robertd@ncoast.UUCP (Rob DeMarco) (06/11/87)
Can some one tell me in a clear, consise way how bexec differs from exec? Thanks, [> Rd -- [=====================================] [ Rob DeMarco ] [ UUCP:decvax!cwruecmp!ncoast!robertd ] [ ] [ "I hate 'Wheel of fortune'....and ] [ proud of it!!" ] [=====================================]
allbery@ncoast.UUCP (Brandon Allbery) (06/13/87)
Since there's been some discussion on the net about the situation that "bexec"
was designed to solve, I feel justified in posting this to the whole world
instead of mailing it.
As quoted from <2625@ncoast.UUCP> by robertd@ncoast.UUCP (Rob DeMarco):
+---------------
| Can some one tell me in a clear, consise way how bexec differs from exec?
+---------------
The program bexec has very little relation to the exec system call or the
exec shell command which uses the exec system call. It is intended to fix
a "feature" of csh which is now widely considered a bug; it also adds features
to older versions of csh.
Some (all?) versions of csh have the ability to pass non-a.out files (shell
scripts or other non-machine-code files) to a user-specified program; the
feature is enabled by aliasing "shell" to the full pathname of the program.
All versions of csh will, if the "alias shell" feature is not used, check
the first character of a script for being "#" and, if it is, run it as a
csh script; otherwise running it as a sh script.
The original version of bexec simply forced all scripts to be run by sh.
Soon after I wrote it, I changed it to check the first line for #! and do
the appropriate thing. It didn't do setuid, but it tried to do the rest.
(Robert, this is the version ncoast runs.)
Unfortunately, this version didn't do it right. (It passed the script as
standard input, not as an argument.) So, I wrote another version. This one
handles #! correctly; it also checks to see if the first block of the file
contains any non-ASCII characters (octal \200-\377) and if so, sets the
RUNPATH environment variable to the program's full pathname and invokes
RM/COBOL (runcobol) on it; the effect being that RM/COBOL executables may
be run directly.
I have no idea if 4.[123]BSD still supports "alias shell", for the run /bin/sh
and runcobol features (the kernel handles #! so you get the kernel one rather
than the bexec one); but if it does, BSDers may be interested in it. (Of
course, it might be difficult to find RM/COBOL for BSD....) It is, however,
almost a must for sites running SysIII or SysV which has an add-on "old" csh,
since it adds all of these features.
If anyone's interested, send mail and I'll post it.
++Brandon
--
Copyright (C) 1987 Brandon S. Allbery. Redistribution permitted only if the
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