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Full Discussion: Scripts without shebang
Top Forums Shell Programming and Scripting Scripts without shebang Post 302694715 by alister on Friday 31st of August 2012 10:24:34 AM
Old 08-31-2012
Quote:
Originally Posted by CarloM
Note that if the script is sourced (e.g. . /path/to/script.sh) rather than run as an executable file then it will be run in the current shell.
True.

With regard to the original post, if the script is sourced, even if the shebang is present, it is never used.

Regards,
Alister

---------- Post updated at 10:02 AM ---------- Previous update was at 09:39 AM ----------

Quote:
Originally Posted by 244an
Is that correct?
I'm on FreeBSD...
It should be correct. It's a fundamental and standardized behavior. From your description, it sounds like you are explicitly passing the script to different shells, but I can't be certain. You did not clearly and unambiguously state the exact commands that you used to create your script and run it. Please do so.

For version info, you should be able to get it from uname -a.

Regards,
Alister

---------- Post updated at 10:24 AM ---------- Previous update was at 10:02 AM ----------

The following excerpts are from the current version of FreeBSD's libc. The most relevant bits have been highlighted:

From FreeBSD CVS - src/lib/libc/gen/exec.c
Code:
retry:		(void)_execve(bp, argv, envp);
		switch (errno) {
		case E2BIG:
			goto done;
		case ELOOP:
		case ENAMETOOLONG:
		case ENOENT:
			break;
		case ENOEXEC:
			for (cnt = 0; argv[cnt]; ++cnt)
				;
			memp = alloca((cnt + 2) * sizeof(char *));
			if (memp == NULL) {
				/* errno = ENOMEM; XXX override ENOEXEC? */
				goto done;
			}
			memp[0] = "sh";
			memp[1] = bp;
			bcopy(argv + 1, memp + 2, cnt * sizeof(char *));
 			(void)_execve(_PATH_BSHELL,
			    __DECONST(char **, memp), envp);
			goto done;

execvpe(3) calls execve(2) (through a libc wrapper). If the system call fails with ENOEXEC, that means that an executable file was found but its format is not recognized. This happens if the file is a foreign binary or if it's a shell script without a shebang. execvpe(3) then reattempts to execve a bourne shell with the unrecognized file as its first argument.

From FreeBSD CVS - src/include/paths.h
Code:
#define	_PATH_BSHELL	"/bin/sh"

The path to the bourne shell is hardcoded in a macro.

I also took a look at glibc and they too share the same implementation design. execlp and execvp wrap execvpe. execvpe takes care of checking errno after execve, retrying with /bin/sh if appropriate. They both use _PATH_BSHELL to point to /bin/sh.

For glibc, the relevant files:
sourceware.org Git - glibc.git/blob - posix/execvpe.c
sourceware.org Git - glibc.git/blob - sysdeps/unix/sysv/linux/paths.h

Regards,
Alister
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