'+' (one or more occurrences) not working with 'sed' command

Question

I'm trying to refine my code by getting rid of unnecessary white spaces, empty lines, and having parentheses balanced with a space in between them, so:

    int a = 4;     if ((a==4) ||   (b==5))      a++   ; 

should change to:

    int a = 4;     if ( (a==4) || (b==5) )     a++ ; 

It does work for the brackets and empty lines. However, it forgets to reduce the multiple spaces to one space:

    int a = 4;     if ( (a==4) ||   (b==5) )     a++    ; 

Here is my script:

    #!/bin/bash     # Script to refine code     #     filename=read.txt      sed 's/((/( (/g' $filename > new.txt     mv new.txt $filename      sed 's/))/) )/g' $filename > new.txt     mv new.txt $filename      sed 's/ +/ /g' $filename > new.txt     mv new.txt $filename      sed '/^$/d' $filename > new.txt     mv new.txt $filename 

Also, is there a way to make this script more concise, e.g. removing or reducing the number of commands?

Answer 1

If you are using GNU sed then you need to use sed -r which forces sed to use extended regular expressions, including the wanted behavior of +. See man sed:

-r, --regexp-extended         use extended regular expressions in the script. 

The same holds if you are using OS X sed, but then you need to use sed -E:

-E      Interpret regular expressions as extended (modern) regular expressions         rather than basic regular regular expressions (BRE's).