Error checking

Almost every system call or library routine can, somehow, encounter an error during its operation. While many of these occur only because of programmer error, each such problem indicates a failure of either the system, the calling program or a transient parameter like access permission or available memory. If a programmer chooses to ignore a reported error, the result is a command that, should some basic assumption of the system fail, could corrupt its environment. For trusted commands, therefore, every possible error return must be checked and reported. This rule is not always followed to the letter, since in some cases it is more efficient to detect the error case downstream from the actual failure. Ignoring errors is risky and should not be done without strong justification.