Advance I/O redirection in bash. /dev/null

devnull.txt

For those unfamiliar with 'advanced' i/o redirection in bash: 
1) 2>&- ("close output file descriptor 2", which is stderr) has the same result as 2> /dev/null; 
2) >&2 is a shortcut for 1>&2, which you may recognize as "redirect stdout to stderr". 

See the Advanced Bash Scripting Guide i/o redirection page for more info. 
– mikewaters Dec 21 '11 at 19:48 
-comment from : https://stackoverflow.com/questions/592620/check-if-a-program-exists-from-a-bash-script

sometimes 7 year old comments on Stack Overflow are still very useful =)