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From: RALPH@UHHEPG.BITNET
Newsgroups: comp.os.vms
Subject: Command input from a file continued, and maybe a bug in VMS
Message-ID: <8708071731.AA11054@ucbvax.Berkeley.EDU>
Date: Fri, 7-Aug-87 13:32:05 EDT
Article-I.D.: ucbvax.8708071731.AA11054
Posted: Fri Aug  7 13:32:05 1987
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Date:  5-AUG-1987 20:29:29.00
From: Ralph Becker-Szendy RALPH AT UHHEPG
To:   B_INFOVAX,RALPH
Subj: Command input from a file continued, and maybe a bug in VMS
Hi everyone out there

Thanks a lot for all the help i got for my little problem with input/output
redirection:

> I want something like the DCL @ command: If the command is @filespec,
> the command interpreters should open this file, and present it (line
> by line) to CLI$DCL_PARSE and other routines, which read special input
> from a terminal.

Unfortunately, none of the help got me anywhere (or rather: some of them
seem to get me into bug-land). I was offered really big packages for this
purpose (mostly written in straight FORTRAN), but they are bulky, and would
require a lot of recoding (since they would completely replace all the
CLI$... routines), and a lot of understanding them , and i wanted a quick
afternoon-hack.

Several fellow netpeople pointed mo towards the LIB$SET_LOGICAL routine,
which seems to do what i want: assign SYS$INPUT or SYS$OUTPUT to a file
(instead of the terminal) for a while while the programs runs. Unfortunately,
i found some quite strange behaviour. Look at the following short FORTRAN
program. It should read one line from the terminal, print it, and then
redirect SYS$INPUT to the file INPUT.FILE, read one line from there, print it,
and exit:

      PROGRAM MINITEST ! mini version without loops or error handling

      IMPLICIT NONE
      CHARACTER INPUT*80
      INTEGER LENGTH, STATUS

      INTEGER  LIB$GET_INPUT, LIB$SET_LOGICAL
      EXTERNAL LIB$GET_INPUT, LIB$SET_LOGICAL
      INCLUDE '($RMSDEF)' ! not yet needed, for recognizing EOFs later

      STATUS = LIB$GET_INPUT(INPUT, 'From Terminal: ', LENGTH)
      IF (.NOT.STATUS) CALL LIB$SIGNAL(%VAL(STATUS))
      PRINT *, 'Input from terminal was ', INPUT(1:LENGTH)

      STATUS = LIB$SET_LOGICAL('SYS$INPUT', 'INPUT.FILE')
      IF (.NOT.STATUS) CALL LIB$SIGNAL(%VAL(STATUS))

      STATUS = LIB$GET_INPUT(INPUT, 'From File: ', LENGTH)
      IF (.NOT.STATUS) CALL LIB$SIGNAL(%VAL(STATUS))
      PRINT *, 'Input from file was ', INPUT(1:LENGTH)

      STOP
      END

Well, it does the following:
- it reads one line from the terminal and prints it
- it does reassign SYS$INPUT to INPUT.FILE (you can check it by inserting
  a call to LIB$SYS_TRNLOG('SYS$INPUT'... after the assign)
- it reads ANOTHER LINE FROM THE TERMINAL and prints it !
- Now, back at DCL, a SHOW TRANS SYS$INPUT will yield INPUT.FILE (obviously),
  so i try running the program again:
- it reads the first line from the file (obviously) and prints it
- it reads the second line from the file (still obvious) and prints it.
All variations of the program (like read many lines instead of one, check
for EOFs and such, which i ommited here for the sake of brevity) seem
completely consistent: what counts for LIB$INPUT is not the translation of
SYS$INPUT at the time you call it, but AT THE TIME THE PROGRAM WAS INVOKED.
If SYS$INPUT points to the terminal at the beginning of the program, all
the LIB$SET_LOGICALS can't change the mind of LIB$GET_INPUT.

The only question it: why is this so ? What use is LIB$SET_LOGICAL in this
case ? Is this a bug ? Should i SPR it ? Am i stupid ? Is there something
tricky (maybe using the right logical name table) i overlooked ?

signed: confused

Ralph Becker-Szendy
University of Hawaii / High Energy Physics Group