I have a following data:

100 200
300 400

I want the data to be arranged:

100 200 300 400

What is the best way to do this?

Thanks!

Please search the forums before asking (per the rules, thanks):

Shell script to join a line to the line that follows it

So many examples in the database on this topic.

I tried this already and it doen't work. Please reply with solution not a run-around!!!

many thanks!

You may not realize it, but your reply puts you about 4 mouse click from being banned :-)

Please do define 'it' and describe the 'not working' part.
What exactly have you tried and what exactly has not worked?

probably easier ways but...

cat << EOF |
100 200
300 400
500 600
700 800
900 1000
EOF

  awk '{
    printf( "%s ", $0 );
    if ( NR % 2 == 0 ){
      printf( "\n" );
      }
    }
    END{
      printf( "\n" );
    }'

100 200 300 400
500 600 700 800
900 1000