Creating a target file with the make command

To create a file containing the completed program called a target file, the make program:

1. Finds the name of the target file in the description file or in the make command
2. Ensures that the files on which the target file depends exist and are up-to-date
3. Determines if the target file is up-to-date with the files on which it depends.

If the target file or one of the parent files is out-of-date, the make command creates the target file using one of the following:

• Commands from the description file
• Internal rules to create the file (if they apply)
• Default rules from the description file

If all files in the procedure are up-to-date when running the make program, the make command displays a message to indicate that the file is up-to-date, and then stops. If some files have changed, themake command builds only those files that are out-of-date. The command does not rebuild files that are already current.

When the make command runs commands to create a target file, it replaces macros with their values, writes each command line, and then passes the command to a new copy of the shell.