请教个问题，请各位不吝赐教

代码:

#!/bin/sed -nf

     # Prime the pump on the first line
     x
     /^$/ s/^.*$/1/
   

     # Add the correct line number before the pattern
     G
     h

     # Format it and print it
     s/^/      /
     s/^ *\(......\)\n/\1  /p

     # Get the line number from hold space; add a zero
     # if we're going to add a digit on the next line
     g
     s/\n.*$//
     /^9*$/ s/^/0/

     # separate changing/unchanged digits with an x
     s/.9*$/x&/

     # keep changing digits in hold space
     h
     s/^.*x//
     y/0123456789/1234567890/
     x

     # keep unchanged digits in pattern space
     s/x.*$//
     # compose the new number, remove the newline implicitly added by G
     G
     s/\n//
     h

引用:

/^$/ s/^.*$/1/