The Quick Answer
- -O flag is the short notation for the flag --output-document in wget command-line utility.
- The hypen - after the flag denotes STDOUT.
Thus, wget -O- www.codonomics.com or wget -O - www.codonomics.com prints the result returned from that URL in your terminal output or STDOUT.
Learn By Example
- wget -O www.codonomics.com writes the output to index.html file
- wget -O custom.txt www.codonomics.com writes the output to your custom.txt file as mentioned
- wget -O - www.codonomics.com writes output to your terminal's STDOUT