Concatenate Lines in Bash

Question

Most command-line programs just operate on one line at a time.

Can I use a common command-line utility (echo, sed, awk, etc) to concatenate every set of two lines, or would I need to write a script/program from scratch to do this?

$ cat myFile
line 1
line 2
line 3
line 4

$ cat myFile | __somecommand__
line 1line 2
line 3line 4

Answer 1

sed 'N;s/\n/ /;'

Grab next line, and substitute newline character with space.

seq 1 6 | sed 'N;s/\n/ /;'
1 2
3 4
5 6

Answer 2

$ awk 'ORS=(NR%2)?" ":"\n"' file
line 1 line 2
line 3 line 4

$ paste - -  < file
line 1  line 2
line 3  line 4

Answer 3

Not a particular command, but this snippet of shell should do the trick:

cat myFile | while read line; do echo -n $line; [ "${i}" ] && echo && i= || i=1 ; done

Answer 4

You can also use Perl as:

$ perl -pe 'chomp;$i++;unless($i%2){$_.="\n"};' < file
line 1line 2
line 3line 4