Remove unnecessary blank lines

Question

Let's imagine that the following code example is valid:

begin
   statement1;

   begin


      statement2;

      statement3;
      statement4;

      statement5;

   end;

   statement6;

end;

I would like to remove all unnecessary blank lines in this code example:

begin
   statement1;

   begin
      statement2;

      statement3;
      statement4;

      statement5;
   end;

   statement6;
end;

So basically if a line ends with the keyword begin then all blank lines until the next line that contains a statement should be removed and if a line ends with the keyword end; then all blank lines until the previous line that contains a statement should be removed.

Using Sublime Text I created two regular expressions:

1. Find: begin(\\n)* and Replace: begin\\n
2. Find: (\\n)*([[:space:]])*end; and Replace: \\nend;

My questions:

1. How can I convert both regular expression so that they can be used with sed (in-place)?
2. The second regular expression drops all existing blank spaces before the keyword end; . How could this problem be fixed?

Answer 1

With GNU sed 4.2 you have the option -z :

sed -rz 's/begin\n+/begin\n/g;s/\n+([^\n]*end;)/\n\1/g' file

Work-around with older sed (when original file is without \\r )

tr '\n' '\r' < file | sed -r 's/begin\r+/begin\r/g;s/\r+([^\r]*end;)/\r\1/g' | tr '\r' '\n'

Answer 2

Not the most elegant solution, but I'll continue trying this one :)

cat file | awk '
length { print; b=0 }
/begin/ { b=1 }
/^$/ && b { next }
!length && !b { print }
' | tac | awk '
length { print; b=0 }
/end;/ { b=1 }
/^$/ && b { next }
!length && !b { print }
' | tac 

I'm running the same awk , but I invert the file for the end; part ( tac ).

Explanation of the awk :

1. If the line is not empty ( length ), print it and set b to 0 (false)
2. If the line starts with the string begin (ignoring blank chars [ \\s ]), set b to 1 (true)
3. If the line is blank ( ^$ ), and b is true (we're 1 line after begin ), skip this line ( next )
4. If the line is blank and we're not after begin , print (because we don't want to eliminate all blank lines)