awk question

[Jim Trigg]

Frighteningly enough, the syntax "< file  command" does work...

Jim

On October 5, 2015 5:58:12 PM EDT, Polytropon <freebsd at edvax.de> wrote:
>On Mon, 05 Oct 2015 17:44:55 -0400, Quartz wrote:
>> 
>> > The form "input | step1 | step2 | step3 | step4>  result" usually
>> > is more readable
>> 
>> That's what I meant my being easier to understand conceptually. I
>agree 
>> about being more readable- even though this format sometimes needs
>the 
>> 'useless cat' it's often my preferred coding style, especially in 
>> scripts where the input might change around.
>
>And the "useless cat" method also makes it easy to test the
>script with varying input (for example, pre-generated test
>input) before it "goes live". It also makes it easier to
>"extend" the pre- or post-processing commands with new ones.
>
>
>
>> > Additionally, awk isn't that hard to learn. Reading "man awk" will
>> > provide you with a good background. And if you're already a C
>> > programmer, you'll see that many things you can do in C will also
>> > work similarly in awk, which _might_ not even be a good thing. :-)
>> 
>> The problem with awk is the whole BEGIN/END/braces thing and how
>commas 
>> interact with the operands.
>
>It's not that hard:
>
>BEGIN { ... } will be executed _before_ any input is processed,
>END { ... } will be executed _after_ all input has been processed.
>/pattern/ { ... } will be executed for each matching input line,
>(condition) { ... } will be executed when the condition is true,
>and { ... } will be executed for _every_ input line.
>
>Regarding commas: You can use the "print a b c" form as well as
>the more sophisticated C-like printf("format string", a, b, c)
>form. For all other functions, commas are argument separators
>just like in many other programming languages.
>
>	% echo "a b c" | awk '{ print $3 $1 $2 }'
>	cab
>	% echo "a b c" | awk '{ print $3, $1, $2 }'
>	c a b
>	% echo "a b c" | awk '{ printf("%s-%s-%s\n", $3, $1, $2); }'
>	c-a-b
>
>Those are the three "main methods" of printing: concatenated,
>separated by a space, and custom formatted string. And the
>semicolon is optional, it's just my C-contamination. :-)
>
>
>> It's not very much like sh or C syntax (or 
>> any other syntax) and new users tend to get really confused.
>
>Hmmm... I don't know, could you provide an example where you
>would say, like, "this is not intuitive" or even "this does
>something totally strange"?
>
>
>
>> Also, different versions of awk handle math (esp floating point) with
>
>> different rounding/precision/overflow, making calculations vary
>between 
>> installations, only further adding to the confusion.
>
>Yes, this is true, but keep in mind what awk is: a "pattern-directed
>scanning and processing language". If you want higher precision
>math, use system("<math stuff> | dc") and incorporate the result;
>awk isn't really for math, but integer math is usually fine. :-)
>
>
>
>-- 
>Polytropon
>Magdeburg, Germany
>Happy FreeBSD user since 4.0
>Andra moi ennepe, Mousa, ...
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