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From: Janis Papanagnou on 30 Mar 2010 13:41
Ed Morton wrote:
>>[...]
>
> Since you don't use "$" to dereference the value of awk variables (other
> than $1, $2, etc.) then doing

You seem to imply that 1, 2, etc. are identifiers of [special] variables
that are an exception (compared to other variables) in being dereferenced
by the $ operator. But the numbers are no special, they are just what is
expected behind a $ operator; any expression that evaluates to a number.
In the "A,K&W" Book the $ is thus named as "field" operator. It allows
not only for expressions like $1 or $x, where x contains anything that
evaluates to a number[*], but also $NF, $(NF-1), $ 1, $ x, $ f( 2 ), with
any appropriate function f, or even $ /hi there/ .

N.B.: I've tested the funny looking $/hi there/ application only with my
GNU awk, so I'd be interested to hear from other awk's behaviour.

Janis

[*] Strings and booleans included, and, as shown, even regexp patterns.

>
> x=2
> printf "%s\n",x
> printf "%s\n",$x
>
> in awk is equivalent to:
>
> x=2
> printf "%s\n" "$x"
> eval printf '"%s\n"' \"\${$x}\"
>
> in shell IF the value of x is a number. If the value of x is not a
> number then in awk $x is the same as $0.
>[...]
From: Ed Morton on 30 Mar 2010 16:23
On Mar 30, 12:41 pm, Janis Papanagnou <janis_papanag...(a)hotmail.com>
wrote:
> Ed Morton wrote:
> >>[...]
>
> > Since you don't use "$" to dereference the value of awk variables (other
> > than $1, $2, etc.) then doing
>
> You seem to imply that 1, 2, etc. are identifiers of [special] variables
> that are an exception (compared to other variables) in being dereferenced
> by the $ operator. But the numbers are no special, they are just what is
> expected behind a $ operator; any expression that evaluates to a number.

I tend to think of them as variables since you can read and write them
as you would variables but you are right. Thanks for pointing that
out.

> In the "A,K&W" Book the $ is thus named as "field" operator. It allows
> not only for expressions like $1 or $x, where x contains anything that
> evaluates to a number[*], but also $NF, $(NF-1), $ 1, $ x, $ f( 2 ), with
> any appropriate function f, or even  $ /hi there/ .
>
> N.B.: I've tested the funny looking $/hi there/ application only with my
> GNU awk, so I'd be interested to hear from other awk's behaviour.

Here's a few from Solaris:

$ echo "hi there\nlo there" | gawk '{print NR,$/hi there/}'
1 hi
2 lo there

$ echo "hi there\nlo there" | /usr/xpg4/bin/awk '{print NR,$/hi
there/}'
1 hi
2 lo there

$ echo "hi there\nlo there" | nawk '{print NR,$/hi
there/}'
nawk: syntax error at source line 1
context is
{print >>> NR,$/ <<< hi there/}
nawk: illegal statement at source line 1

$ echo "hi there\nlo there" | oawk '{print NR,$/hi there/}'
awk: syntax error near line 1
awk: illegal statement near line 1

Regards,

Ed.

> Janis
>
> [*] Strings and booleans included, and, as shown, even regexp patterns.
>
>
>
>
>
> >     x=2
> >     printf "%s\n",x
> >     printf "%s\n",$x
>
> > in awk is equivalent to:
>
> >     x=2
> >     printf "%s\n" "$x"
> >     eval printf '"%s\n"' \"\${$x}\"
>
> > in shell IF the value of x is a number. If the value of x is not a
> > number then in awk $x is the same as $0.
> >[...]- Hide quoted text -
>
> - Show quoted text -

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