
\S exit status:  return code:  false:  true \S

Every command returns an integer to the shell when it terminates. This
integer is called the exit status or return code and it indicates what
happened when the command was executed.  If it is "true" that the command
executed successfully, the command returns an exit code of zero.  Zero
means that the command executed with zero problems.  If it is "false" that
the command executed successfully, the command returns a non-zero integer.
This integer represents the type of problem that caused the command to
fail.  For example, the command grep(1) returns an exit status of 1 if the
command failed because there was no pattern that matched the pattern you
gave on the command line. grep(1) returns an exit status of 2 if the
command failed because you made an error in the pattern or if you used file
names that did not exist. You can find out what the exit status of your
last command is by typing "echo $?" immediately after the command finishes
executing.  Exit status is used most often in shell programs.

