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From: Janis Papanagnou <janis_papanag...@hotmail.com>
Newsgroups: comp.lang.awk
Subject: Re: Stop Reading Input Without EOF/nextfile/getline
Date: Wed, 05 Sep 2012 00:57:35 +0200
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On 04.09.2012 22:53, Ed Morton wrote:
> I was recently trying to answer a question and came across a problem I
> don't know if there is an answer to: how can you stop reading from an
> input stream without waiting for EOF or invoking getline or (in gawk)
> nextfile?
> 
> For example, let's say you have a script that prompts a user for some
> numeric value and then uses that value to multiply a set of other values
> stored in a file. e.g.:
> 
> $ cat file
> 4
> 5
> 2
> 
> $ awk -f mult.awk file        
> Enter multiplier: 3
> 3 * 4 = 12
> 3 * 5 = 15
> 3 * 2 = 6
> 
> $ awk -f mult.awk file
> Enter multiplier: 4
> 4 * 4 = 16
> 4 * 5 = 20
> 4 * 2 = 8
> 
> That could be implemented as either of these:
> 
> -------
> $ cat mult_getline.awk
> BEGIN {
>    printf "Enter multiplier: "
>    getline mult < "-"
> }
> 
> { printf "%d * %d = %d\n", mult, $0, mult * $0 }
> -------
> $ cat mult_nextfile.awk
> BEGIN {
>    ARGV[ARGC++] = ARGV[1]; ARGV[1] = "-"
>    printf "Enter multiplier: "
> }
> 
> NR==FNR {
>    mult = $0
>    nextfile
> }
> 
> { printf "%d * %d = %d\n", mult, $0, mult * $0 }
> -------
> 
> Is there any way to implement it without using getline or nextfile and
> without the user explicitly having to enter a control-D or anything else
> after their multiplier number, and without reading the whole data file
> into an array? The main point is to be able to stop reading the first
> input stream before an EOF is encountered.

Well, how should awk know about end of file? (Using close() doesn't seem
to work.)

[OT] You can force EOF at shell level...

  awk '
    BEGIN { printf "Enter multiplier: " }
    NR==FNR { mult = $0 ; next }
    { printf "%d * %d = %d\n", mult, $0, mult * $0 }
  ' <(head -1) file

No pure awk solution, but a concise and simple pattern at least.

Janis

> 
>    Ed.
> 
> 
> Posted using www.webuse.net 
>