# var File

The var file is a pseudo file that
maps to the user’s TCL shell variables.

## Description

The var driver (most easily
used via the var file in the dm account) provides
access to TCL shell variables via a file interface.

A read using the variable name as the item-ID returns the
shell variable’s contents.

A read using a
TCL command surrounded by back-quotes executes the TCL command and
returns the results as if those results had been stored in an item.

A write using the variable name as the item-ID
is identical to running a TCL set on that variable.

A delete using the variable name as the item-ID
is identical to running a TCL unset on that variable.

A select`/`readnext loop is similar to the
 TCL penv command except that only the variable names are returned. Note that
 only user-defined variables are returned by the select command. Pre-set and
 system variables can only be queried by performing a direct read command.

## Example(s)

```
open "var"
*
* Read a shell variable
*
print @user
*
read xx from "user"
print xx
*
*
* Write a shell variable
*
execute "set myvar=abc"
*
write "abc" on "myvar"
*
* Delete a shell variable
*
execute "unset myvar"
*
delete "myvar"
*
* Display a list of user variables
*
execute "penv"
*
select
loop
readnext id then print id else exit
repeat
*
* Execute a TCL command
*
execute "display @‘who‘"
*
read xx from "‘who‘"
print xx
```

## See also

- [var](https://d3codex.com/definitions/var/)

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Source: https://d3codex.com/systemfiles/var-file/ - part of the D3Codex reference.