Why the exit status of a program is important, continued
Most operating system shells are, themselves,
programming languages,
and they may use a program's exit status to direct control-flow
within the shells - thus, the programming language that is the shell,
is treating your programs as if they are external functions.
Shells are typically programmed using files of commands named
shellscripts or command files
and these will often have conditional constructs,
such as if and while, just like C.
It's thus important for our programs to work with the shells that invoke them.
We now compile our program, and invoke it with combinations of zero,
and non-zero arguments:
prompt> mycc -o status status.c
prompt> ./status 0 && ./status 1
exiting(0)
exiting(1)
prompt> ./status 1 && ./status 0
exiting(1)
prompt> ./status 0 || ./status 1
exiting(0)
prompt> ./status 1 || ./status 0
exiting(1)
exiting(0)
|
- Example1 - consider the sequence
prompt> cd mydirectory && rm -f *
- Example2 - consider the actions in a Makefile
(discussed in a later lecture).
If a target has more than one action,
then the make program executes each until one of them fails
(or until all succeed).
CITS2002 Systems Programming, Lecture 9, p8, 21st August 2023.
|
CITS2002