the original directory? If so, it works.

This seems to work for OSX, doesnt require any binaries, and was pulled from here

function normpath() {
  # Remove all /./ sequences.
  local path=${1//\/.\//\/}

  # Remove dir/.. sequences.
  while [[ $path =~ ([^/][^/]*/\.\./) ]]; do
    path=${path/${BASH_REMATCH[0]}/}
  done
  echo $path
}

I like this:

#!/usr/bin/env bash
function realpath() {
    local _X="$PWD"
    local _LNK=$1
    cd "$(dirname "$_LNK")"
    if [ -h "$_LNK" ]; then
        _LNK="$(readlink "$_LNK")"
        cd "$(dirname "$_LNK")"
    fi
    echo "$PWD/$(basename "$_LNK")"
    cd "$_X"
}

I needed a realpath replacement on OS X, one that operates correctly on paths with symlinks and parent references just like readlink -f would. This includes resolving symlinks in the path before resolving parent references; e.g. if you have installed the homebrew coreutils bottle, then run:

$ ln -s /var/log/cups /tmp/linkeddir  # symlink to another directory
$ greadlink -f /tmp/linkeddir/..      # canonical path of the link parent
/private/var/log

Note that readlink -f has resolved /tmp/linkeddir before resolving the .. parent dir reference. Of course, there is no readlink -f on Mac either.

So as part of the a bash implementation for realpath I re-implemented what a GNUlib canonicalize_filename_mode(path, CAN_ALL_BUT_LAST) function call does, in Bash 3.2; this is also the function call that GNU readlink -f makes:

# shellcheck shell=bash
set -euo pipefail

_contains() {
	# return true if first argument is present in the other arguments
	local elem value

	value="$1"
	shift

	for elem in "$@"; do 
		if [[ $elem == "$value" ]]; then
			return 0
		fi
	done
	return 1
}

_canonicalize_filename_mode() {
	# resolve any symlink targets, GNU readlink -f style
	# where every path component except the last should exist and is
	# resolved if it is a symlink. This is essentially a re-implementation
	# of canonicalize_filename_mode(path, CAN_ALL_BUT_LAST).
	# takes the path to canonicalize as first argument

	local path result component seen
	seen=()
	path="$1"
	result="/"
	if [[ $path != /* ]]; then  # add in current working dir if relative
		result="$PWD"
	fi
	while [[ -n $path ]]; do
		component="${path%%/*}"
		case "$component" in
			'') # empty because it started with /
				path="${path:1}" ;;
			.)  # ./ current directory, do nothing
				path="${path:1}" ;;
			..) # ../ parent directory
				if [[ $result != "/" ]]; then  # not at the root?
					result="${result%/*}"      # then remove one element from the path
				fi
				path="${path:2}" ;;
			*)
				# add this component to the result, remove from path
				if [[ $result != */ ]]; then
					result="$result/"
				fi
				result="$result$component"
				path="${path:${#component}}"
				# element must exist, unless this is the final component
				if [[ $path =~ [^/] && ! -e $result ]]; then
					echo "$1: No such file or directory" >&2
					return 1
				fi
				# if the result is a link, prefix it to the path, to continue resolving
				if [[ -L $result ]]; then
					if _contains "$result" "${seen[@]+"${seen[@]}"}"; then
						# we've seen this link before, abort
						echo "$1: Too many levels of symbolic links" >&2
						return 1
					fi
					seen+=("$result")
					path="$(readlink "$result")$path"
					if [[ $path = /* ]]; then
						# if the link is absolute, restart the result from /
						result="/"
					elif [[ $result != "/" ]]; then
						# otherwise remove the basename of the link from the result
						result="${result%/*}"
					fi
				elif [[ $path =~ [^/] && ! -d $result ]]; then
					# otherwise all but the last element must be a dir
					echo "$1: Not a directory" >&2
					return 1
				fi
				;;
		esac
	done
	echo "$result"
}

It includes circular symlink detection, exiting if the same (intermediary) path is seen twice.

If all you need is readlink -f, then you can use the above as:

readlink() {
    if [[ $1 != -f ]]; then  # poor-man's option parsing
        # delegate to the standard readlink command
        command readlink "$@"
        return
    fi

    local path result seenerr
    shift
    seenerr=
    for path in "$@"; do
        # by default readlink suppresses error messages
        if ! result=$(_canonicalize_filename_mode "$path" 2>/dev/null); then
            seenerr=1
            continue
        fi
        echo "$result"
    done
    if [[ $seenerr ]]; then
        return 1;
    fi
}

For realpath, I also needed --relative-to and --relative-base support, which give you relative paths after canonicalizing:

_realpath() {
    # GNU realpath replacement for bash 3.2 (OS X)
    # accepts --relative-to= and --relative-base options
    # and produces canonical (relative or absolute) paths for each
    # argument on stdout, errors on stderr, and returns 0 on success
    # and 1 if at least 1 path triggered an error.

	local relative_to relative_base seenerr path

	relative_to=
	relative_base=
	seenerr=

	while [[ $# -gt 0 ]]; do
		case $1 in
			"--relative-to="*)
				relative_to=$(_canonicalize_filename_mode "${1#*=}")
				shift 1;;
			"--relative-base="*)
				relative_base=$(_canonicalize_filename_mode "${1#*=}")
				shift 1;;
			*)
				break;;
		esac
	done

	if [[
		-n $relative_to
		&& -n $relative_base
		&& ${relative_to#${relative_base}/} == "$relative_to"
	]]; then
		# relative_to is not a subdir of relative_base -> ignore both
		relative_to=
		relative_base=
	elif [[ -z $relative_to && -n $relative_base ]]; then
		# if relative_to has not been set but relative_base has, then
		# set relative_to from relative_base, simplifies logic later on
		relative_to="$relative_base"
	fi

	for path in "$@"; do
		if ! real=$(_canonicalize_filename_mode "$path"); then
			seenerr=1
			continue
		fi

		# make path relative if so required
		if [[
			-n $relative_to
			&& ( # path must not be outside relative_base to be made relative
				-z $relative_base || ${real#${relative_base}/} != "$real"
			)
		]]; then
			local common_part parentrefs

			common_part="$relative_to"
			parentrefs=
			while [[ ${real#${common_part}/} == "$real" ]]; do
				common_part="$(dirname "$common_part")"
				parentrefs="..${parentrefs:+/$parentrefs}"
			done

			if [[ $common_part != "/" ]]; then
				real="${parentrefs:+${parentrefs}/}${real#${common_part}/}"
			fi
		fi

		echo "$real"
	done
	if [[ $seenerr ]]; then
		return 1
	fi
}

if ! command -v realpath > /dev/null 2>&1; then
	# realpath is not available on OSX unless you install the `coreutils` brew
	realpath() { _realpath "$@"; }
fi

I included unit tests in my Code Review request for this code.

For those nodejs developers in a mac using bash:

realpath() {
  node -p "fs.realpathSync('$1')"
}

Based on the communication with commenter, I agreed that it is very hard and has no trival way to implement a realpath behaves totally same as Ubuntu.

But the following version, can handle corner cases best answer can't and satisfy my daily needs on macbook. Put this code into your ~/.bashrc and remember:

• arg can only be 1 file or dir, no wildcard
• no spaces in the dir or file name
• at least the file or dir's parent dir exists
• feel free to use . .. / thing, these are safe

---

    # 1. if is a dir, try cd and pwd
    # 2. if is a file, try cd its parent and concat dir+file
    realpath() {
     [ "$1" = "" ] && return 1

     dir=`dirname "$1"`
     file=`basename "$1"`

     last=`pwd`
 
     [ -d "$dir" ] && cd $dir || return 1
     if [ -d "$file" ];
     then
       # case 1
       cd $file && pwd || return 1
     else
       # case 2
       echo `pwd`/$file | sed 's/\/\//\//g'
     fi
 
     cd $last
    }