$s = << __END;
random overhead
[ oracle\@ipda04 ] \$ hostname
ipda04</ IA%EXAMPLE >
text here
[ source]
anything here
< IA
%COMMAND > stuff to
print </ IA
%COMMAND > < IA%xxx > test</ IA%xxx >
stuff that should be ignored
[ oracle\@ipda04 ] \$ hostname
ipda04</ IA%EXAMPLE >
text here
[ target]
< IA%UICOMMAND > other stuff to print</ IA%UICOMMAND >
stuff to be ignored
[ target]
< IA
%COMMAND > print out this too
and this as well </ IA%COMMAND >
__END
$s =~ s/(?:\A.*?(?=^\[[^[\]]*\](?:\n|\z)|\z)|(?<=[>\]]\n)(?!\[[^[\]]*\]*(?:\n|\z)|<[^>]*COMMAND>).*?(?=^\[[^[\]]*\](?:\n|\z)|^<[^>]*COMMAND>|\z))//gms ;
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