Bourne Shell Exit Status Examples

Can you explains and provide us "Bourne Shell Exit Status Code" examples?

Each UNIX command returns a status when it terminates. If it is not successful, it returns a code which tells the shell to print an error message. You can use the
exit command to leave a shell program with a certain exit status.

Typical Values Of Exit Status

• 0 Success.
• 1 A built-in command failure.
• 2 A syntax error has occurred.
• 3 Signal received that is not trapped.

How Do I Print Exit Status?

Type the command:
$ ls
To print its exit status type the command:
$ echo $?
Try a few more examples:
date1
echo $?
date
echo $?
cat /etc/passwd
echo $?
To store exit status of the last executed command to a shell variable called status, enter:
command1
status=$?
You can use exit status with test command or if command too.

#!/bin/sh
user="$1"
if grep "$user" /etc/passwd; then
        echo "$user has an account"
else
        echo "$user doesn't have an account"
fi

Run it as follows:
./script-name vivek
The grep command is used as condition but it can actually be any command. If it returns a zero exit status, the condition is true; otherwise, it is false. In this example, the while loop executes given commands as long as condition is true. Again, condition can be any command, and is true if the command exits with a zero exit status.

 
while condition; do
        commands
done
 

Here is another simple example:

#!/bin/sh
x=0
while [ $x != 3 ]
do
     let x=x+1
    echo $x
done

Here is another example:

#!/bin/sh
while [ -r "$1" ]
do
    cat $1 >> output
    shift
done

Run it as follows:
./script-name file1 file2 fil3
cat output