Check if a file is executable

Question

I am wondering what s the easiest way to check if a program is executable  with bash  without executing it   It should at least check whether the file has execute rights  and is of the same architecture  for example  not a windows executable or another unsupported architecture  not 64 bits if the system is 32 bits       as the current system

User · Answer

First you need to remember that in Unix and Linux, everything is a file, even directories. For a file to have the rights to be executed as a command, it needs to satisfy 3 conditions:

It needs to be a regular file
It needs to have read-permissions
It needs to have execute-permissions

So this can be done simply with:

[ -f "${file}" ] && [ -r "${file}" ] && [ -x "${file}" ]

If your file is a symbolic link to a regular file, the test command will operate on the target and not the link-name. So the above command distinguishes if a file can be used as a command or not. So there is no need to pass the file first to realpath or readlink or any of those variants.

If the file can be executed on the current OS, that is a different question. Some answers above already pointed to some possibilities for that, so there is no need to repeat it here.

User · Answer

Also seems nobody noticed -x operator on symlinks   A symlink  chain  to a regular file  not classified as executable  fails the test

User · Answer

Seems nobody noticed that -x operator does not differ file with directory   So to precisely check an executable file  you may use      -f SomeFile  amp  amp  -x SomeFile

User · Answer

To  test whether a  file itself has ACL EXECUTE bit set in  any of  permission sets  user  group  others  regardless of  where it resides  i   e  even on  a  tmpfs with  noexec option  use stat -c   A  to  get the  permission string and  then check if it contains at  least a  single    x    letter     if       stat -c   A   my exec file         x        then     echo  Has executable permission for someone  fi   The  right-hand part of  comparison may be modified to  fit more specific cases  such  as  x x x  to  check whether all kinds of  users should be able to  execute the  file when it is placed on  a  volume mounted with  exec option

User · Answer

This might be not so obvious  but sometime is required to test the executable to appropriately call it without an external shell process   function tkl is file os exec            -x   1      amp  amp  return 255    local exec header bytes   case   OSTYPE  in     cygwin    msys    mingw           CAUTION            The bash version 3 2  might require a file path together with the extension            otherwise will throw the error   bash       No such file or directory             So we make a guess to avoid the error                          read -r -n 4 exec header bytes 2 gt   dev null  lt    1                            -x    1  exe  exe      amp  amp  read -r -n 4 exec header bytes 2 gt   dev null  lt     1  exe  exe                                      -x    1  com  com      amp  amp  read -r -n 4 exec header bytes 2 gt   dev null  lt     1  com  com                     amp  amp        if       exec header bytes 0 3        MZ x90      then             MZ x90 00  for bash version 3 2 42              MZ x90 03  for bash version 4 0                exec header bytes 3 1         x00        exec header bytes 3 1         x03      amp  amp  return 0       fi                     read -r -n 4 exec header bytes  lt    1             exec header bytes        x7fELF      amp  amp  return 0          esac    return 1      executes script in the shell process in case of a shell script  otherwise executes as usual function tkl exec inproc       if tkl is file os exec   1   then            else              fi   return        myscript sh      bin bash  echo 123  return 123   In Cygwin    gt  tkl exec inproc  cygdrive c Windows system32 cmd exe  c  echo 123  123  gt  tkl exec inproc  cygdrive c Windows system32 chcp com 65001 Active code page  65001  gt  tkl exec inproc   myscript sh 123  gt  echo    123   In Linux    gt  tkl exec inproc  bin bash -c  echo 123  123  gt  tkl exec inproc   myscript sh 123  gt  echo    123

User · Answer

Testing files  directories and symlinks The solutions given here fail on either directories or symlinks  or both   On Linux  you can test files  directories and symlinks with  if    -f  quot  file quot   amp  amp  -x   realpath  quot  file quot       then      fi  On OS X  you should be able to install coreutils with homebrew and use grealpath  Defining an isexec function You can define a function for convenience  isexec         if    -f  quot  1 quot   amp  amp  -x   realpath  quot  1 quot       then         true      else         false      fi     Or simply isexec        -f  quot  1 quot   amp  amp  -x   realpath  quot  1 quot          Then you can test using  if  isexec  quot  file quot    then     fi

User · Answer

Take a look at the various test operators  this is for the test command itself  but the built-in BASH and TCSH tests are more or less the same    You ll notice that -x FILE says FILE exists and execute  or search  permission is granted   BASH  Bourne  Ksh  Zsh Script  if    -x   file     then     echo  File   file  is executable  else     echo  File   file  is not executable or found  fi   TCSH or CSH Script   if   -x   file    then     echo  File   file  is executable  else     echo  File   file  is not executable or found  endif   To determine the type of file it is  try the file command  You can parse the output to see exactly what type of file it is  Word  o Warning  Sometimes file will return more than one line  Here s what happens on my Mac     file  bin ls      bin ls  Mach-O universal binary with 2 architectures  bin ls  for architecture x86 64    Mach-O 64-bit executable x86 64  bin ls  for architecture i386      Mach-O executable i386   The file command returns different output depending upon the OS  However  the word executable will be in executable programs  and usually the architecture will appear too   Compare the above to what I get on my Linux box     file  bin ls  bin ls  ELF 64-bit LSB executable  AMD x86-64  version 1  SYSV   for GNU Linux 2 6 9  dynamically linked  uses shared libs   stripped   And a Solaris box     file  bin ls  bin ls         ELF 32-bit MSB executable SPARC Version 1  dynamically linked  stripped   In all three  you ll see the word executable and the architecture  x86-64  i386  or SPARC with 32-bit       Addendum     Thank you very much  that seems the way to go  Before I mark this as my answer  can you please guide me as to what kind of script shell check I would have to perform  ie  what kind of parsing  on  file  in order to check whether I can execute a program   If such a test is too difficult to make on a general basis  I would at least like to check whether it s a linux executable or osX  Mach-O    Off the top of my head  you could do something like this in BASH   if   -x   file     amp  amp  file   file    grep -q  Mach-O  then     echo  This is an executable Mac file  elif   -x   file     amp  amp  file   file    grep -q  GNU Linux  then     echo  This is an executable Linux File  elif   -x   file     amp  amp  file   file    grep q  shell script  then     echo  This is an executable Shell Script  elif   -x   file    then     echo  This file is merely marked executable  but what type is a mystery  else     echo  This file isn t even marked as being executable  fi   Basically  I m running the test  then if that is successful  I do a grep on the output of the file command  The grep -q means don t print any output  but use the exit code of grep to see if I found the string  If your system doesn t take grep -q  you can try grep  regex   gt   dev null 2 gt  amp 1   Again  the output of the file command may vary from system to system  so you ll have to verify that these will work on your system  Also  I m checking the executable bit  If a file is a binary executable  but the executable bit isn t on  I ll say it s not executable  This may not be what you want

[bash] Check if a file is executable

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