remove new line if next line does not begin with a number

Question

I have a file that is like

    1 test
    test

How can I remove the new line from the so the final output becomes:

1 test test

Answer 1

A solution using 'sed':

Input file (infile):

1 test
test
2 two 
3 three
4 four
five 
six
7 seven
eight
9 nine

'Sed' program (script.sed):

/[0-9]\+/ {
        : a 
        N
        /\n[0-9]\+/ {
                P
                s/.*\n//
        }
        t a
}

y/\n/ /

Execution:

$ sed -f script.sed infile

Output:

1 test test
2 two
3 three
4 four five 
six
7 seven eight
9 nine