(make.info.gz) Rule Syntax

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 4.2 Rule Syntax
 ===============
 
 In general, a rule looks like this:
 
      TARGETS : PREREQUISITES
              RECIPE
              ...
 
 or like this:
 
      TARGETS : PREREQUISITES ; RECIPE
              RECIPE
              ...
 
    The TARGETS are file names, separated by spaces.  Wildcard
 characters may be used ( Using Wildcard Characters in File Names
 Wildcards.) and a name of the form `A(M)' represents member M in
 archive file A ( Archive Members as Targets Archive Members.).
 Usually there is only one target per rule, but occasionally there is a
 reason to have more ( Multiple Targets in a Rule Multiple
 Targets.).
 
    The RECIPE lines start with a tab character (or the first character
 in the value of the `.RECIPEPREFIX' variable;  Special
 Variables).  The first recipe line may appear on the line after the
 prerequisites, with a tab character, or may appear on the same line,
 with a semicolon.  Either way, the effect is the same.  There are other
 differences in the syntax of recipes.   Writing Recipes in Rules
 Recipes.
 
    Because dollar signs are used to start `make' variable references,
 if you really want a dollar sign in a target or prerequisite you must
 write two of them, `$$' ( How to Use Variables Using Variables.).
 If you have enabled secondary expansion ( Secondary Expansion)
 and you want a literal dollar sign in the prerequisites list, you must
 actually write _four_ dollar signs (`$$$$').
 
    You may split a long line by inserting a backslash followed by a
 newline, but this is not required, as `make' places no limit on the
 length of a line in a makefile.
 
    A rule tells `make' two things: when the targets are out of date,
 and how to update them when necessary.
 
    The criterion for being out of date is specified in terms of the
 PREREQUISITES, which consist of file names separated by spaces.
 (Wildcards and archive members ( Archives) are allowed here too.)
 A target is out of date if it does not exist or if it is older than any
 of the prerequisites (by comparison of last-modification times).  The
 idea is that the contents of the target file are computed based on
 information in the prerequisites, so if any of the prerequisites
 changes, the contents of the existing target file are no longer
 necessarily valid.
 
    How to update is specified by a RECIPE.  This is one or more lines
 to be executed by the shell (normally `sh'), but with some extra
 features ( Writing Recipes in Rules Recipes.).
 

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