9.2 Macro Variables

The D compiler defines a set of built-in macro variables that you can use when writing D programs or interpreter files. Macro variables are identifiers that are prefixed with a dollar sign ($) and are expanded once by the D compiler when processing your input file. The following table describes the macro variables that the D compiler provides.

Table 9.1 D Macro Variables

Name	Description	Reference
`$[0-9]+`	Macro arguments	Section 9.3, “Macro Arguments”
`$egid`	Effective group ID	See the `getegid(2)` manual page.
`$euid`	Effective user ID	See the `geteuid(2)` manual page.
`$gid`	Real group ID	See the `getgid(2)` manual page.
`$pid`	Process ID	See the `getpid(2)` manual page.
`$pgid`	Process group ID	See the `getpgid(2)` manual page.
`$ppid`	Parent process ID	See the `getppid(2)` manual page.
`$sid`	Session ID	See the `getsid(2)` manual page.
`$target`	Target process ID	Section 9.4, “Target Process ID”
`$uid`	Real user ID	See the `getuid(2)` manual page

With the exception of the $[0-9]+ macro arguments and the $target macro variable, all of the macro variables expand to integers that correspond to system attributes, such as the process ID and the user ID. The variables expand to the attribute value associated with the current dtrace process or whatever process is running the D compiler.

Using macro variables in interpreter files enables you to create persistent D programs that you do not need to edit every time you want to use them. For example, to count all system calls, except those that are executed by the dtrace command, you would use the following D program clause containing $pid:

syscall:::entry
/pid != $pid/
{
  @calls = count();
}

This clause always produces the desired result, even though each invocation of the dtrace command has a different process ID. Macro variables can be used in a D program anywhere that an integer, identifier, or string can be used.

Macro variables are expanded only one time when the input file is parsed, not recursively.

Except in probe descriptions, each macro variable is expanded to form a separate input token and cannot be concatenated with other text to yield a single token.

For example, if $pid expands to the value 456, the D code in the following example would expand to the two adjacent tokens 123 and 456, resulting in a syntax error, rather than the single integer token 123456:

123$pid

However, in probe descriptions, macro variables are expanded and concatenated with adjacent text. For example, the following clause uses the DTrace pid provider to instrument the dtrace command:

# dtrace -c ./a.out -n 'pid$target:libc.so::entry'

Macro variables are only expanded one time within each probe description field and they may not contain probe description delimiters (:).