Comments on: Squawk (simple queues using awk) http://www.nobugs.org/blog/archives/2008/05/11/squawk-simple-queues-using-awk/ Thoughts of a software engineer Thu, 11 Mar 2010 02:14:40 +0000 http://wordpress.org/?v=2.8.4 hourly 1 By: Andrew http://www.nobugs.org/blog/archives/2008/05/11/squawk-simple-queues-using-awk/comment-page-1/#comment-33393 Andrew Wed, 14 May 2008 11:37:24 +0000 http://www.nobugs.org/blog/archives/2008/05/11/squawk-simple-queues-using-awk/#comment-33393 Ken: Yep, that works fine if you are using netcat as a data source and filtering its output with awk. But for squawk I also need the output from awk to be fed back into netcat's stdin - its a two way conversation. I use netcat -c "my_awk_command" for this. But that means my awk command invocation would need to be escaped otherwise bash will expand things like '$0' which I intend for awk. Hmm, actually, I think in this case I can surround the awk invocation with single quotes and then consistently use double quotes within the awk script. In an earlier version I was relying on the awk script being bash-expanded to do variable substitution for the queue name. But now I explicitly pass the arguments in with --assign. Ah, no .. I still need to shell-expand the --assign part of the awk invocation, so it can't be in single quotes. This page has some suggestions; I'll see if I can get it to work: http://www.gnu.org/manual/gawk/html_node/Quoting.html. I didn't know that if you run something like this: ls 'foo'"bar" (no space between the quotes) .. then ls receives a single argument - I'd always assumed it'd get two arguments. Ken: Yep, that works fine if you are using netcat as a data source and filtering its output with awk. But for squawk I also need the output from awk to be fed back into netcat’s stdin – its a two way conversation. I use netcat -c “my_awk_command” for this. But that means my awk command invocation would need to be escaped otherwise bash will expand things like ‘$0′ which I intend for awk.

Hmm, actually, I think in this case I can surround the awk invocation with single quotes and then consistently use double quotes within the awk script. In an earlier version I was relying on the awk script being bash-expanded to do variable substitution for the queue name. But now I explicitly pass the arguments in with –assign.

Ah, no .. I still need to shell-expand the –assign part of the awk invocation, so it can’t be in single quotes.

This page has some suggestions; I’ll see if I can get it to work: http://www.gnu.org/manual/gawk/html_node/Quoting.html. I didn’t know that if you run something like this:

ls ‘foo’”bar” (no space between the quotes)

.. then ls receives a single argument – I’d always assumed it’d get two arguments.

]]> By: ken horn http://www.nobugs.org/blog/archives/2008/05/11/squawk-simple-queues-using-awk/comment-page-1/#comment-33390 ken horn Wed, 14 May 2008 10:11:41 +0000 http://www.nobugs.org/blog/archives/2008/05/11/squawk-simple-queues-using-awk/#comment-33390 you can get away with this: #! /bin/bash (echo "GET / HTTP/1.0" ; echo "") | nc www.yahoo.com 80 | awk ' BEGIN{ i=0 } { print i++ "> " $0; }' | head -20 alternatively if you need more processing, use " instead or you can even process the current file and pipe it to awk if stdin is spare (i've used ## comments to give a grep target), using back ticks to get extra nested shells is a neat trick too.. you can get away with this:
#! /bin/bash

(echo “GET / HTTP/1.0″ ; echo “”) | nc http://www.yahoo.com 80 | awk ‘
BEGIN{
i=0
}
{
print i++ “> ” $0;
}’ | head -20

alternatively if you need more processing, use ” instead or you can even process the current file and pipe it to awk if stdin is spare (i’ve used ## comments to give a grep target), using back ticks to get extra nested shells is a neat trick too..

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