How do I pair every two lines of a text file with Bash? [duplicate]

Question

With a simple bash script I generate a text file with many lines like this:

192.168.1.1
hostname1
192.168.1.2
hostname2
192.168.1.3
hostname3

Now I want to reformat this file so it looks like this:

192.168.1.1 hostname1
192.168.1.2 hostname2
192.168.1.3 hostname3

How would I reformat it this way? Perhaps sed?

Answer 1

$ sed '$!N;s/\n/ /' infile 192.168.1.1 hostname1 192.168.1.2 hostname2 192.168.1.3 hostname3 

Answer 2

I love the simplicity of this solution

cat infile | paste -sd ' \n'

192.168.1.1 hostname1
192.168.1.2 hostname2
192.168.1.3 hostname3

or make it comma separated instead of space separated

cat infile | paste -sd ',\n'

and if your input file had a third line like timestamp

192.168.1.1
hostname1
14423289909
192.168.1.2
hostname2
14423289910
192.168.1.3
hostname3
14423289911

then the only change is to add another space in to the delimiter list

cat infile | paste -sd '  \n'

192.168.1.1 hostname1 14423289909
192.168.1.2 hostname2 14423289910
192.168.1.3 hostname3 14423289911

Answer 3

Here's a shell-only alternative:

while read first; do read second; echo "$first $second"; done