Difference Between NF and $NF

[Buck Turgidson]

I am new to awk. Not sure I understand the different context in which NF is
dereferenced in the 2nd example. I would appreciate if someone could
explain it in a sentence or two.

# Print every input line with more than 4 fields:

NF > 4

# Print every input line in which the last field is more than 4:

$NF > 4

[Kenny McCormack]

In article <r6jkc2-...@turf.turgidson.com>,

Looks like homework.

What's the difference between 4 and the 4th chicken (or the 4th anything) ?

[Chris F.A. Johnson]

Run the scripts and see what the difference is.

Read the man page.

Think.

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Chris F.A. Johnson http://cfaj.freeshell.org/shell
===================================================================
My code (if any) in this post is copyright 2005, Chris F.A. Johnson
and may be copied under the terms of the GNU General Public License

[Hrvoje Spoljar]

Buck Turgidson <jc...@hotmail.com> na grupi comp.lang.awk pise:

Ok maybe you can tell me what is the difference between

echo BLA

and

echo $BLA

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[Janis Papanagnou]

Buck Turgidson wrote:
> I am new to awk. Not sure I understand the different context in which NF is
> dereferenced in the 2nd example. I would appreciate if someone could
> explain it in a sentence or two.

Not quite sure what your problem is, but I suppose it's the "dereferencing"
concept.

> # Print every input line with more than 4 fields:
>
> NF > 4

The variable name NF is dereferenced as in most other programming languages.
The value of the (built-in) variable NF is compared against the value 4.

> # Print every input line in which the last field is more than 4:
>
> $NF > 4

You can access the 1st, 2nd, 3rd,... input field by $1 $2 $3 ...
Think of the numbers 1, 2, 3, ... as something like built-in variables.

The $ is the operator to access the fields. You can even use spaces: $ NF
Don't confuse the $ (access fields) in awk with $ (dereference) in shells.

If you specify a name after the $ operator it is considered to be a variable
and dereferenced to obtain the value stored in the variable, then the value
is used to access the field. NF is a built-in variable that carries always
a number. But you may as well use own variables: BEGIN { x = 5 } $x > 0

NF > 4 # deref(NF) > 4
$ NF > 4 # deref(fieldWithNr(deref(NF))) > 4

As in other languages you can ignore the implicit deref operations and focus
on the essential

NF > 4 # NF > 4
$ NF > 4 # fieldWithNr(NF) > 4

NF carries the number of fields, thus may be used to address the last field.

Janis

[Bill Marcum]

On Wed, 26 Jan 2005 20:40:28 +0000 (UTC), Hrvoje Spoljar
<fc...@k.cos.ue> wrote:
>
> Ok maybe you can tell me what is the difference between
>
> echo BLA
>
> and
>
> echo $BLA
>

"echo" is a shell command, not an awk command. Try this:
BLA=4
echo BLA
echo $BLA

Now for some real fun:
BLA=PATH
eval echo \$$BLA

[Hrvoje Spoljar]

Bill Marcum <bma...@iglou.com.urgent> na grupi comp.lang.awk pise:

So ? guy asked what is the difference betwen NF and $NF
so i thaugth maybe he is familiar with variables and strings
and example i gave would clear up the things... i never said echo was
awk command :-)