make

Suggestions and warnings

The most common difficulties can arise from your understanding of make's specific meaning of dependency. If file x.c has a:

   #include "defs.h"

line, then the object file x.o depends on defs.h; the source file x.c does not. If defs.h is changed, nothing is done to the file x.c while file x.o must be recreated.

To discover what make would do, the -n option is very useful. The command

   $ make -n

orders make to print out the commands that make would issue without actually taking the time to execute them.

If a change to a file is minor (such as adding a comment to an include file), the -t (touch) option can save a lot of time. Instead of issuing a large number of superfluous recompilations, make updates the modification times on the affected file.

   make -ts

This command (-ts stands for touch silently) causes the relevant files to appear up-to-date. Obvious care is necessary because this mode of operation subverts the intention of make and destroys all memory of the previous relationships.