stderr and stdout redirections

stderr_stdout_redirection.sh

#    redirect stdout to a file
cat 1.txt > r.txt

#    redirect stderr to a file
grep "error" 1.log 2> r.txt 

#    redirect stdout to a stderr
grep * 1>&2

#    redirect stderr to a stdout
grep * 2>&1

#    redirect stderr and stdout to a file (often used in cron job)
grep * &> /dev/null