Hi,

I'm looking at a internal script & see this below if statement but I
don't understand it.  Could someone please explain what it means if
you don't mind?

#!/bin/ksh

row=0
if [ $row > 0 ]
then
:              # note I don't understand what " : " notation
actually does & means
else
.......
fi

TIA,
-Chris

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On 2007-04-26, lazyboy_2k@yahoo.com wrote:
> Hi,
>
> I'm looking at a internal script & see this below if statement but I
> don't understand it.  Could someone please explain what it means if
> you don't mind?

The script is broken.

> #!/bin/ksh
>
> row=0
> if [ $row > 0 ]

That should be:

if [ $row -gt 0 ]

In the shell, '>' is the redirection operator, not a comparison
operator, although some shells allow it as a string comparison
operator if it is escaped, e.g.:

if [ "$q" \> alpha ]

>   then
>      :              # note I don't understand what " : " notation actually does & 
means

It is a command that does nothing. Any arguments will be expanded,
$_ will be set, and any side effects will be performed:

q=
: ${q:=qwerty} asdfg
printf "%s\n" "$q" "$_"

>   else
>      ........
> fi


--
Chris F.A. Johnson, author   |    <http://cfaj.freeshell.org>
Shell Scripting Recipes:     |  My code in this post, if any,
A Problem-Solution Approach  |         is released under the
2005, Apress                 |    GNU General Public Licence

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2007-04-26, 10:29(-07), lazyboy_2k@yahoo.com:
> Hi,
>
> I'm looking at a internal script & see this below if statement but I
> don't understand it.  Could someone please explain what it means if
> you don't mind?
>
> #!/bin/ksh
>
> row=0
> if [ $row > 0 ]
>   then
>      :              # note I don't understand what " : " notation
> actually does & means
>   else
>      ........
> fi
[...]

Some early versions of ksh didn't have the "!" keyword, so if
you wanted to do: "if not this, then that", then you had to do
"if this, then do-nothing else that".

So:

if [ "$row" -gt 0 ]
then
:
else
..
fi

is the same as standard sh's:

if ! [ "$row" -gt 0 ]
then
..
fi

Note that the "[" command also has a "!" operator even in old
versions of ksh:

if [ ! "$row" -gt 0 ]
then
..
fi

There's also:

if [ "$row" -le 0 ]

though that's not strictly equivalent, for instance when "$row"
doesn't expand to a valid number.

--
Stéphane

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