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

bash, macos, sed

Solution

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).

Problem

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?

Original source