Error handling in unix shell ksh - unix

Question

Can anyone guide to a document or explain on the below
how to use error handling in ksh.
How does Unix work on unhandled errors(like error happened in the
subscript etc..).

Answer 1

From ksh man page.
Unhandled errors
Errors detected by the shell, such as syntax errors, cause the shell to return a non-zero exit status. If the shell is being used
non-interactively, then execution of the shell
file is abandoned UNLESS the error occurs inside a subshell in which case the subshell is abandoned.
Error handling
Basically check exit/return codes to handle errors:
if [ $exit_code != 0 ]; then
# Your error handler
fi
Example
test_handler() {
ls file_not_present
if [ $? -eq 2 ]; then
echo "Handler for No such file or directory"
elif [ $? -ne 0]; then
echo "Handler for any other exception"
else
echo "Succesful execution"
fi
}
Will throw:
ls: cannot access non_file: No such file or directory
Handler for No such file or directory
But if the command does not exit:
test_handler() {
l file_not_present
if [ $? -eq 2 ]; then
echo "Handler for No such file or directory"
elif [ $? -ne 0 ]; then
echo "Handler for any other exception"
else
echo "Succesful execution"
fi
}
The output will be:
l: not found [No such file or directory]
Handler for any other exception
The shell returns
the exit status of the last command executed
(see also the exit command above). Run time errors detected by the shell are reported by printing the command or function name and
the error condition. If the line number that
the error occurred on is greater than one, then the line number is also printed in square brackets ([]) after the command or function
name.