Aliases and Awk

Conversation started Nov 13, 2011 at 17:48.

Iszi

Nov 13, 2011 17:48

@ScottPack Was going to ask something about passing parameters through aliases, but Google tells me it's not doable.

Ended up figuring another way to get what I wanted out of the alias, and then some, without doing that anyway.

Scott Pack

Nov 13, 2011 18:07

Yeah, your best option is to just write a function

Iszi

I went with an alias that got me a bit more information than I was wanting, but with a name that reflects that. So, it's not so bad.

alias myips="ifconfig | grep 'inet addr' | cut -d ':' -f2 | cut -d ' ' -f1"

Scott Pack

Iszi

@ScottPack What's "ew"? a five-letter alias that lists all the IPv4 addresses on the box?

(without any other fluff)

Scott Pack

It just looks nasty.

Iszi

@ScottPack I'm sure I could've done plenty worse.

Scott Pack

Nov 13, 2011 18:19

Well, that's weird. The man page for ifconfig on Fedora 15 says that it's obsolete

Iszi

What, you were hoping to find a less-emo way to do it?

Scott Pack

I was starting to work on cleaning it up, when I noticed that.

Do you care about v6?

Iszi

@ScottPack Not really at this point

Scott Pack

ip addr | awk '/inet / {print $2}'

Bam!

Iszi

Hence my use of grep 'inet addr' instead of just grep inet

Oh hey! CIDR subnet masks with that one, too!

Scott Pack

Nov 13, 2011 18:22

Yeah, I thought that was nice too.

Iszi

Didn't know about the ip addr command, and I'm only barely aware of awk.

Scott Pack

Change that to '/inet/ to get the ipv6 addresses as well.

Iszi

So... let me make sure I'm reading this right...

Scott Pack

I ended up learning awk instead of cut. Which worked out to be nice later on when I realized that most of the time I was just piping grep into awk.

So by putting the regex directly into awk it removed a step.

Iszi

You're running the ip addr command and passing it to awk obviously.

Then, awk looks for "inet " and prints the second word off of that line?

@ScottPack Ah, but that means learning regexes. I'm not quite to that level yet.

Scott Pack

Nov 13, 2011 18:26

More specifically, prints the second field where space is the default field delimiter, but yeah.

Iszi

@ScottPack By "default" I presume you mean that's alterable?

Scott Pack

While /inet / is technically a regex, from a practical standpoint it's just a string.

Indeed.

So, let's re-write that to use ifconfig.

Iszi

So, if I really didn't care about the CIDR, I'd tell awk to use ":" as a delimiter and run ifconfig instead.

Scott Pack

ifconfig | awk '/inet addr/ {print $2}' | awk -F: '{print $2}'

Iszi

@ScottPack That... doesn't look right.

Scott Pack

Nov 13, 2011 18:29

Which part?

Iszi

I mean, it obviously works...

It just seems that one of those awks is superfluous.

Scott Pack

So you're thinking that you can just split on ':' on the first one?

Iszi

@ScottPack It would seem you should be able to.

Scott Pack

You can only split on one string at a time

So, move the -F: to the first one and see what happens

Iszi

@ScottPack Yeah, that was... odd. I think there may be some order to the parameters.

And that was even weirder.

First I tried ifconfig | awk '/inet addr/ -F: '{print $2}'. That dropped me to some sort of blank command prompt.

Scott Pack

Nov 13, 2011 18:35

Well, you got two problems there

Let me back up.

awk is a programming language used for text processing.

Iszi

I tried ifconfig | awk -F: '/inet addr/ {print $2}' and it gave me the IP and the next word.

Scott Pack

So, the line, /inet addr/ {print $2} is really just code that awk is interpreting.

Iszi

Apparently, when you set a delimiter, it's ignoring the default delimiter altogether.

Scott Pack

The -F is an argument to the application itself, not part of the code.

Right, you're changing the delimiter.

Iszi

So, can you specify multiple delimiters?

Scott Pack

Nov 13, 2011 18:37

The blank command line you got is part of bash, not awk.

@Iszi To the best of my knowledge no.

There are thousands, of people out there that know way more about awk than I do. So if one of them shows me how, I'll change my mind.

Chore time. Gotta run

Check out this page

pement.org/awk/awk1line.txt

It could be way over your head right now, or it could help you learn the kinds of things you can do.

Conversation ended Nov 13, 2011 at 18:39.

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