| Title: | VAX and Alpha VMS |
| Notice: | This is a new VMSnotes, please read note 2.1 |
| Moderator: | VAXAXP::BERNARDO |
| Created: | Thu Jan 23 1997 |
| Last Modified: | Fri Jun 06 1997 |
| Last Successful Update: | Fri Jun 06 1997 |
| Number of topics: | 703 |
| Total number of notes: | 3722 |
I have just had a customer report a problem with the OpenVMS V7.1
PIPE command. He reported that he could use symbol substitution
in a pipe command but I found with testing that the symbol couldn't
be used if it was defined in the same PIPE command. If the symbol
is defined before the PIPE command is executed it can be used.
A symbol defined in a PIPE command can be SHOWed in the same PIPE
command it is defined in.
Should this be QAR'd? I've attached output from my testing.
Robin Davey
OpenVMS Support
CSC/CTH
CTHU62> x:==login.com ! define a symbol
CTHU62> pipe show symb x ; dir 'x ! use symbol in pipe command
X == "LOGIN.COM" ! can show symbol
Directory SYS$SYSDEVICE:[TEST]
LOGIN.COM;1 1 5-MAY-1997 15:05:09.51
Total of 1 file, 1 block. ! can use symbol
CTHU62> del/sym/glo x ! delete the symbol
! define symbol in the pipe command
CTHU62> pipe x:==login.com ; show symb x ; dir 'x
X == "LOGIN.COM" ! can still show symbol
Directory SYS$SYSDEVICE:[TEST]
LOGIN.COM;1 1 5-MAY-1997 15:05:09.51
TEST.TXT;1 1 5-MAY-1997 15:05:41.14
Total of 2 files, 2 blocks. ! symbol appears to be ignored
totally
! hit up-arrow & redo pipe command
CTHU62> pipe x:==login.com ; show symb x ; dir 'x
X == "LOGIN.COM" ! show symbol always works
Directory SYS$SYSDEVICE:[TEST]
LOGIN.COM;1 1 5-MAY-1997 15:05:09.51
Total of 1 file, 1 block. ! using symbol now works but I
assume it's because it was
predefined by the previous
pipe command
| T.R | Title | User | Personal Name | Date | Lines |
|---|---|---|---|---|---|
| 565.1 | Answered my own question... | KAOFS::R_DAVEY | Robin Davey CSC/CTH dtn 772-7220 | Mon May 05 1997 20:09 | 7 |
I think I just answered my own question.
The CLI does all symbol substitution in the command line before
any execution is performed. Is this correct?
Robin
| |||||
| 565.2 | Symbol Substitution Occurs Early... | XDELTA::HOFFMAN | Steve, OpenVMS Engineering | Mon May 05 1997 20:46 | 5 |
: The CLI does all symbol substitution in the command line before : any execution is performed. Is this correct? Yes, this is correct. | |||||
| 565.3 | Another possibility along the same lines | GIDDAY::GILLINGS | a crucible of informative mistakes | Tue May 06 1997 03:12 | 43 |
Also be aware that some PIPE commands will generate subprocesses, it is therefore possible to invent command sequences where it's impossible for symbol definitions to propogate. The subprocesses work in parallel so you have to stop thinking linearly. For example $ PIPE SHOW TIME | - ! Executed in MAIN process x=="SWAPPER" ; show system | - ! Executed in subprocess 1 SEARCH SYS$INPUT 'X' ; SHOW SYM X ! Executed in subprocess 2 %DCL-W-INSFPRM, missing command parameters - supply all required parameters %DCL-W-UNDSYM, undefined symbol - check validity and spelling $ show sym x ! back in main process %DCL-W-UNDSYM, undefined symbol - check validity and spelling The global symbol X only exists in subprocess 1. Since both subprocesses are spawned from the parent (see AUDIT messages below), there is no way for subprocess 2 to "see" any symbols defined in subprocess 1. %%%%%%%%%%% OPCOM 6-MAY-1997 13:03:05.22 %%%%%%%%%%% Message from user AUDIT$SERVER on FLANGE Security alarm (SECURITY) on FLANGE, system id: 60860 Auditable event: Subprocess or pipe subprocess login Event time: 6-MAY-1997 13:03:05.22 PID: 0000033A Parent PID: 00000140 Process name: GILLINGS_1 Parent process name: GILLINGS Username: GILLINGS Parent username: GILLINGS Process owner: [TSC,GILLINGS] Image name: $7$DKA100:[SYS0.SYSCOMMON.][SYSEXE]LOGINOUT.EXE %%%%%%%%%%% OPCOM 6-MAY-1997 13:03:05.33 %%%%%%%%%%% Message from user AUDIT$SERVER on FLANGE Security alarm (SECURITY) on FLANGE, system id: 60860 Auditable event: Subprocess or pipe subprocess login Event time: 6-MAY-1997 13:03:05.32 PID: 0000033B Parent PID: 00000140 Process name: GILLINGS_2 Parent process name: GILLINGS Username: GILLINGS Parent username: GILLINGS Process owner: [TSC,GILLINGS] Image name: $7$DKA100:[SYS0.SYSCOMMON.][SYSEXE]LOGINOUT.EXE (there are actually another 2 subprocesses spawned as well, I'm not sure why). John Gillings, Sydney CSC | |||||