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Re: Should this be this way?


From: Pierre Gaston
Subject: Re: Should this be this way?
Date: Tue, 26 Feb 2013 14:26:47 +0200

On Tue, Feb 26, 2013 at 11:22 AM, Roman Rakus <address@hidden> wrote:
> On 02/26/2013 02:03 AM, Linda Walsh wrote:
>>
>> My login shell is /bin/bash (i.e. not /bin/sh); SHELL=/bin/bash as well.
>> Typing 'which bash' gives /bin/bash, and whence bash: bash is /bin/bash.
>
> which is not always correct. Use type builtin.
>
>>
>> I had the foll0wing script which acts differently based on
>> whether or not it has a #!/bin/bash at the top: (i.e., as it is
>> displayed below, it fails; one need remove the [] from the first
>> line for it to work.
>> ================
>> #[!/bin/bash]
>
> I think the line above will produce unspecified behavior.

I think the kernel will try to find a shebang and not recognize it,
then the current shell will try to run it

Man bash says:
If  this  execution  fails because the file is not in executable
format, and the file is not a directory, it is assumed to be a shell
script, a file containing shell commands.  A subshell is spawned to
execute it.  This subshell reinitializes itself, so that the effect is
as  if  a  new  shell  had  been  invoked  to  handle  the script,
with the exception that the locations of commands remembered by the
parent (see hash below under SHELL BUILTIN COMMANDS) are retained by
the child.

SUS says

If the execve() function fails due to an error equivalent to the
[ENOEXEC] error defined in the System Interfaces volume of
POSIX.1-2008, the shell shall execute a command equivalent to having a
shell invoked with the pathname resulting from the search as its first
operand, with any remaining arguments passed to the new shell, except
that the value of "$0" in the new shell may be set to the command
name. If the executable file is not a text file, the shell may bypass
this command execution. In this case, it shall write an error message,
and shall return an exit status of 126.



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