topic Re: : comment? in Operating System - HP-UX

: comment?

Deepak Extross — Wed, 07 Nov 2001 06:15:50 GMT

After years of using comments like this:
# this is a comment
today I came across a script with
: this is a comment.

Is there any compelling reason, other than to flummox the reader, for one to use a colon instead of the good old hash?

Re: : comment?

Deepak Extross — Wed, 07 Nov 2001 06:21:55 GMT

oops..that should have gone under 'languages'.

Re: : comment?

Animesh Chakraborty — Wed, 07 Nov 2001 06:34:20 GMT

Hi,
:this is a comment
sh: :this: not found.
:(

Re: : comment?

Scott Van Kalken — Wed, 07 Nov 2001 06:35:07 GMT

Dunno, but I've got another question:

if grep -qx $fs $EXCLUDE
then
: # To cater for ksh as ! command doesn't work
else
print - $block
fi

ksh wouldn't like the use of the : as it has special meaning.

Re: : comment?

Deepak Extross — Wed, 07 Nov 2001 06:43:44 GMT

Animesh,
Try with a space after the ':'

Re: : comment?

Sanjay_6 — Wed, 07 Nov 2001 06:57:56 GMT

Hi Deepak,

From animesh feedback it seems : does not act as a comment line signifier. It seems we have to live with the good old "#" only. Are you sure ":" is there to signify a comment line.

Hope this helps.

Regds

Re: : comment?

Animesh Chakraborty — Wed, 07 Nov 2001 07:28:29 GMT

Hi Deepak,
$: this is a comment
$ It works now with space
:)

Re: : comment?

Michael Tully — Wed, 07 Nov 2001 07:33:27 GMT

It seems that Deepak has a problem with spaces today..... Maybe I should have bought you that beer, you certainly now deserve it.

Cheers
-Michael

Re: : comment?

Ravi_8 — Wed, 07 Nov 2001 08:09:17 GMT

Hi, deepak

OLD IS GOLD. better stick to that.

Re: : comment?

Robin Wakefield — Wed, 07 Nov 2001 08:15:41 GMT

Hi Deepak,

The : or null command, is commonly used in if-else-fi blocks, where you cannot get away with executing nothing, e.g.

=====================================
#!/bin/ksh

if [ -f /etc/passwd ] ; then
#
else
echo passwd file missing
fi
=====================================

will fail - you need to put a : in place of the # for this to work. You could negate the if statement, but you may want to modify the script at a later stage with the existing if syntax.

Rgds, Robin.

Re: : comment?

Volker Borowski — Wed, 07 Nov 2001 08:20:59 GMT

Robin has a point !
I use a dummy command from good old assembler times, cause ":" can cause these questions.

NOP=1

No OPeration :-)

Keep Assembler alive :-)
Volker

Re: : comment?

Wodisch — Wed, 07 Nov 2001 12:03:18 GMT

Hello,

the command ":" is NOT a null command! Actually everything following it is evaluated, substituteted, and such.
So after
: ${x:=wow}
the variabel "$x" conatains "wow" only if it was previously empty!

HTH,
Wodisch

Re: : comment?

Darrell Allen — Wed, 07 Nov 2001 18:43:23 GMT

Here's my 2 cents:

: is not a comment. It is essentially a null command. It does not process command line args yet the shell still interprets them. It is sometimes used like a comment because it doesn't do anything and the comments are ignored arguments. The shell is doing the work.

You can create your own null command by creating an empty file. It will work just like Wodisch's example.

Darrell

Re: : comment?

Deepak Extross — Thu, 08 Nov 2001 02:45:16 GMT

#: ${x:=wow}

#echo $x
wow

#: echo $x

whee..aint this fun?

Re: : comment?

Wodisch — Thu, 08 Nov 2001 07:26:37 GMT

evaluated - not executed! :-)