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1.1.4 Executable awk Programs

Once you have learned awk, you may want to write self-contained awk scripts, using the `#!' script mechanism. You can do this on many Unix systems1 as well as on the GNU system. For example, you could update the file advice to look like this: 

     #! /bin/awk -f
     
     BEGIN { print "Don't Panic!" }

After making this file executable (with the chmod utility), simply type `advice' at the shell and the system arranges to run awk2 as if you had typed `awk -f advice': 

     $ chmod +x advice
     $ advice
     -| Don't Panic!

(We assume you have the current directory in your shell's search path variable (typically $PATH). If not, you may need to type `./advice' at the shell.)

Self-contained awk scripts are useful when you want to write a program that users can invoke without their having to know that the program is written in awk.

Advanced Notes: Portability Issues with `#!'

Some systems limit the length of the interpreter name to 32 characters. Often, this can be dealt with by using a symbolic link.

You should not put more than one argument on the `#!' line after the path to awk. It does not work. The operating system treats the rest of the line as a single argument and passes it to awk. Doing this leads to confusing behavior—most likely a usage diagnostic of some sort from awk.

Finally, the value of ARGV[0] (see Built-in Variables) varies depending upon your operating system. Some systems put `awk' there, some put the full pathname of awk (such as /bin/awk), and some put the name of your script (`advice'). Don't rely on the value of ARGV[0] to provide your script name.

Footnotes

[1] The `#!' mechanism works on Linux systems, systems derived from the 4.4-Lite Berkeley Software Distribution, and most commercial Unix systems.

[2] The line beginning with `#!' lists the full file name of an interpreter to run and an optional initial command-line argument to pass to that interpreter. The operating system then runs the interpreter with the given argument and the full argument list of the executed program. The first argument in the list is the full file name of the awk program. The rest of the argument list contains either options to awk, or data files, or both.