9.1 Interpreter Files

Similar to your shell and utilities such as awk and perl, dtrace 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 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 is be the pathname of the interpreter file itself. dtrace then reads, compiles, and executes 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

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
  0      1                           :BEGIN   hello                            

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

dtrace uses getopt() 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 options so that the next argument (the interpreter file name) is processed as the argument to the -s option.

If you need to specify more than one option that requires an argument in your interpreter file, use the #pragma D option directive to set your options. Several dtrace command-line options have #pragma equivalents that you can use, as described in Chapter 10, Options and Tunables.