The ZWRITE command displays the current value of one or more local , alias variables, ISVs, or global variables. ZWRITE formats its output so that each item in the display forms a valid argument to a SET @ command. This means ZWRITE encloses string values in quotes and represents non-graphic (control) characters in $CHAR() syntax.

The format of the ZWRITE command is:

ZWR[ITE][:tvexpr] [zwrglvn[,...]]

ZWRITE Format for Alias Variables

ZWRITE and ZSHOW "V" dump the values of alias variables, alias container variables, and the associated data as described below, in ZWRITE format. In the ZWRITE format, the contents of an array are displayed with the name associated with that array that appears first in the lexical ordering of names. GT.M displays both the unsubscripted and subscripted nodes and values, appending a notational space-semicolon-asterisk (";*") sequence to the unsubscripted value, if any. The ZWRITE format output can be read into a GT.M process with the commands Read x and Set @x (where x is any name) executed in a loop. ";*" acts as a comment ignored by the SET command. In the following example, since A and C are aliases associated with the same array, the nodes of that array are output with A, which occurs lexically before C, even though the values were assigned to C:

GTM>Set C=1,C("Malvern")="Wales",*A=C,*B(-3.14)=C
GTM>ZSHow "V" ; ZWRite would produce the same output
A=1 ;*
GTM>ZWRite C ; Only one is name associated with the array on this ZWRite command
C=1 ;*

Continuing the example, if the variables selected for the ZWRITE command do not include any of the the associated alias variables, the output shows only the reference, not the data:

GTM>ZWRITE B ; B only has a container

When ZWRITE / ZSHOW "V" encounters an alias container for an array with no current alias variable, it uses a name $ZWRTACn as the made-up name of an alias variable for that array, where n is an arbitrary but unique integer. The SET command recognizes this special name, thus enabling the output of a ZWRITE / ZSHOW "V" to be used to recreate alias containers without associated alias variables. Continuing the above example:

GTM>Kill *A,*C ; Delete alias variables and associations, leaving only the container
$ZWRTAC1=3 ;*

ZWRITE produces $ZWRTACn names to serve as data cell anchors which SET @ accepts as valid set left targets. $ZWRTACn names are created and destroyed when using ZWRITE output to drive restoration of a previously captured variable state. Except for their appearance in ZWRITE output and as left-hand side SET @ targets, they have no function. Other than SET, no other commands can use $ZWRTAC* in their syntax. Although $ZWRTACn superficially looks like an intrinsic special variable (ISV), they are not ISVs. $ZWRTACn with no subscripts can serve as the target (left side of the equals-sign) of a SET * command. SET $ZWRTAC (no trailing integer) deletes all data cell associations with the $ZWRTAC prefixed aliases. GT.M only recognizes the upper-case unabbreviated name and prefix $ZWRTAC.

When ZWRITE displays values for an alias variable, it appends a " ;*" to the name which visually tags the alias without interfering with use of ZWRITE output as arguments to a SET @. ZWRITE can only identify alias variables when at least two aliases for the same data match its argument. When ZWRITE encounters an alias container variable with no current associated alias, it uses the ZWRTAC mechanism to expose the data; SET @ can restore data exposed with the ZWRTAC mechanism.

[Caution] Caution

FIS strongly recommends that you should not create or manipulate your own $ZWRTACn "variables". They are not part of the supported functionality for implementing alias variables and containers, but are rather a part of the underlying implementation that is visible to you, the GT.M user. FIS can arbitrarily, for its own convenience change the use of $ZWRTAC in GT.M at any time. They are only documented here since you may see them in the output of ZWRITE and ZSHOW "V".

Examples of ZWRITE


GTM>ZWRITE ^?1"%"2U(0:":",)

This command displays the descendants of all subscripts between 0 and ":" of all global names starting with a "%" and having two upper case letters -- for example, "%AB".



This command displays all of the third level nodes with a subscript of 3 for local variable A.


ZWRITE ?1"A".E(?1"X"3N)

This displays data for any local variables starting with "A", optionally followed by any characters, and having any subscripts starting with "X" followed by three numerics.


GTM>Set A=1,*B=A ; Create an array and an alias association
GTM>ZWRite ; Show that the array and association exist
A=1 ;*