Shell scripting: enclose all lines with quotes

• Using awk:

  awk '{print "\""$0"\""}' input.txt
  

  or if ignore empty lines:

  awk 'NF {print "\""$0"\""}' input.txt
  

• Or using sed:

  sed -i.bak 's/^/"/; s/$/"/' input.txt
  

  or if ignore empty lines:

  sed -i.bak 's/^..*$/"&"/' input.txt