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 · Accepted 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 "$file" ] && file "$file" | grep -q "Mach-O"
then
    echo "This is an executable Mac file"
elif [ -x "$file" ] && file "$file" | grep -q "GNU/Linux"
then
    echo "This is an executable Linux File"
elif [ -x "$file" ] && file "$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" > /dev/null 2>&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.

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  quot   file  quot     amp  amp    -r  quot   file  quot     amp  amp    -x  quot   file  quot     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

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

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

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

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

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

[bash] Check if a file is executable

Addendum

Examples related to bash

Examples related to tcsh