3. Exit Codes & Data Stream

echo $? will tell the exit code of the last command

• exit code of 0 indicate the program is successful
• $? will only get exit code of the last command, need to use it before echo
exit command in a bash script will force exit a program and everything after it will not run

set -e will exit the script on error
set +e will do the opposite, reset the option of set -e

Data Streams
stdout standard output: output that is printed to the screen that doesn’t result in an error
stderr standard error: stout that is returning failed. eg. permission denied, file not found
stdin standard input: what the user inputs

• read command is used to ask user for stdin

read -p "what's your name: " yourname && echo "Hello $myname"

• -p option allows for a prompt eg. what’s your name
• the stdin is stored in a variable yourname

DS Redirection
> is used to redirect streams
>> is for appending streams
2> /dev/null will send stderr into dev null, which will hide the stderr message

• 2 is error
• 1 is stdout, not error
• by default > only redirect stdout (1), if number not given, 1 is implied
  &> target will redirect both stdout and stderr to the target
• & indicates both 1 and 2
  Redirection can be separated

find /etc -type f 1>stdout.txt 2>stderr.txt

• this command will redirect stdout and stderr to different locations separately