Interpreter Files

Similar to your shell and utilities such as awk(1) and perl(1), dtrace(1M) can be used to create executable interpreter files. An interpreter file begins with a line of the form:

#! pathname arg

where pathname is the path of the interpreter and arg is a single optional argument. When an interpreter file is executed, the system invokes the specified interpreter. If arg was specified in the interpreter file, it is passed as an argument to the interpreter. The path to the interpreter file itself and any additional arguments specified when it was executed are then appended to the interpreter argument list. Therefore, you will always need to create DTrace interpreter files with at least these arguments:

#!/usr/sbin/dtrace -s

When your interpreter file is executed, the argument to the -s option will therefore be the pathname of the interpreter file itself. dtrace will then read, compile, and execute this file as if you had typed the following command in your shell:

# dtrace -s interpreter-file

The following example shows how to create and execute a dtrace interpreter file. Type the following D source code and save it in a file named interp.d:

#!/usr/sbin/dtrace -s
BEGIN
{
    trace("hello");
    exit(0);
}

Mark the interp.d file as executable and execute it as follows:

# chmod a+rx interp.d
# ./interp.d
dtrace: script './interp.d' matched 1 probe
CPU     ID                    FUNCTION:NAME
  1      1                           :BEGIN   hello
#

Remember that the #! directive must comprise the first two characters of your file with no intervening or preceding whitespace. The D compiler knows to automatically ignore this line when it processes the interpreter file.

dtrace uses getopt(3C) to process command-line options, so you can combine multiple options in your single interpreter argument. For example, to add the -q option to the preceding example you could change the interpreter directive to:

#!/usr/sbin/dtrace -qs

If you specify multiple option letters, the -s option must always end the list of boolean options so that the next argument (the interpreter file name) is processed as the argument corresponding to the -s option.

If you need to specify more than one option that requires an argument in your interpreter file, you will not be able to fit all your options and arguments into the single interpreter argument. Instead, use the #pragma D option directive syntax to set your options. All of the dtrace command-line options have #pragma equivalents that you can use, as shown in Chapter 16, Options and Tunables.