STDIN and ATDOUT Bash
Diagram Process
stdin->process->stdout
1.Stdin (Input)
stdin 0 Read input from a file
example :
cat < file
2. Stdout (Output)
stdout 1 Send data to a file (write).
example :
date > output.txt
cat output.txt
3. Stderr(Process)
Stderr 2 Send all error messages in default screen to a file. usually error message when porcess take place.
example :
rm /tmp/test.txt 2> error.txt
cat error.txt
How to direct ouput unwanted?
error message usually there on default screen, if we don’t want error message or message view on screen terminal, we get to throw to device file unix like on /dev/null or /dev/zero
example :
1. remove error message on view
command 2>/dev/null
2. remove message output on view
command >/dev/null
DIrections EOF (End Of File)
Example :
wc -w <<EOF
> This is a test.
> Apple juice.
> 100% fruit juice and no added sugar, colour or preservative.
> EOF
Direction read string
Example :
wc -w <<<“coba test”
grep galuh <<<“galuh tampan sekali”
Direction with other File Descriptor
exec 3< /etc/resolv.conf
cat <&3
output : nameserver 192.168.42.129
remove directions
exec 3<&-
cat <&3
ouput : zsh: 3: bad file descriptor