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Full Discussion: awk - remove block of text, multiple actions for 'if', inline edit
Top Forums UNIX for Advanced & Expert Users awk - remove block of text, multiple actions for 'if', inline edit Post 302466600 by mglenney on Tuesday 26th of October 2010 07:30:11 PM
Old 10-26-2010
Quote:
Originally Posted by agama
Use curly braces to group a set of statements to execute when the expression evaluates to true:
Ok, thanks. That was making me nuts.

Quote:
[code]
awk -v remove=XMPP_ec2-184-2-2-2 '
/define host/ { # start of new block; print last section
if( snarfed )
print snarfed;

snarfed = $0; # start capture
next;
}

/host_name/ { # check to see if unwanted target
if( $2 == remove ) # if it is then
snarfed = ""; # unset to trash the whole block
next;
}
snarfed { # if we are snarfing from current section
snarfed = snarfed "\n" $0; # add next line
next;
}
END { # must do one last for the last buffered section
if( snarfed )
print snarfed;
}
' config-file
Cool. I knew there was a way to do this without 2 awk statements. What you wrote here is almost what I need. It was removing the "host_name" record from all the host definitions so I removed the "next;" line from the /host_name/ section.

Your comment about other text in the file made me realize I need to support that. I added in some text and any text before the first "define host" is not output. Here's the test file:

Code:
$ cat testdata.cfg 
This is some text
#this is some commented text

define host{
    use        linux-server,host-pnp
    host_name    XMPP_ec2-184-1-1-1
    alias        XMPP_ec2-184-1-1-1
    address        ip-10-10-10-10.us-west-1.compute.internal
    }

define host{
    use        linux-server,host-pnp
    host_name    XMPP_ec2-184-2-2-2
    alias        XMPP_ec2-184-2-2-2
    address        ip-10-20-20-20.us-west-1.compute.internal
    }

define host{
    use        linux-server,host-pnp
    host_name    XMPP_ec2-204-1-1-1
    alias        XMPP_ec2-204-1-1-1
    address        ip-10-30-30-30.us-west-1.compute.internal
    }

This is some after text

And this is the awk:
Code:
 awk -v remove=XMPP_ec2-184-2-2-2 '
        /define host/ {
                if( snarfed )
                        print snarfed;

                snarfed = $0;
                next;
        }

        /host_name/ {
                if( $2 == remove )
                        snarfed = "";
        }
        snarfed {
                snarfed = snarfed "\n" $0;
                next;
        }
        END {
                if( snarfed )
                        print snarfed;
        }
' testdata.cfg

and this is the result:
Code:
define host{
    use        linux-server,host-pnp
    host_name    XMPP_ec2-184-1-1-1
    alias        XMPP_ec2-184-1-1-1
    address        ip-10-10-10-10.us-west-1.compute.internal
    }

define host{
    use        linux-server,host-pnp
    host_name    XMPP_ec2-204-1-1-1
    alias        XMPP_ec2-204-1-1-1
    address        ip-10-30-30-30.us-west-1.compute.internal
    }

This is some after text

  1. Any idea why the text before the first host definition gets snipped?
  2. How does this work? Is 'snarfed' a function?
 

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