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18:23 >perl -wE "my $s = qq[abc\n\t \ndef\n \ngh]; $s =~ s/^\s*$/X/m +g; say $s;" abc ... gh 18:24 >
18:24 >perl -wE "my $s = qq[abc\n\t \nd\tef\n \ngh]; $s =~ s/[ \t]+/ +X/mg; say $s;" abc ... gh 18:39 >