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From: jerry@oliveb.UUCP
Newsgroups: comp.unix.questions
Subject: Re: why does this script... ( : and # )
Message-ID: <1494@oliveb.UUCP>
Date: Sat, 20-Jun-87 00:11:50 EDT
Article-I.D.: oliveb.1494
Posted: Sat Jun 20 00:11:50 1987
Date-Received: Sun, 21-Jun-87 04:48:02 EDT
References: <913@rtech.UUCP>
Reply-To: jerry@oliveb.UUCP (Jerry F Aguirre)
Organization: Olivetti ATC; Cupertino, Ca
Lines: 46

The important thing to remember when using : in sh is that it is a null
command not a begin comment character.  So the following gotchas apply:

      -	The ":" must be followed by a white space or a sh metacharacter.

	: this is ok
	:>fu is also ok but will create the file fu
	:this is not ok because it looks for the command ":this".

      - The rest of the line will undergo normal filename, variable, and
	other metacharacter expansion.  So:

	    : Do I need this line?

	will fail when it tries to glob the question mark (assuming you
	don't have some 5 character file names that start with "line").
	Also, as previously mentioned the quotes must be balanced,
	perentheses have special meaning, etc.

      - A simicolon will end it, not just the end of line.

	    : This is ok; But this will try to execute "But"

It is safest to enclose the entire line in single quotes ala:

	    : 'this allows you to use ?()*$<>; without problems'

The only problem that leaves you is figuring out why:

	    : 'This line won't work'

If you think of : as being a faster version of:

	    /bin/echo>/dev/null arguments used but discarded

You will have a lot less problems.  Also interesting is that the :
command always returns true so it is also a faster replacement for
/bin/true.  With a little work it can also replace /bin/false.

			Jerry Aguirre

P.S.
    It is amazing the number of "experienced" shell programers who get
confused looks when faced with a syntax like.

		<inputfile grep pattern >outputfile