Q:

grep two strings from a file and write into a txt

Could you please help me how to grep two strings (or the whole lines) from one file and write them on the same line in output file? 
grep -e "string1 string2" inputfile > output.txt doesn't work

for one string it works: 
grep -e "string1" inputfile > output.txt 

thx!

A:

Change your grep command like below,
grep -o 'string1\|string2' file | paste - - > out.txt

This writes string1 string2 in a single line on out.txt

