How can I get the behavior of GNU s readlink -f on a Mac

Question

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

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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.

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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

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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

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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     - gt             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

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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

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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 gt  dev null  amp  amp  pwd -P                  canonicalize file path         local dir file     dir   dirname --   1       file   basename --   1        cd   dir  2 gt  dev null  amp  amp  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

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This is what I use   stat -f  N  your path

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I have simply pasted the following to the top of my bash scripts     usr bin env bash -e  declare script   basename  quot  0 quot   declare dirname   dirname  quot  0 quot   declare scriptDir if      uname      Linux     then       use readlink -f     scriptDir   readlink -f  quot  dirname quot   else       can t use readlink -f  do a pwd -P in the script directory and then switch back     if     quot  dirname quot           then           don t change directory  we are already inside         scriptDir   pwd -P      else           switch to the directory and then switch back         pwd   pwd          cd  quot  dirname quot          scriptDir   pwd -P          cd  quot  pwd quot      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

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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      amp  amp  return 1   failure   file does not exist         -n   no symlinks      amp  amp  local pwdp  pwd -P     local pwdp  pwd    do symlinks      echo     cd     echo    1         2 gt  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

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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 - gt  a lrwxr-xr-x  1 miles    wheel  1 Jul 11 20 49 c - gt  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

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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         amp  gt  dev null     then           file  may  not be local           exception is   file ext           try  cd    cd -    works           local tmppwd   PWD          cd -  amp  gt  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

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Truely platform-indpendent would be also this R-onliner  readlink    RScript -e  cat normalizePath commandArgs T  1       1      To actually mimic readlink -f  lt path gt    2 instead of  1 would need to be used

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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

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readlink -f does two things    It iterates along a sequence of symlinks until it finds an actual file  It returns that file s canonicalized name mdash i e   its absolute pathname    If you want to  you can just build a shell script that uses vanilla readlink behavior to achieve the same thing   Here s an example   Obviously you could insert this in your own script where you d like to call readlink -f      bin sh  TARGET FILE  1  cd  dirname  TARGET FILE  TARGET FILE  basename  TARGET FILE     Iterate down a  possible  chain of symlinks while   -L   TARGET FILE    do     TARGET FILE  readlink  TARGET FILE      cd  dirname  TARGET FILE      TARGET FILE  basename  TARGET FILE  done    Compute the canonicalized name by finding the physical path    for the directory we re in and appending the target file  PHYS DIR  pwd -P  RESULT  PHYS DIR  TARGET FILE echo  RESULT   Note that this doesn t include any error handling   Of particular importance  it doesn t detect symlink cycles   A simple way to do this would be to count the number of times you go around the loop and fail if you hit an improbably large number  such as 1 000   EDITED to use pwd -P instead of  PWD   Note that this script expects to be called like   script name filename  no -f  change  1 to  2 if you want to be able to use with -f filename like GNU readlink

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Install homebrew Run  brew install coreutils  Run  greadlink -f path    greadlink is the gnu readlink that implements -f  You can use macports or others as well  I prefer homebrew

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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           amp  amp  echo -e  ERROR  readlink  lt link to analyze gt   1 gt  amp 2  amp  amp  exit 99  link   1  while   -L   link     do   lastLink   link    link    bin ls -ldq   link     link    link    - gt       link   realpath   link         link       lastlink     amp  amp  echo -e  ERROR  link loop detected on  link  1 gt  amp 2  amp  amp  break done  echo   link

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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

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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

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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 -       amp  amp  target   target      cd -P   2 gt  dev null    return 1   while     max symlinks  -ge 0    amp  amp  max symlinks    max symlinks - 1    do     if       target       target         then       case  target in             cd -P    target       2 gt  dev null    break               cd -P      target      2 gt  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 - gt   s n            lt file mode gt    lt number of links gt    lt owner name gt    lt group name gt            lt size gt    lt date and time gt    lt pathname of link gt    lt contents of link gt        https   pubs opengroup org onlinepubs 9699919799 utilities ls html     link   ls -dl --   target  2 gt  dev null     break     target   link     target - gt       done   return 1     Please refer to the latest code  It may some fixed

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Implementation  Install brew  Follow the instructions at https   brew sh   Install the coreutils package  brew install coreutils  Create an Alias  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   quot Core Utilities quot   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

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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

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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

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What about this   function readlink       DIR    1         cd   DIR   amp  amp  echo    pwd -P

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The paths to readlink are different between my system and yours   Please try specifying the full path       sw sbin readlink -f

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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 - gt   var service clockspeed-adjust lrwxr-xr-x  1 root wheel 29 Dec 13 2013 clockspeed-speed - gt   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

[macos] How can I get the behavior of GNU's readlink -f on a Mac?

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