open my $lookup, '<', $lookuptxtfile or die $!;
open my $new_lookup, '>', "$lookuptxtfile.new" or die $!;
while (<$lookup>) {
    s/The action failed./failed_build/g;
    print {$new_lookup} $_;
}
close $new_lookup;
rename "$lookuptxtfile.new", $lookuptxtfile or die $!;
[download]

Creating a new file and renaming it is what sed does behind the scenes, anyway.

Are you sure you don't want to backslash the dot?

($q=q:Sq=~/;[c](.)(.)/;chr(-||-|5+lengthSq)`"S|oS2"`map{chr |+ord
}map{substrSq`S_+|`|}3E|-|`7**2-3:)=~y+S|`+$1,++print+eval$q,q,a,
[download]