rcd@ico.isc.com (Dick Dunn) (04/02/91)
Bourne shell users, accustomed to creating or emptying a file with a command like: >splot or rewinding a tape with: </dev/mt0 are occasionally annoyed to find that csh rejects this syntax with the confusing message "Invalid null command". (It is confusing because there is no such thing as a *valid* null command; attempts to find one will only end in frustration.) This can be solved as follows: touch /bin/IEFBR14 chmod 755 IEFBR14 The name is chosen for historical relevance, since most of us who still use the Bourne shell are Luddites or recidivists anyway. Of course, IEFBR14 >splot seems a bit naked without some slashes and an EXEC PGM=, but that's the way these modern systems are... Some folks may note a more-than-coincidental resemblance between this version of IEFBR14 and older versions of /bin/true. So it is, but our example lacks the sophistication of the modern System V "true" command, which is now 9 lines long and includes - an entirely superfluous : - five lines of copyright notice (so don't y'all go trying to use empty files any more; AT&T owns the copyright) - a #ident--which, of course, is meaningless to the shell, but reveals the interesting fact that we're now up to version 2.3 of a formerly-empty file However, the preceding was only for illustration anyway. Nobody wants a dirty old shell script for the null command; it should of course be a C program for efficiency. So here we have the first cut at IEFBR14.c: main() { } This also serves only for illustration; it is historically accurate in that it contains the same bug as IBM's original IEFBR14. (It may be of some interest that IEFBR14 proved the old CS aphorism "Every program contains at least one bug and can be shortened by one instruction" at the inductive limit: It was a single instruction which didn't work...but I digress...) Here's the first correction: main() { exit(0); } But to make this proper in today's brave new world, we need <stdlib.h>. Also, for formality's sake and international propriety, we should add the normally-obligatory setlocale() call (actually not necessary--this may be the *only* program for which that's true--but it's hard to pass up poking fun at a requirement to set a default explicitly), and this in turn requires <locale.h>. OK, so here's the penultimate version of IEFBR14.c, our properly ANSI and internationalized (unless I screwed up) program-to- do-nothing: #include <stdlib.h> #include <locale.h> #ifndef lint static char *sccsid = "%W% - %E%"; #endif /*ARGSUSED*/ main(argc,argv) int argc; char **argv; { setlocale(LC_ALL, ""); exit(0); } To create the final version, all you need is your local draconian corporate screenful of copyright notice and disclaimer. -- Dick Dunn rcd@ico.isc.com -or- ico!rcd Boulder, CO (303)449-2870 The Official Colorado State Vegetable is now the "state legislator".
rbj@uunet.UU.NET (Root Boy Jim) (04/04/91)
In article <PPDuZ1w164w@dogface> writes: ?rcd@ico.isc.com (Dick Dunn) writes: ?> [users] are occasionally annoyed to find that csh rejects this syntax ?> with the confusing message "Invalid null command". ? ?What about ? cat /dev/null > splot ?to create an empty file? Not as, umm, Rube Goldberg-ish as your program, ?though. OVERKILL! There is a builtin command, `:' which works nicely, and is even easy to type. To empty a file, type :>file -- [rbj@uunet 1] stty sane unknown mode: sane
schaefer@ogicse.ogi.edu (Barton E. Schaefer) (04/05/91)
In article <127435@uunet.UU.NET> rbj@uunet.UU.NET (Root Boy Jim) writes: } In article <PPDuZ1w164w@dogface> writes: } ?rcd@ico.isc.com (Dick Dunn) writes: } ?> [users] are occasionally annoyed to find that csh rejects this syntax } ?> with the confusing message "Invalid null command". } ? } ?What about } ? cat /dev/null > splot } } OVERKILL! There is a builtin command, `:' which works nicely, That's not a builtin command, it's a degenerate case of a label for goto! For instance, empty:>splot if you think that's clearer. :-) -- Bart Schaefer schaefer@zipcode.com Z-Code Software Corporation schaefer@cse.ogi.edu
rbj@uunet.UU.NET (Root Boy Jim) (04/06/91)
In <19642@ogicse.ogi.edu> schaefer@ogicse.ogi.edu (Barton E. Schaefer) writes: >In article <127435@uunet.UU.NET> rbj@uunet.UU.NET (Root Boy Jim) writes: >} OVERKILL! There is a builtin command, `:' which works nicely, > >That's not a builtin command, it's a degenerate case of a label for goto! >For instance, > > empty:>splot > >if you think that's clearer. :-) RTFM! An excerpt: Built-In Commands Built-in commands are executed within the C shell. If a built-in command occurs as any component of a pipeline except the last, it is executed in a subshell. : Null command. This command is interpreted, but performs no action. alias [ name [ def ] ] -- [rbj@uunet 1] stty sane unknown mode: sane
gwyn@smoke.brl.mil (Doug Gwyn) (04/06/91)
In article <19642@ogicse.ogi.edu> schaefer@ogicse.ogi.edu (Barton E. Schaefer) writes: >} OVERKILL! There is a builtin command, `:' which works nicely, >That's not a builtin command, it's a degenerate case of a label for goto! > empty:>splot No! $ empty: empty:: not found $
jbw@bigbird.bu.edu (Joe Wells) (04/07/91)
In article <127627@uunet.UU.NET> rbj@uunet.UU.NET (Root Boy Jim) writes:
RTFM! An excerpt:
Built-In Commands
Built-in commands are executed within the C shell. If a
built-in command occurs as any component of a pipeline
except the last, it is executed in a subshell.
: Null command. This command is interpreted, but
performs no action.
alias [ name [ def ] ]
Not in the man page in Umax 4.3 which is directly derived from 4.3 BSD.
RTFM indeed!
--
Joe Wells <jbw@cs.bu.edu>jbw@bigbird.bu.edu (Joe Wells) (04/07/91)
In article <15724@smoke.brl.mil> gwyn@smoke.brl.mil (Doug Gwyn) writes:
No!
$ empty:
empty:: not found
$
What shell are you using here? We're talking about csh, remember?
Both these commands:
foo: > filename
foo:
work in csh under SunOS 4.1 and Umax 4.3.
--
Joe Wells <jbw@cs.bu.edu>