Korn Shell: Unix and Linux Programming Manual, Third Edition, The

Special Parameters

Some special parameters are automatically set by the Korn shell and usually cannot be directly set or modified.

The ? Parameter

The ? parameter contains the exit status of the last executed command. In this example, the date command is executed. It ran successfully, so the exit status is 0:

						$ date +%D
						05/24/96
						$ print $?
						0
					

Notice that there was no output displayed from the date command. This is because the >&– I/O operator causes standard output to be closed. The next command, cp ch222.out /tmp, did not run successfully, so 1 is returned:

						$ cp ch222.out /tmp
						ch222.out: No such file or directory
						$ print $?
						1
					

When used with a pipe, $? contains the exit status of the last command in the pipeline.

Table 3.4. Some Preset Special ...