If I want to execute a bash script which doesn't have its execution permission set, I can do:

bash script.sh

What should I use instead of bash if the script isn't executable and I don't know the correct interpreter? Is there a command that looks up the interpreter from shebang line and executes the script with it?

  • What's wrong wit bash?
    – steffen
    Nov 19, 2016 at 7:06
  • @steffen how do you know the file in question is a bash script?
    – muru
    Nov 19, 2016 at 10:07
  • @muru quote from Question: "If I want to execute a bash script..." Moreover (even if it is not a bash script), if bash whatever works, why use something different? bash is available on virtually every *ix system, so why bother...
    – steffen
    Nov 19, 2016 at 12:05
  • 2
    @steffen did you read the rest of the question? They say: "If ... then I can do: ..." and "What should I use instead of bash if ... I don't know the correct interpreter?"
    – muru
    Nov 19, 2016 at 12:07
  • @muru: maybe I don't see the obvious. But if the file /has/ a shebang line, as stated in the question, bash will do exactly what is asked for. As will perl, according to the answer below. So what is the advantage of not using bash?
    – steffen
    Nov 21, 2016 at 20:02

3 Answers 3


Yep. It is called perl. Some examples, with the corresponding interpreter in the shebang line of the file (the actual file extension doesn't matter):

perl foo.bash    # works
perl foo.lua     # works
perl foo.clisp   # works
perl foo.csh     # works
perl foo.php     # works
perl foo.gnuplot # works (no arguments)
perl foo.pl      # works (obviously)
perl foo.py      # works
perl foo.sh      # works
perl foo.tcl     # works
perl foo.rb      # works
perl foo.nodejs  # works
perl foo.r       # works
perl foo.oct     # works
perl foo.csharp  # works (no arguments)

This is mentioned in Perl's documentation:

If the #! line does not contain the word "perl" nor the word "indir", the program named after the #! is executed instead of the Perl interpreter. This is slightly bizarre, but it helps people on machines that don't do #! , because they can tell a program that their SHELL is /usr/bin/perl, and Perl will then dispatch the program to the correct interpreter for them.

  • 47
    Well, that's just dirty.
    – slim
    Nov 17, 2016 at 19:47
  • 1
    Does the file extension .js also work?
    – Pysis
    Nov 18, 2016 at 19:08
  • 1
    Also, what machines don't do #!. I've seem a few to more now, and have not experienced this problem.
    – Pysis
    Nov 18, 2016 at 19:08
  • 1
    Ok, it's just your example seemed to highlight a lot of file extensions, rather than showcase several shebang lines from files, and I guess I assumed that's how its prediction worked.
    – Pysis
    Nov 19, 2016 at 3:06
  • 4
    I like how man perlrun sheepishly admits that it's "slightly bizarre" :). I think this should be treated as a curiosity aimed at non-UNIX environments and very very old versions of UNIX.
    – slim
    Nov 19, 2016 at 17:31

Scripts do not necessarily have a shebang

If the script was run from the interpreter, You cannot be sure it has the shebang at all. Scripts, run from the interpreter do not need the shebang, if you call the interpreter to run the code.

The answer is therefore no, there is no command that will find out for sure what is the language (interpreter) to run the script with. You can however always look inside the script and see if it has the shebang to find out.

The rules in short:

  1. When you run the script, calling the interpreter always overrules possible shebangs, executable or not, shebang or not.
  2. If not executable and run from the interpreter, the script needs no shebang.
  3. If the script is run without calling the interpreter first, it needs (and uses) the shebang to find out what interpreter to call, and it needs to be executable to have the "permission" to call the interpreter from its shebang.

If the script has no shebang however, there is no (direct*) information inside the script to tell what interpreter to use.

Having said that

You could of course always write a wrapper script to try to find out if the script has the shebang and read the interpreter from that, subsequently run it from the found interpreter.

An example

#!/usr/bin/env python3
import subprocess
import sys

args = sys.argv[1:]; script = args[0]

    lang = open(script).readlines()[0].replace("#!", "").strip().split()[-1]
    cmd = [lang, script]+args[1:]
except (PermissionError, FileNotFoundError, IndexError):
    print("No valid shebang found")
  • Save it as tryrun in $PATH (e.g. ~/bin, make the directory if it does not exist, log out and back in), make it executable. Then running:

    tryrun /path/to/nonexecutablescript

    calls (tested) the correct interpreter on my non-executable python and bash scripts.


  • The script simply reads the first line of the script, removes the #! and uses the rest to call the interpreter.
  • If it fails to call a valid interpreter, it will raise either a PermissionError or a FileNotFoundError.


The extension (.sh, .py etc) plays no role whatsoever in determining the appropriate interpreter on Linux.

(*It is of course possible to develop a "smart" guess- algorithm to determine the syntax from the code.)

  • OK, so it means although Linux has shebang extraction implemented somewhere (so that it can select correct interpreter for executable srcipts), it's not provided as a standalone standard command.
    – Aivar
    Nov 17, 2016 at 12:01
  • @Aivar extracting the shebang isn' t the issue, but running code without it is perfectly possible. Nov 17, 2016 at 13:46
  • @Aivar Ah, I see what you mean. If the script is executable and run without language in the command, the script calls the interpreter, not the other way around. Nov 17, 2016 at 13:55
  • 1
    @JacobVlijm I wouldn't say "the script calls the interpreter", more like "the Linux kernel takes the shebang line for figuring out which interpreter to call when executing the script". Nov 17, 2016 at 20:37
  • @PaŭloEbermann Thanks! True of course. The kernel takes care of the whole procedure either way, but figuratively, and I think better for understanding, is to say the script is "allowed" to take care of what interpreter to call (and actually do it). Not sure about the wording, but I' d like to describe it as if the initiative is on the script, while the kernel actually does the job. Nov 17, 2016 at 20:47

You can achieve this with a script like this:


cp $1 ${copy}
chmod u+x ${copy}
rm ${copy}


$ echo "echo hello" > myscript
$ ./myscript
bash: ./myscript: Permission denied
$ ./runscript myscript 

I recommend against doing this. Permissions are there for a reason. This is a program for subverting permissions.

Note that shebang handling is a kernel function (in the Linux source code - fs/binfmt_script.c). Fundamentally the process invoking a script directly doesn't know about the #! -- the kernel uses it to work out that it needs to launch an interpreter.

  • 2
    I had always assumed that was a function of the shell, NOT the kernel. Learned something new today.
    – boatcoder
    Nov 18, 2016 at 20:54
  • 1
    @boatcoder -- Since you're interested, added a link to where the Linux source code handles it.
    – slim
    Nov 19, 2016 at 16:50

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