On Linux, the readlink utility accepts an option -f that follows additional links. This doesn't seem to work on Mac and possibly BSD based systems. What would the equivalent be?
Here's some debug information:
$ which readlink; readlink -f
/usr/bin/readlink
readlink: illegal option -f
usage: readlink [-n] [file ...]
I made a script called realpath personally which looks a little something like:
#!/usr/bin/env python
import os.sys
print os.path.realpath(sys.argv[1])
What about this?
function readlink() {
DIR="${1%/*}"
(cd "$DIR" && echo "$(pwd -P)")
}
greadlink is the gnu readlink that implements -f. You can use macports or others as well, I prefer homebrew.
I hate to pile on with yet another implementation, but I needed a) a portable, pure shell implementation, and b) unit-test coverage, as the number of edge-cases for something like this are non-trivial.
See my project on Github for tests and full code. What follows is a synopsis of the implementation:
As Keith Smith astutely points out, readlink -f does two things: 1) resolves symlinks recursively, and 2) canonicalizes the result, hence:
realpath() {
canonicalize_path "$(resolve_symlinks "$1")"
}
First, the symlink resolver implementation:
resolve_symlinks() {
local dir_context path
path=$(readlink -- "$1")
if [ $? -eq 0 ]; then
dir_context=$(dirname -- "$1")
resolve_symlinks "$(_prepend_path_if_relative "$dir_context" "$path")"
else
printf '%s\n' "$1"
fi
}
_prepend_path_if_relative() {
case "$2" in
/* ) printf '%s\n' "$2" ;;
* ) printf '%s\n' "$1/$2" ;;
esac
}
Note that this is a slightly simplified version of the full implementation. The full implementation adds a small check for symlink cycles, as well as massages the output a bit.
Finally, the function for canonicalizing a path:
canonicalize_path() {
if [ -d "$1" ]; then
_canonicalize_dir_path "$1"
else
_canonicalize_file_path "$1"
fi
}
_canonicalize_dir_path() {
(cd "$1" 2>/dev/null && pwd -P)
}
_canonicalize_file_path() {
local dir file
dir=$(dirname -- "$1")
file=$(basename -- "$1")
(cd "$dir" 2>/dev/null && printf '%s/%s\n' "$(pwd -P)" "$file")
}
That's it, more or less. Simple enough to paste into your script, but tricky enough that you'd be crazy to rely on any code that doesn't have unit tests for your use cases.
This is what I use:
stat -f %N $your_path
Perl has a readlink function (e.g. How do I copy symbolic links in Perl?). This works across most platforms, including OS X:
perl -e "print readlink '/path/to/link'"
For example:
$ mkdir -p a/b/c
$ ln -s a/b/c x
$ perl -e "print readlink 'x'"
a/b/c
POSIX compliant readlink -f implementation for POSIX shell scripts
https://github.com/ko1nksm/readlinkf
This is POSIX compliant (no bashism). It uses neither readlink nor realpath. I have verified that it is exactly the same by comparing with GNU readlink -f (see test results). It has error handling and good performance. You can safely replace from readlink -f. The license is CC0, so you can use it for any project.
This code is adopted in the bats-core project.
# POSIX compliant version
readlinkf_posix() {
[ "${1:-}" ] || return 1
max_symlinks=40
CDPATH='' # to avoid changing to an unexpected directory
target=$1
[ -e "${target%/}" ] || target=${1%"${1##*[!/]}"} # trim trailing slashes
[ -d "${target:-/}" ] && target="$target/"
cd -P . 2>/dev/null || return 1
while [ "$max_symlinks" -ge 0 ] && max_symlinks=$((max_symlinks - 1)); do
if [ ! "$target" = "${target%/*}" ]; then
case $target in
/*) cd -P "${target%/*}/" 2>/dev/null || break ;;
*) cd -P "./${target%/*}" 2>/dev/null || break ;;
esac
target=${target##*/}
fi
if [ ! -L "$target" ]; then
target="${PWD%/}${target:+/}${target}"
printf '%s\n' "${target:-/}"
return 0
fi
# `ls -dl` format: "%s %u %s %s %u %s %s -> %s\n",
# <file mode>, <number of links>, <owner name>, <group name>,
# <size>, <date and time>, <pathname of link>, <contents of link>
# https://pubs.opengroup.org/onlinepubs/9699919799/utilities/ls.html
link=$(ls -dl -- "$target" 2>/dev/null) || break
target=${link#*" $target -> "}
done
return 1
}
Please refer to the latest code. It may some fixed.
The easiest way to solve this problem and enable the functionality of readlink on Mac w/ Homebrew installed or FreeBSD is to install 'coreutils' package. May also be necessary on certain Linux distributions and other POSIX OS.
For example, in FreeBSD 11, I installed by invoking:
# pkg install coreutils
On MacOS with Homebrew, the command would be:
$ brew install coreutils
Not really sure why the other answers are so complicated, that's all there is to it. The files aren't in a different place, they're just not installed yet.
Begin Update
This is such a frequent problem that we have put together a Bash 4 library for free use (MIT License) called realpath-lib. This is designed to emulate readlink -f by default and includes two test suites to verify (1) that it works for a given unix system and (2) against readlink -f if installed (but this is not required). Additionally, it can be used to investigate, identify and unwind deep, broken symlinks and circular references, so it can be a useful tool for diagnosing deeply-nested physical or symbolic directory and file problems. It can be found at github.com or bitbucket.org.
End Update
Another very compact and efficient solution that does not rely on anything but Bash is:
function get_realpath() {
[[ ! -f "$1" ]] && return 1 # failure : file does not exist.
[[ -n "$no_symlinks" ]] && local pwdp='pwd -P' || local pwdp='pwd' # do symlinks.
echo "$( cd "$( echo "${1%/*}" )" 2>/dev/null; $pwdp )"/"${1##*/}" # echo result.
return 0 # success
}
This also includes an environment setting no_symlinks that provides the ability to resolve symlinks to the physical system. As long as no_symlinks is set to something, ie no_symlinks='on' then symlinks will be resolved to the physical system. Otherwise they will be applied (the default setting).
This should work on any system that provides Bash, and will return a Bash compatible exit code for testing purposes.
I wrote a realpath utility for OS X which can provide the same results as readlink -f.
Here is an example:
(jalcazar@mac tmp)$ ls -l a
lrwxrwxrwx 1 jalcazar jalcazar 11 8? 25 19:29 a -> /etc/passwd
(jalcazar@mac tmp)$ realpath a
/etc/passwd
If you are using MacPorts, you can install it with the following command: sudo port selfupdate && sudo port install realpath.
Since my work is used by people with non-BSD Linux as well as macOS, I've opted for using these aliases in our build scripts (sed included since it has similar issues):
##
# If you're running macOS, use homebrew to install greadlink/gsed first:
# brew install coreutils
#
# Example use:
# # Gets the directory of the currently running script
# dotfilesDir=$(dirname "$(globalReadlink -fm "$0")")
# alias al='pico ${dotfilesDir}/aliases.local'
##
function globalReadlink () {
# Use greadlink if on macOS; otherwise use normal readlink
if [[ $OSTYPE == darwin* ]]; then
greadlink "$@"
else
readlink "$@"
fi
}
function globalSed () {
# Use gsed if on macOS; otherwise use normal sed
if [[ $OSTYPE == darwin* ]]; then
gsed "$@"
else
sed "$@"
fi
}
Optional check you could add to automatically install homebrew + coreutils dependencies:
if [[ "$OSTYPE" == "darwin"* ]]; then
# Install brew if needed
if [ -z "$(which brew)" ]; then
/usr/bin/ruby -e "$(curl -fsSL https://raw.githubusercontent.com/Homebrew/install/master/install)";
fi
# Check for coreutils
if [ -z "$(brew ls coreutils)" ]; then
brew install coreutils
fi
fi
I suppose to be truly "global" it needs to check others...but that probably comes close to the 80/20 mark.
A simple one-liner in perl that's sure to work almost everywhere without any external dependencies:
perl -MCwd -e 'print Cwd::abs_path shift' ~/non-absolute/file
Will dereference symlinks.
Usage in a script could be like this:
readlinkf(){ perl -MCwd -e 'print Cwd::abs_path shift' "$1";}
ABSPATH="$(readlinkf ./non-absolute/file)"
The answer from @Keith Smith gives an infinite loop.
Here is my answer, which i use only on SunOS (SunOS miss so much POSIX and GNU commands).
It's a script file you have to put in one of your $PATH directories:
#!/bin/sh
! (($#)) && echo -e "ERROR: readlink <link to analyze>" 1>&2 && exit 99
link="$1"
while [ -L "$link" ]; do
lastLink="$link"
link=$(/bin/ls -ldq "$link")
link="${link##* -> }"
link=$(realpath "$link")
[ "$link" == "$lastlink" ] && echo -e "ERROR: link loop detected on $link" 1>&2 && break
done
echo "$link"
I have simply pasted the following to the top of my bash scripts:
#!/usr/bin/env bash -e
declare script=$(basename "$0")
declare dirname=$(dirname "$0")
declare scriptDir
if [[ $(uname) == 'Linux' ]];then
# use readlink -f
scriptDir=$(readlink -f "$dirname")
else
# can't use readlink -f, do a pwd -P in the script directory and then switch back
if [[ "$dirname" = '.' ]];then
# don't change directory, we are already inside
scriptDir=$(pwd -P)
else
# switch to the directory and then switch back
pwd=$(pwd)
cd "$dirname"
scriptDir=$(pwd -P)
cd "$pwd"
fi
fi
And removed all instances of readlink -f. $scriptDir and $script then will be available for the rest of the script.
While this does not follow all symlinks, it works on all systems and appears to be good enough for most use cases, it switches the directory into the containing folder, and then it does a pwd -P to get the real path of that directory, and then finally switch back to the original.
A lazy way that works for me,
$ brew install coreutils
$ ln -s /usr/local/bin/greadlink /usr/local/bin/readlink
$ which readlink
/usr/local/bin/readlink
/usr/bin/readlink
You may be interested in realpath(3), or Python's os.path.realpath. The two aren't exactly the same; the C library call requires that intermediary path components exist, while the Python version does not.
$ pwd
/tmp/foo
$ ls -l
total 16
-rw-r--r-- 1 miles wheel 0 Jul 11 21:08 a
lrwxr-xr-x 1 miles wheel 1 Jul 11 20:49 b -> a
lrwxr-xr-x 1 miles wheel 1 Jul 11 20:49 c -> b
$ python -c 'import os,sys;print(os.path.realpath(sys.argv[1]))' c
/private/tmp/foo/a
I know you said you'd prefer something more lightweight than another scripting language, but just in case compiling a binary is insufferable, you can use Python and ctypes (available on Mac OS X 10.5) to wrap the library call:
#!/usr/bin/python
import ctypes, sys
libc = ctypes.CDLL('libc.dylib')
libc.realpath.restype = ctypes.c_char_p
libc.__error.restype = ctypes.POINTER(ctypes.c_int)
libc.strerror.restype = ctypes.c_char_p
def realpath(path):
buffer = ctypes.create_string_buffer(1024) # PATH_MAX
if libc.realpath(path, buffer):
return buffer.value
else:
errno = libc.__error().contents.value
raise OSError(errno, "%s: %s" % (libc.strerror(errno), buffer.value))
if __name__ == '__main__':
print realpath(sys.argv[1])
Ironically, the C version of this script ought to be shorter. :)
FreeBSD and OSX have a version of statderived from NetBSD.
You can adjust the output with format switches (see the manual pages at the links above).
% cd /service
% ls -tal
drwxr-xr-x 22 root wheel 27 Aug 25 10:41 ..
drwx------ 3 root wheel 8 Jun 30 13:59 .s6-svscan
drwxr-xr-x 3 root wheel 5 Jun 30 13:34 .
lrwxr-xr-x 1 root wheel 30 Dec 13 2013 clockspeed-adjust -> /var/service/clockspeed-adjust
lrwxr-xr-x 1 root wheel 29 Dec 13 2013 clockspeed-speed -> /var/service/clockspeed-speed
% stat -f%R clockspeed-adjust
/var/service/clockspeed-adjust
% stat -f%Y clockspeed-adjust
/var/service/clockspeed-adjust
Some OS X versions of stat may lack the -f%R option for formats. In this case -stat -f%Y may suffice. The -f%Y option will show the target of a symlink, whereas -f%R shows the absolute pathname corresponding to the file.
EDIT:
If you're able to use Perl (Darwin/OS X comes installed with recent verions of perl) then:
perl -MCwd=abs_path -le 'print abs_path readlink(shift);' linkedfile.txt
will work.
There are already a lot of answers, but none worked for me... So this is what I'm using now.
readlink_f() {
local target="$1"
[ -f "$target" ] || return 1 #no nofile
while [ -L "$target" ]; do
target="$(readlink "$target")"
done
echo "$(cd "$(dirname "$target")"; pwd -P)/$target"
}
The paths to readlink are different between my system and yours. Please try specifying the full path:
/sw/sbin/readlink -f
MacPorts and Homebrew provide a coreutils package containing greadlink (GNU readlink). Credit to Michael Kallweitt post in mackb.com.
brew install coreutils
greadlink -f file.txt
Truely platform-indpendent would be also this R-onliner
readlink(){ RScript -e "cat(normalizePath(commandArgs(T)[1]))" "$1";}
To actually mimic readlink -f <path>, $2 instead of $1 would need to be used.
Here is a portable shell function that should work in ANY Bourne comparable shell. It will resolve the relative path punctuation ".. or ." and dereference symbolic links.
If for some reason you do not have a realpath(1) command, or readlink(1) this can be aliased.
which realpath || alias realpath='real_path'
Enjoy:
real_path () {
OIFS=$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
## Resolve symbolic links
if [ -h "$FOO" ]
then
IFS=$OIFS
set `ls -l "$FOO"`
while shift ;
do
if [ "$1" = "->" ]
then FOO=$2
shift $#
break
fi
done
IFS='/'
fi
done
IFS=$OIFS
echo "$FOO"
}
also, just in case anybody is interested here is how to implement basename and dirname in 100% pure shell code:
## http://www.opengroup.org/onlinepubs/000095399/functions/dirname.html
# the dir name excludes the least portion behind the last slash.
dir_name () {
echo "${1%/*}"
}
## http://www.opengroup.org/onlinepubs/000095399/functions/basename.html
# the base name excludes the greatest portion in front of the last slash.
base_name () {
echo "${1##*/}"
}
You can find updated version of this shell code at my google site: http://sites.google.com/site/jdisnard/realpath
EDIT: This code is licensed under the terms of the 2-clause (freeBSD style) license. A copy of the license may be found by following the above hyperlink to my site.
Better late than never, I suppose. I was motivated to develop this specifically because my Fedora scripts weren't working on the Mac. The problem is dependencies and Bash. Macs don't have them, or if they do, they are often somewhere else (another path). Dependency path manipulation in a cross-platform Bash script is a headache at best and a security risk at worst - so it's best to avoid their use, if possible.
The function get_realpath() below is simple, Bash-centric, and no dependencies are required. I uses only the Bash builtins echo and cd. It is also fairly secure, as everything gets tested at each stage of the way and it returns error conditions.
If you don't want to follow symlinks, then put set -P at the front of the script, but otherwise cd should resolve the symlinks by default. It's been tested with file arguments that are {absolute | relative | symlink | local} and it returns the absolute path to the file. So far we've not had any problems with it.
function get_realpath() {
if [[ -f "$1" ]]
then
# file *must* exist
if cd "$(echo "${1%/*}")" &>/dev/null
then
# file *may* not be local
# exception is ./file.ext
# try 'cd .; cd -;' *works!*
local tmppwd="$PWD"
cd - &>/dev/null
else
# file *must* be local
local tmppwd="$PWD"
fi
else
# file *cannot* exist
return 1 # failure
fi
# reassemble realpath
echo "$tmppwd"/"${1##*/}"
return 0 # success
}
You can combine this with other functions get_dirname, get_filename, get_stemname and validate_path. These can be found at our GitHub repository as realpath-lib (full disclosure - this is our product but we offer it free to the community without any restrictions). It also could serve as a instructional tool - it's well documented.
We've tried our best to apply so-called 'modern Bash' practices, but Bash is a big subject and I'm certain there will always be room for improvement. It requires Bash 4+ but could be made to work with older versions if they are still around.
Implementation
Follow the instructions at https://brew.sh/
brew install coreutils
You can place your alias in ~/.bashrc, ~/.bash_profile, or wherever you are used to keeping your bash aliases. I personally keep mine in ~/.bashrc
alias readlink=greadlink
You can create similar aliases for other coreutils such as gmv, gdu, gdf, and so on. But beware that the GNU behavior on a mac machine may be confusing to others used to working with native coreutils, or may behave in unexpected ways on your mac system.
Explanation
coreutils is a brew package that installs GNU/Linux core utilities which correspond to the Mac OSX implementation of them so that you can use those
You may find programs or utilties on your mac osx system which seem similar to Linux coreutils ("Core Utilities") yet they differ in some ways (such as having different flags).
This is because the Mac OSX implementation of these tools are different. To get the original GNU/Linux-like behavior you can install the coreutils package via the brew package management system.
This will install corresponding core utilities, prefixed by g. E.g. for readlink, you will find a corresponding greadlink program.
In order to make readlink perform like the GNU readlink (greadlink) implementation, you can make a simple alias after you install coreutils.
Source: Stackoverflow.com