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Author Topic: Fun with AWK and GAWK  (Read 244 times)

Weaver

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Fun with AWK and GAWK
« on: June 04, 2019, 05:04:55 AM »

I had a go at writing my first ever AWK program. This is a tool that is a bit like the C preprocessor where it handles #ifís bug applied to XML Firebrick config files.

I have invented a system where significant comments are used, comments that begin with a special very long distinctive marker and the rest of the comment contains some declaration or command. This can be a #if-like command which causes the following section to be deleted or left in.

The reason for this is that the Firebrick FB2700 and above support USB NICs for 3G and 4G (aka Ďdonglesí) but the FB2500 has no usb interface. Unfortunately the FB2500 gets upset if you even mention usb or dongles, so you cannot use a single config file with both models. I have one of each, and I donít want to have the nightmare of maintaining two files and having to keep them both up to date.

So using the #if-like conditional section markers I can hide FB2700 usb- and dongle-related stuff from an FB2500 by automatically removing the marked section, and if possible I can put in alternative sections too. So there are FB2700-only sections.

Anyway to attempt to cut a long story short, wrote this in AWK, worked fine. It preprocesses an input FB2700-format Firebrick XML config file, does the right thing with it. Alternatively it can optionally convert FB2700 format into a format suitable for upload into an FB2500, ie edited to be without mentions of usb and dongles.

However when I copied the AWK program to a new Raspberry Pi system running Ubuntu v16.xx, AWK spat out a big load of syntax errors. After tearing my hair out for ages, I worked out that this was a completely different AWK interpreter from whatever was on the other Pi. Installed GAWK and then the program worked fine. Whatever AWK executable I had been running before was lacking some enhanced facilities, the lack of support for the GAWK switch statement was the main casualty as far as I could tell.

So what should I do in general? Change the first line to be #!/bin/gawk -f ? To show that it really needs GAWK ?

What should I do about installing the program - it needs to handle its dependency- so needs to do an apt-get install -y gawk or some such ?

My other problem : Isnít apt-get a flavour/distro specific command anyway? Is there something more portable solid command that I can use for installing such a package?
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burakkucat

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Re: Fun with AWK and GAWK
« Reply #1 on: June 04, 2019, 05:52:22 PM »

So what should I do in general? Change the first line to be #!/bin/gawk -f ? To show that it really needs GAWK ?

Yes. That would be the most sensible.

Quote
What should I do about installing the program - it needs to handle its dependency- so needs to do an apt-get install -y gawk or some such ?

My suggestion would be to use --

aptitude install gawk
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petef

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Re: Fun with AWK and GAWK
« Reply #2 on: June 06, 2019, 08:30:03 PM »

If you are working with XML then XSLT would be a more natural fit. XSLT has similarities with AWK being based on pattern matching but using XML syntax.

Another alternative is Python + lxml.
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Weaver

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Re: Fun with AWK and GAWK
« Reply #3 on: June 07, 2019, 01:39:48 AM »

I have done a huge amount of XSLT. Iím writing it all in AWK as a learning project. I might have a go at writing the tool in D as D has a very powerful regex engine and I need that for part of it.

The awk code is just a state machine and the D code would have exactly the same structure.

It would also give me a chance to improve my D, which is sorely needed.

I started out debugging the state machine and getting it right, using AWK. I then ported the AWK to the iOS Shortcuts language is that now I have the preprocessor tool running in my iPad too. iOS Shortcuts is such a nightmare and you can easily get lost so having something already thought out, which you can just follow robotically, really helps.

I have got Python for the iPad but I wouldnít even know where to start. It looks incredibly powerful.
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