Collapsing a stream of multiple lines into one line

Question

I have a file containing a a large number of lines, each of which contains a bunch of numbers which are separated by spaces. I process this data in a pipe in some way, and then I want to collapse the multiple lines into a single line of all the numbers separated by spaces.

Is there a standard command-line utility I can use to do this? It seems like most line-by-line utilities won't mess with the newlines...

Answer 1

That's why you don't use line-by-line utilities for this.

$ tr '\n' ' ' < input.txt > output.txt

Answer 2

Even line-by-line utilities can remove all newlines.

sed:

sed ':a;N;$!ba;s/\n/ /g' file

awk:

awk '{printf $0" "}' file

But it's much better to use tr, like @Ignacio Vazquez-Abrams wrote.