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DCL Lexical Functions are a group of built-in functions, part of DCL itself, which return information (data) about DCL values, your (interactive or batch) process, and/or the VMS system environment itself.
There are 45 Lexical Functions (as of VMS v8.4 and prior), and each is conventionally named with the characters
F$ as prefix to the function's descriptive name; e.g.,
You can use these Lexical Functions in command files (scripts, the typical use), or even interactively on the command line itself to experiment and see what each one does. Lexical Functions are an essential DCL coders' resource, and allow your command files to be written to be general purpose and powerful.
If you try to look for DCL help on any of these Lexical Functions like this:
$ HELP F$EDIT
…you'll be disappointed with an warning message like this:
Sorry, no documentation on F$EDIT Additional information available: := = @ ABS ACCOUNTING ACL_Editor ... ALLOCATE ANALYZE APPEND ASSIGN ATTACH ... Topic?
The trick is to know that you need to get
HELP on the
Lexicals topic itself, so:
$ HELP LEX F$EDIT (...displays the help-text for the F$EDIT lexical function...)
$ HELP LEXICALS Lexicals A set of functions that return information about character strings and attributes of the current process. Additional information available: F$CONTEXT F$CSID F$CUNITS F$CVSI F$CVTIME ... (...displays the complete list of lexical functions...)
The HELP Lexicals entry lists the Lexical Functions alphabetically, which may not be particularly helpful in learning them. See the wiki article Catalog of DCL Lexical Functions for a category/functional list of these Lexicals.
It's easy to play with and learn most of the Lexical Functions on the DCL command line (a few are truly designed for best-use in command files).
First, for brevity, let's create a shorthand command alias (symbol) for the longer/hard-to-type command “
WRITE SYS$OUTPUT” (and put the following global symbol definition in your own
SYS$LOGIN:LOGIN.COM file, if you like):
$ wso == "WRITE sys$output" ! you might prefer another alias name, like "say" or "out"... $ ! Now we can just do this: $ wso "This is a test!" This is a test! $
Now you can do things like this:
$ wso F$TIME() 20-NOV-2018 15:33:43.06 $
$ string = "test" $ wso F$LOCATE( string, "This is a test..." ) 10 $ ! The substring "test" is found at location/position 10 in the larger string. $ ! Position 0 is the first character of that string.
$ wso $ wso F$TRNLNM( "SYS$DISK" ) DSA2: $ wso F$DIRECTORY() [LRICKER] $ wso F$SEARCH( "LOGIN*.COM" ) DSA2:[LRICKER]LOGIN.COM;10 $
$ wso F$MODE() INTERACTIVE $
$ wso F$TRNLNM( "SYS$SYSDEVICE", "LNM$SYSTEM_TABLE" ) $32$DKA0: $
$ fname = "SYS$LOGIN:LOGIN.COM" $ wso F$PARSE( fname, , , "NAME", "SYNTAX_ONLY") + F$PARSE( fname, , , "TYPE", "SYNTAX_ONLY" ) LOGIN.COM $
$ start = F$TIME() $ ! ...wait a bit... $ ! ...dum-de-dum... $ $ wso F$DELTA_TIME( start, F$TIME(), "DCL") 0-00:00:21.07 $ ! Twenty-one seconds later!...