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 systems.8
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 awk as if you had
typed ‘awk -f advice’:
$ chmod +x advice
$ ./advice
-| Don't Panic!
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.
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awk is an interpreted language. This means that the
awk utility reads your program and then processes your data
according to the instructions in your program. (This is different
from a compiled language such as C, where your program is first
compiled into machine code that is executed directly by your system’s
processor.) The awk utility is thus termed an interpreter.
Many modern languages are interpreted.
The line beginning with ‘#!’ lists the full file name of an
interpreter to run and a single 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. (Note that on
many systems awk is found in /usr/bin instead of
in /bin.)
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 section Predefined 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’). (d.c.)
Don’t rely on the value of ARGV[0]
to provide your script name.
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