kjh@visual1.jhuapl.edu (Kenneth J. Heeres) (02/22/91)
If I am writing my own shell command processor and I use the
#! pathname
capability to implicitly invoke it, what happens to the arguments that
were passed to the script???
ken
--
==========================================================================
Kenneth J. Heeres The Johns Hopkins University
INTERNET: kjh@visual1.jhuapl.edu Applied Physics Laboratory
Johns Hopkins Road
Laurel, MD 20723-6099brnstnd@kramden.acf.nyu.edu (Dan Bernstein) (02/22/91)
In article <1991Feb21.172233.8160@aplcen.apl.jhu.edu> kjh@visual1.jhuapl.edu (Kenneth J. Heeres) writes: > If I am writing my own shell command processor and I use the > #! pathname > capability to implicitly invoke it, what happens to the arguments that > were passed to the script??? 1. Your subject line is nearly useless. ``Using #!'' is too general, and ``a different shell'' is irrelevant. Much better would be Subject: With #!pathname, what happens to the args passed to the script? Always put as much information as possible into the subject line. 2. You didn't say what system you're using. For some questions it won't matter---#!, for example, is a BSD feature, and your question has the same answer under any BSD system. Also, anyone on the Internet can use the domain name server or telnet to find out your host type. But your next question may be Ultrix-specific, the name server is unreliable enough with its current load, and a lot of USENET readers aren't on the Internet. Always give at least a minimal description of your environment. 3. Your article is in the wrong group. Do you think that you have enough experience to judge whether a question will catch the interest of any wizards? Probably not. Have you seen the group ``comp.unix.questions''? Why don't you use it if you want to ask a question about UNIX? Always try comp.unix.questions first unless you know your article is more appropriate in another group. 4. There is almost certainly someone at Johns Hopkins who can answer your question. It is easier to mail a question to root or your favorite sysadmin than to post to the net. Always try local resources before bothering thousands of people around the world. 5. You can probably answer the question by experimentation. Presumably you have some program that depends on the behavior you asked about, so why don't you test it for yourself? 6. The answer appears in the execve() man page on every BSD system I've seen. Read the fucking manual. 7. The arguments are placed on the command line after the #!. ---Dan
jik@athena.mit.edu (Jonathan I. Kamens) (02/22/91)
% cat echo-args.c
#include <stdio.h>
main(int argc, char *argv[])
{
if (! argc) {
printf("There are no arguments.\n");
}
else {
printf("The arguments are:");
while (argc--) {
printf(" %s", *argv++);
}
printf("\n");
}
exit(0);
}
% cat use-echo-args
#!/tmp/echo-args
exit 0
% ./use-echo-args foo bar baz
The arguments are: echo-args ./use-echo-args foo bar baz
This is on BSD 4.3; I doubt it's significantly different on other platforms
that allow #!. I guess this is why "#!/bin/awk -f" works.
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Jonathan Kamens USnail:
MIT Project Athena 11 Ashford Terrace
jik@Athena.MIT.EDU Allston, MA 02134
Office: 617-253-8085 Home: 617-782-0710grr@cbmvax.commodore.com (George Robbins) (02/22/91)
In article <1991Feb21.172233.8160@aplcen.apl.jhu.edu> kjh@visual1.jhuapl.edu (Kenneth J. Heeres) writes: > > If I am writing my own shell command processor and I use the > #! pathname > capability to implicitly invoke it, what happens to the arguments that > were passed to the script??? The outline is described in the man entry for execve(). The actual behavior of the Berkeley exec code sets up the arguments as below and leaves stdin assigned to the script at the line folling the #! stuff. first arg: interpreter specified after #! next arg: all arguments specified after above, *not* parsed for delimiters, skipped if no arguments next arg: command from command line next arg: first argument from command line, if any next arg: and so on... The non-parsed arguments from the #! line can be unfortunate since some programs you might wish to use as "interpreters" prefer their arguments parsed. ie "#! awk -f" does what's expected, "#! awk -F: -f" doesn't. In non-hacked AT&T flavors of Unix, the setup is handled by the shell, but the results should be equivalent. -- George Robbins - now working for, uucp: {uunet|pyramid|rutgers}!cbmvax!grr but no way officially representing: domain: grr@cbmvax.commodore.com Commodore, Engineering Department phone: 215-431-9349 (only by moonlite)
guy@auspex.auspex.com (Guy Harris) (02/24/91)
>In non-hacked AT&T flavors of Unix, the setup is handled >by the shell, In non-hacked AT&T flavors of UNIX that don't have "Release 4" in their name, "#!" isn't handled by the kernel nor by the shell. In non-hacked AT&T flavors of UNIX that *do* have "Release 4" in their name, "#!" is handled by the kernel, in the same fashion that it's handled by BSD and by many (probably most, if not all) other systems that have picked up "#!" from BSD.