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From: Brandon Allbery <
[email protected]>
Newsgroups: net.unix-wizards,net.sources
Subject: csh vs. # comments in bourne shell scripts
Message-ID: <
[email protected]>
Date: 10 Dec 85 03:08:18 GMT
Followup-To: net.unix-wizards
Xref: seismo net.unix-wizards:16109 net.sources:4009
To:
[email protected]
Expires:
Quoted from <
[email protected]> ["Re: Magic Numbers"], by
[email protected] (Doug Gwyn <gwyn>)...
+---------------
| > Csh on non-4.2 systems checks for a # as
| > the first character of the file, and forks itself if it sees it; if not, it
| > forks a /bin/sh.
|
| Yes, some of them do, but if they do that's a bug.
| Virtually all of my Bourne shell scripts (including
| SVR2 system utility scripts) start with "#".
+---------------
All of them do. When csh was written bsh still only spoke :.
There *is* a simple (albeit slow) solution. Write a program to intuit the
program to invoke on the file, with the file's full pathname passed as argv[1]
and its arguments as argv[2] .. argv[argc - 1]. Then say:
alias shell $HOME/bin/bexec
or whatever you decide to call it. IT MUST BE A BINARY FILE AND IT MUST BE A
FULL PATHNAME. If csh can't exec() a program it will prepend the value of the
``shell'' alias to it, if any, and try again; if there isn't a shell alias it
uses its own heuristics.
The program below uses this (mis-?)feature of bastard (orphaned?) csh'es to
handle #! magic numbers, sans set[ug]id and other fun stuff. Other than
that it uses the same test as csh itself. But you can do whatever you like,
say to use * to cause your local Kermit-running MS-DOS machine to receive and
execute the file as an MS-DOS batch file. [ :-) ] Let me know if you come
up with any interesting new twists.
--Brandon
----------------------------- cut here ---------------------------------------
#include <stdio.h>
#include <fcntl.h>
/*
* bexec: execute a non-binary file for csh, with #! recognition
* (usage: alias shell /usr/local/bin/bexec)
*/
extern int errno;
extern char *sys_errlist[];
#define SH "/bin/sh"
#define CSH "/usr/plx/csh"
#define NARG 512 /* this is the number csh uses */
char *sysargv[NARG + 1];
char **newargv();
char *basename();
extern char *strrchr();
main(argc, argv, envp)
char **argv, **envp; {
FILE *cmd;
char kcmd[512];
char *cp, *ap;
if ((cmd = fopen(argv[1], "r")) == NULL) {
fprintf(stderr, "bexec: can't open %s: %s\n", argv[1], sys_errlist[errno]);
exit(1);
}
fgets(kcmd, sizeof kcmd, cmd);
kcmd[strlen(kcmd) - 1] = '\0'; /* kill trailing \n */
if (strncmp(kcmd, "#!", 2) != 0) {
if (kcmd[0] == '#') {
argv[0] = "csh";
cp = CSH;
}
else {
argv[0] = "sh";
cp = SH;
}
execve(cp, argv, envp);
fprintf(stderr, "bexec: can't exec %s: %s\n", cp, sys_errlist[errno]);
exit(100);
}
for (cp = kcmd + 2; *cp == ' '; cp++)
;
for (ap = cp; *ap != ' ' && *ap != '\0'; ap++)
;
if (*ap == ' ')
*ap++ = '\0';
argv = newargv(basename(argv[1]), ap, argv);
fclose(stdin);
fcntl(fileno(cmd), F_DUPFD, 0);
lseek(0, ftell(cmd), 0);
fclose(cmd);
execve(cp, argv, envp);
fprintf(stderr, "bexec: can't exec %s: %s\n", cp, sys_errlist[errno]);
exit(100);
}
char **newargv(newar0, newar1, oldargv)
char *newar0, *newar1, **oldargv; {
int ap, op;
sysargv[0] = newar0;
ap = 1;
if (newar1[0] != '\0') {
sysargv[1] = newar1;
ap++;
}
for (op = 2; ap < NARG && oldargv[op] != NULL; ap++, op++)
sysargv[ap] = oldargv[op];
sysargv[ap] = NULL;
return sysargv;
}
char *basename(path)
char *path; {
char *cp;
if ((cp = strrchr(path, '/')) == NULL)
return path;
return cp + 1;
}
--
Lord Charteris (thurb)
[email protected] (ncoast!allbery%
[email protected])
.decvax!cwruecmp!ncoast!allbery (..ncoast!tdi2!root for business)
6615 Center St., Mentor, OH 44060 (I moved) --Phone: +01 216 974 9210
CIS 74106,1032 -- MCI MAIL BALLBERY (WARNING: I am only a part-time denizen...)
