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

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?

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).

You have to preceed + with a \, otherwise sed tries to match the character + itself.

To make the script "smarter", you can accumulate all the expressions in one sed:

sed -e 's/((/( (/g' -e 's/))/) )/g' -e 's/ \+/ /g' -e '/^$/d' $filename > new.txt

Some implementations of sed even support the -i option that enables changing the file in place.

Sometimes, -r and -e won't work. I'm using sed version 4.2.1 and they aren't working for me at all.

A quick hack is to use the * operator instead. So let's say we want to replace all redundant space characters with a single space: We'd like to do:

sed 's/ +/ /'

But we can use this instead:

sed 's/  */ /'

(note the double-space)

May not be the cleanest solution. But if you want to avoid -E and -r to remain compatible with both versions of sed, you can do a repeat character cc* - that's 1 c then 0 or more c's == 1 or more c's.

Or just use the BRE syntax, as suggested by @cdarke, to match a specific number or patternsc\{1,\}. The second number after the comma is excluded to mean 1 or more.

This might work for you:

sed -e '/^$/d' -e ':a' -e 's/\([()]\)\1/\1 \1/g' -e 'ta' -e 's/  */ /g' $filename >new.txt

on the bash front;

First I made a script test.sh

cat test.sh

#!/bin/bash
while IFS='' read -r line || [[ -n "$line" ]]; do
    echo "Text read from file: $line"
	SRC=`echo $line | awk '{print $1}'`
	DEST=`echo $line | awk '{print $2}'`
	echo "moving $SRC to $DEST"
	mv $SRC $DEST || echo "move $SRC to $DEST failed" && exit 1
done < "$1"

then we make a data file and a test file aaa.txt

cat aaa.txt
<tag1>19</tag1>
<tag2>2</tag2>
<tag3>-12</tag3>
<tag4>37</tag4>
<tag5>-41</tag5>

then test and show results.

bash test.sh list.txt 
Text read from file: aaa.txt bbb.txt
moving aaa.txt to bbb.txt