# Some basic redirection
% ls -l  # stdout is printed to the terminal
% ls -l > /tmp/ls-l.txt  # stdout is redirected to a file
% > /tmp/ls-la.txt ls -la  # stdout is redirected to a file (order doesn't matter)
% ls -M  # stderr is printed to the terminal
ls: invalid option -- 'M'
Try 'ls --help' for more information.
% ls -M 2>&1 | grep 'invalid'  # stderr is redirected to stdout
ls: invalid option -- 'M'
% ls -M 2> /dev/null  # stderr is sent to a blackhole (i.e. ignore all errors)

# Some intermediate redirection
% for i in {1..5}; do date >> /tmp/timestamps; sleep 5; done  # append output to file
% for i in {1..5}; do date | tee /tmp/timestamps; sleep 1; done  # split stdout to file and terminal
% brew list --formula -1 > /tmp/brew-list  # output a list of installed packages
% while read -r formula; do brew info $formula; done < /tmp/brew-list  # stdin is a file
% while read -r formula; do brew info $formula; done <<< "$(brew list --formula -1)"  # stdin is a command
% docker image prune -f > /dev/null 2>&1  # redirect stderr to stdout and redirect stdout to /dev/null (i.e. ignore everthing)

# Using redirection instead of pipes
% tr ' ' '\n' <<< "$(id -Gn)"
% sed 's/Fri/Friday/' < /tmp/timestamps

# Using process substitution
% diff <(sort file1) <(sort file2)  # the output of a command appears as a file