List only Red Hat satellite child channel,per base channel

Question

I am writing bash script to replicate channels from one satellite to another.

I want to get only the list of child channels for the base channel: clone-rhel-x86_64-server.

I have intentionally used grep -E -A10 to give the option output of up to 10 child channels.

Right now I am getting:

rhn-satellite-exporter --list-channels |grep -E -A10 '(^| )clone-rhel-x86_64-server( |$)'|grep  -v "^B"
C       child_channel1
C       child_channel2
C       child_channel3

C       child_channel4
C       child_channel5
C       child_channel7

My purpose is go get only the first section, ie only the child channels.

For base channel: clone-rhel-x86_64-server

rhn-satellite-exporter --list-channels |grep -E -A10 '(^| )clone-rhel-x86_64-server( |$)'|grep  -v "^B"
C       child_channel1
C       child_channel2
C       child_channel3

How do I achieve that?

Answer 1

One way to do this would be to use perl 's paragraph mode. From man perlrun :

   -0[octal/hexadecimal]
        specifies the input record separator ($/) as an octal or
        hexadecimal number. [. . .]
        The special value 00 will cause Perl to slurp files in paragraph
        mode.  [. . .]

In paragraph mode, "lines" are defined by \\n\\n and not \\n alone, so each "line" is actually a paragraph. You can therefore use a Perl one-liner and tell it to print the first line and exit:

rhn-satellite-exporter --list-channels |
    grep -E -A10 '(^| )clone-rhel-x86_64-server( |$)'| grep  -v "^B" |
        perl -00ne 'print;exit'

Note that the above will also print the empty line since that is considered part of the paragraph. To avoid that, you could either parse it out:

 rhn-satellite-exporter --list-channels |
    grep -E -A10 '(^| )clone-rhel-x86_64-server( |$)'| grep  -v "^B" |
        perl -00ne 'print;exit' | grep .

Or remove it in the Perl script itself:

 rhn-satellite-exporter --list-channels |
    grep -E -A10 '(^| )clone-rhel-x86_64-server( |$)'| grep  -v "^B" |
        perl -00ne 's/\n\s*\n/\n/;print;exit' | grep .