How to concatenate multiple lines of output to one line?

Question

If I run the command cat file | grep pattern, I get many lines of output. How do you concatenate all lines into one line, effectively replacing each \"\\n

Answer 1

Here is another simple method using awk:

# cat > file.txt
a
b
c

# cat file.txt | awk '{ printf("%s ", $0) }'
a b c

Also, if your file has columns, this gives an easy way to concatenate only certain columns:

# cat > cols.txt
a b c
d e f

# cat cols.txt | awk '{ printf("%s ", $2) }'
b e