How to resolve symbolic links in a shell script

Question

Given an absolute or relative path  in a Unix-like system   I would like to determine the full path of the target after resolving any intermediate symlinks  Bonus points for also resolving  username notation at the same time   If the target is a directory  it might be possible to chdir   into the directory and then call getcwd    but I really want to do this from a shell script rather than writing a C helper  Unfortunately  shells have a tendency to try to hide the existence of symlinks from the user  this is bash on OS X      ls -ld foo bar drwxr-xr-x   2 greg  greg  68 Aug 11 22 36 bar lrwxr-xr-x   1 greg  greg   3 Aug 11 22 36 foo - gt  bar   cd foo   pwd  Users greg tmp foo     What I want is a function resolve   such that when executed from the tmp directory in the above example  resolve  foo        Users greg tmp bar

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Putting some of the given solutions together  knowing that readlink is available on most systems  but needs different arguments  this works well for me on OSX and Debian  I m not sure about BSD systems  Maybe the condition needs to be     OSTYPE    darwin     to exclude -f from OSX only      bin bash MY DIR    cd   dirname   readlink      OSTYPE    linux      amp  amp  echo  -f    0     pwd -P  echo   MY DIR

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Since I ve run into this many times over the years  and this time around I needed a pure bash portable version that I could use on OSX and linux  I went ahead and wrote one   The living version lives here   https   github com keen99 shell-functions tree master resolve path  but for the sake of SO  here s the current version  I feel it s well tested  but I m open to feedback    Might not be difficult to make it work for plain bourne shell  sh   but I didn t try   I like  FUNCNAME too much         bin bash  resolve path          I m bash only  please        usage   resolve path  lt a file or directory gt         follows symlinks and relative paths  returns a full real path           local owd   PWD       echo   FUNCNAME for  1   gt  amp 2     local opath   1      local npath        local obase   basename   opath       local odir   dirname   opath       if    -L   opath         then      it s a link       file or directory  we want to cd into it s dir         cd  odir      then extract where the link points          npath   readlink   obase            have to -L BEFORE we -f  because -f includes -L            if    -L  npath             then          the link points to another symlink  so go follow that              resolve path   npath               and finish out early  we re done              return                 done         elif    -f  npath             the link points to a file           then              get the dir for the new file             nbase   basename  npath              npath   dirname  npath              cd   npath              ndir   pwd -P              retval 0              done         elif    -d  npath             then          the link points to a directory              cd   npath              ndir   pwd -P              retval 0              done         else             echo   FUNCNAME  ERROR  unknown condition inside link     gt  amp 2             echo  opath     opath      gt  amp 2             echo  npath     npath      gt  amp 2             return 1         fi     else         if      -e   opath              then             echo   FUNCNAME   opath  No such file or directory   gt  amp 2             return 1              and break early         elif    -d   opath              then              cd   opath              ndir   pwd -P              retval 0              done         elif    -f   opath              then             cd  odir             ndir   pwd -P              nbase   basename   opath               retval 0              done         else             echo   FUNCNAME  ERROR  unknown condition outside link     gt  amp 2             echo  opath     opath      gt  amp 2             return 1         fi     fi      now assemble our output     echo -n   ndir      if     x  nbase         x          then         echo    nbase      else          echo     fi      now return to where we were     cd   owd      return  retval     here s a classic example  thanks to brew      ls -l  which mvn  lrwxr-xr-x  1 draistrick  502  29 Dec 17 10 50  usr local bin mvn  - gt     Cellar maven 3 2 3 bin mvn   use this function and it will return the -real- path      cat test sh    bin bash   resolve path inc echo echo  relative symlinked path   which mvn echo echo  and the real path   resolve path  which mvn       test sh  relative symlinked path   usr local bin mvn  and the real path   usr local Cellar maven 3 2 3 libexec bin mvn

User · Answer

My answer here Bash  how to get real path of a symlink   but in short very handy in scripts   script home    dirname   realpath   0     echo Original script home   script home   These are part of GNU coreutils  suitable for use in Linux systems   To test everything  we put symlink into  home test2   amend some additional things and run call it from root directory       home test2 symlink  home test Original script home   home test   Where   Original script is   home test realscript sh Called script is   home test2 symlink

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Common shell scripts often have to find their  home  directory even if they are invoked as a symlink  The script thus have to find their  real  position from just  0   cat  mvn    on my system prints a script containing the following  which should be a good hint at what you need   if   -z   M2 HOME      then      resolve links -  0 may be a link to maven s home   PRG   0       need this for relative symlinks   while   -h   PRG      do     ls  ls -ld   PRG       link  expr   ls       - gt                if expr   link           gt   dev null  then       PRG   link      else       PRG   dirname   PRG    link      fi   done    saveddir  pwd     M2 HOME  dirname   PRG           make it fully qualified   M2 HOME  cd   M2 HOME   amp  amp  pwd

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Here s how one can get the actual path to the file in MacOS Unix using an inline Perl script   FILE   perl -e  use Cwd qw abs path   print abs path   0       Similarly  to get the directory of a symlinked file   DIR   perl -e  use Cwd qw abs path   use File  Basename  print dirname abs path   0

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Try this   cd   dirname     -L  0    amp  amp  readlink -f  0    echo  0

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readlink -f   path    Editor s note  The above works with GNU readlink and FreeBSD PC-BSD OpenBSD readlink  but not on OS X as of 10 11  GNU readlink offers additional  related options  such as -m for resolving a symlink whether or not the ultimate target exists   Note since GNU coreutils 8 15  2012-01-06   there is a realpath program available that is less obtuse and more flexible than the above  It s also compatible with the FreeBSD util of the same name  It also includes functionality to generate a relative path between two files   realpath  path      Admin addition below from comment by halloleo    danorton    For Mac OS X  through at least 10 11 x   use readlink without the -f option   readlink  path   Editor s note  This will not resolve symlinks recursively and thus won t report the ultimate target  e g   given symlink a that points to b  which in turn points to c  this will only report b  and won t ensure that it is output as an absolute path   Use the following perl command on OS X to fill the gap of the missing readlink -f functionality  perl -MCwd -le  print Cwd  abs path shift     path

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Is your path a directory  or might it be a file  If it s a directory  it s simple    cd   DIR   pwd -P    However  if it might be a file  then this won t work   DIR   cd   dirname   FILE    pwd -P   echo    DIR    readlink   FILE      because the symlink might resolve into a relative or full path   On scripts I need to find the real path  so that I might reference configuration or other scripts installed together with it  I use this   SOURCE    BASH SOURCE 0    while   -h   SOURCE     do   resolve  SOURCE until the file is no longer a symlink   DIR     cd -P     dirname   SOURCE      amp  amp  pwd      SOURCE    readlink   SOURCE          SOURCE           amp  amp  SOURCE   DIR  SOURCE    if  SOURCE was a relative symlink  we need to resolve it relative to the path where the symlink file was located done   You could set SOURCE to any file path  Basically  for as long as the path is a symlink  it resolves that symlink  The trick is in the last line of the loop  If the resolved symlink is absolute  it will use that as SOURCE  However  if it is relative  it will prepend the DIR for it  which was resolved into a real location by the simple trick I first described

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function realpath       local r  1  local t   readlink  r      while    t    do         r   cd   dirname  r   amp  amp  cd   dirname  t   amp  amp  pwd -P    basename  t          t   readlink  r      done     echo  r     example usage SCRIPT PARENT DIR   dirname   realpath   0

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Another way     Gets the real path of a link  following all links myreadlink         -h   1     amp  amp  echo   1      local link    expr    command ls -ld --   1         - gt              cd   dirname  1   myreadlink   link    sed  s                 dirname  1   1          Returns the absolute path to a command  maybe in  PATH  which  or not  If not found  returns the same whereis     echo  1   sed  s                  pwd   1  s               which --  1   s     1          Returns the realpath of a called command  whereis realpath     local SCRIPT PATH   whereis  1   myreadlink   SCRIPT PATH    sed  s                 dirname   SCRIPT PATH    1

User · Answer

pwd -P  seems to work if you just want the directory  but if for some reason you want the name of the actual executable I don t think that helps  Here s my solution      bin bash    get the absolute path of the executable SELF PATH   cd -P --    dirname --   0     amp  amp  pwd -P   amp  amp  SELF PATH  SELF PATH   basename --   0      resolve symlinks while    -h  SELF PATH     do       1  cd to directory of the symlink       2  cd to the directory of where the symlink points       3  get the pwd       4  append the basename     DIR   dirname --   SELF PATH       SYM   readlink   SELF PATH       SELF PATH   cd   DIR   amp  amp  cd    dirname --   SYM     amp  amp  pwd    basename --   SYM   done

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This is a symlink resolver in Bash that works whether the link is a directory or a non-directory   function readlinks      set -o errexit -o nounset   declare n 0 limit 1024 link   1       If it s a directory  just skip all this    if cd   link  2 gt  dev null   then     pwd -P     return 0   fi      Resolve until we are out of links  or recurse too deep     while    -L  link     amp  amp      n -lt  limit      do     cd    dirname --   link        n    n   1       link    readlink --    link           done   cd    dirname --   link       if     n -ge  limit      then     echo  Recursion limit   limit  exceeded    gt  amp 2     return 2   fi    printf   s  s n     pwd -P      link            Note that all the cd and set stuff takes place in a subshell

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One of my favorites is realpath foo   realpath - return the canonicalized absolute pathname  realpath  expands  all  symbolic  links  and resolves references to               and extra     characters in the null terminated string named by path and        stores the canonicalized absolute pathname in the buffer of size PATH MAX named by resolved path   The resulting path will have no symbolic link        or               components

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Note  I believe this to be a solid  portable  ready-made solution  which is invariably lengthy for that very reason   Below is a fully POSIX-compliant script   function that is therefore cross-platform  works on macOS too  whose readlink still doesn t support -f as of 10 12  Sierra   - it uses only POSIX shell language features and only POSIX-compliant utility calls   It is a portable implementation of GNU s readlink -e  the stricter version of readlink -f    You can run the script with sh or source the function in bash  ksh  and zsh   For instance  inside a script you can use it as follows to get the running s script true directory of origin  with symlinks resolved   trueScriptDir   dirname --    rreadlink   0         rreadlink script   function definition   The code was adapted with gratitude from this answer  I ve also created a bash-based stand-alone utility version here  which you can install with npm install rreadlink -g  if you have Node js installed      bin sh    SYNOPSIS     rreadlink  lt fileOrDirPath gt    DESCRIPTION     Resolves  lt fileOrDirPath gt  to its ultimate target  if it is a symlink  and     prints its canonical path  If it is not a symlink  its own canonical path     is printed      A broken symlink causes an error that reports the non-existent target    LIMITATIONS     - Won t work with filenames with embedded newlines or filenames containing        the string   - gt       COMPATIBILITY     This is a fully POSIX-compliant implementation of what GNU readlink s      -e option does    EXAMPLE     In a shell script  use the following to get that script s true directory of origin        trueScriptDir   dirname --    rreadlink   0     rreadlink       Execute the function in a  subshell  to localize variables and the effect of  cd      target  1 fname  targetDir  CDPATH       Try to make the execution environment as predictable as possible      All commands below are invoked via  command   so we must make sure that      command  itself is not redefined as an alias or shell function       Note that command is too inconsistent across shells  so we don t use it        command  is a  builtin  in bash  dash  ksh  zsh  and some platforms do not      even have an external utility version of it  e g  Ubuntu        command  bypasses aliases and shell functions and also finds builtins      in bash  dash  and ksh  In zsh  option POSIX BUILTINS must be turned on for     that to happen       unalias command   unset -f command     gt  dev null 2 gt  amp 1     -n   ZSH VERSION     amp  amp  options POSIX BUILTINS  on   make zsh find  builtins  with  command  too     while    do   Resolve potential symlinks until the ultimate target is found          -L   target         -e   target         command printf   s n   ERROR    target  does not exist    gt  amp 2  return 1          command cd    command dirname --   target      Change to target dir  necessary for correct resolution of target path        fname   command basename --   target     Extract filename            fname           amp  amp  fname         curiously   basename    returns           if   -L   fname     then           Extract  next  target path  which may be defined            relative  to the symlink s own directory            Note  We parse  ls -l  output to find the symlink target                 which is the only POSIX-compliant  albeit somewhat fragile  way          target   command ls -l   fname           target   target   - gt            continue   Resolve  next  symlink target        fi       break   Ultimate target reached    done   targetDir   command pwd -P    Get canonical dir  path     Output the ultimate target s canonical path      Note that we manually resolve paths ending in    and     to make sure we have a normalized path    if     fname           then     command printf   s n     targetDir       elif      fname            then       Caveat  something like  var    will resolve to  private  assuming  var  - gt   private var   i e  the      is applied       AFTER canonicalization      command printf   s n     command dirname --    targetDir       else     command printf   s n     targetDir     fname    fi    rreadlink          A tangent on security   jarno  in reference to the function ensuring that builtin command is not shadowed by an alias or shell function of the same name  asks in a comment      What if unalias or unset and   are set as aliases or shell functions    The motivation behind rreadlink ensuring that command has its original meaning is to use it to bypass  benign  convenience aliases and functions often used to shadow standard commands in interactive shells  such as redefining ls to include favorite options   I think it s safe to say that unless you re dealing with an untrusted  malicious environment  worrying about unalias or unset - or  for that matter  while  do      - being redefined is not a concern   There is something that the function must rely on to have its original meaning and behavior - there is no way around that  That POSIX-like shells allow redefinition of builtins and even language keywords is inherently a security risk  and writing paranoid code is hard in general    To address your concerns specifically   The function relies on unalias and unset having their original meaning  Having them redefined as shell functions in a manner that alters their behavior would be a problem  redefinition as an alias is not necessarily a concern  because quoting  part of  the command name  e g    unalias  bypasses aliases   However  quoting is not an option for shell keywords  while  for  if  do       and while shell keywords do take precedence over shell functions  in bash and zsh aliases have the highest precedence  so to guard against shell-keyword redefinitions you must run unalias with their names  although in non-interactive bash shells  such as scripts  aliases are not expanded by default - only if shopt -s expand aliases is explicitly called first    To ensure that unalias - as a builtin - has its original meaning  you must use  unset on it first  which requires that unset have its original meaning   unset is a shell builtin  so to ensure that it is invoked as such  you d have to make sure that it itself is not redefined as a function  While you can bypass an alias form with quoting  you cannot bypass a shell-function form - catch 22   Thus  unless you can rely on unset to have its original meaning  from what I can tell  there is no guaranteed way to defend against all malicious redefinitions

User · Answer

readlink -e  filepath    seems to be exactly what you re asking for  - it accepts an arbirary path  resolves all symlinks  and returns the  real  path - and it s  standard  nix  that likely all systems already have

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To work around the Mac incompatibility  I came up with  echo  php -r  echo realpath  foo        Not great but cross OS

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Here I present what I believe to be a cross-platform  Linux and macOS at least  solution to the answer that is working well for me currently   crosspath         local ref   1      if   -x    which realpath      then         path    realpath   ref        else         path    readlink -f   ref  2 gt   dev null           if      -gt 0    then             if   -x    which readlink      then                 if     -z    readlink   ref       then                     ref    readlink   ref                    fi             else                 echo  realpath and readlink not available  The following may not be the final path   1 gt  amp 2             fi             if   -d   ref     then                 path    cd   ref   pwd -P               else                 path    cd   dirname   ref    pwd -P    basename   ref                fi         fi     fi     echo   path      Here is a macOS  only   solution  Possibly better suited to the original question   mac realpath         local ref   1      if      -z    readlink   ref        then         ref    readlink   1        fi     if    -d   ref      then         echo    cd   ref   pwd -P       else         echo    cd   dirname   ref    pwd -P    basename   ref        fi

User · Answer

In case where pwd can t be used  e g  calling a scripts from a different location   use realpath  with or without dirname      dirname   realpath  PATH TO BE RESOLVED     Works both when calling through  multiple  symlink s  or when directly calling the script - from any location

User · Answer

According to the standards  pwd -P should return the path with symlinks resolved   C function char  getcwd char  buf  size t size  from unistd h should have the same behaviour   getcwd pwd

[bash] How to resolve symbolic links in a shell script

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