Emulating ‘cat -b’ is almost the same as ‘cat -n’—we only have to select which lines are to be numbered and which are not.
The part that is common to this script and the previous one is
not commented to show how important it is to comment sed
scripts properly...
#!/usr/bin/sed -nf
/^$/ {
p
b
}
# Same as cat -n from now x /^$/ s/^.*$/1/ G h s/^/ / s/^ *\(......\)\n/\1 /p x s/\n.*$// /^9*$/ s/^/0/ s/.9*$/x&/ h s/^.*x// y/0123456789/1234567890/ x s/x.*$// G s/\n// h