rcsfile(4)						     Kernel Interfaces Manual							rcsfile(4)

NAME

       rcsfile - format of RCS files

DESCRIPTION

       An RCS file is an ASCII file.  Its contents are described by the grammar below.	The text is free format, that is, spaces, tabs and newline
       characters have no significance except in strings.  Strings are enclosed by symbols.  If a string contains the symbol, the symbol  must	be
       doubled.

       The meta syntax uses the following conventions:

		|      (bar)		  Separates alternatives.
	      {...}    (braces) 	  Enclose optional phrases.
	      {...}*   (braces star)	  Enclose  phrases  that  may  be repeated
					  zero or more times.
	      {...}+   (braces plus)	  Enclose  phrases  that  must	appear	at
					  least once and may be repeated.
	      <...>    (angle brackets)   Enclose nonterminals.

   RCS File Grammar
       Identifiers are case sensitive.	Keywords are in lowercase only.  The sets of keywords and identifiers may overlap.

       <rcstext>   ::= <admin> {<delta>}* <desc> {<deltatext>}*

       <admin>	   ::= head    {<num>};
		       access  {<id>}*;
		       symbols {<id> : <num>}*;
		       locks   {<id> : <num>}*; {strict ;}
		       comment {<string>};

       <delta>	   ::= <num>
		       date    <num>;
		       author  <id>;
		       state   {<id>};
		       branches {<num>}*;
		       next    {<num>};

       <desc>	   ::= desc    <string>

       <deltatext> ::= <num>
		       log     <string>
		       text    <string>

       <num>	   ::= {<digit>{.}}+

       <digit>	   ::= 0 | 1 | ... | 9

       <id>	   ::= <letter>{<idchar>}*

       <letter>    ::= A | B | ... | Z | a | b | ... | z

       <idchar>    ::= Any printing ASCII character except space,
		       tab, carriage return, newline, and <special>.

       <special>   ::= ; | : | , | @

       <string>    ::= @{any ASCII character, with "@" doubled}*@

   RCS File Structure
       The  nodes  form  a  tree.   All nodes whose numbers consist of a single pair (for example, 2.3, 2.1, 1.3, etc.)  are on the trunk, and are
       linked through the field in order of decreasing numbers.  The field in the node points to the head of that sequence (that is, contains  the
       highest pair).

       All  nodes  whose  numbers consist of 2n fields (n>=2) (for example, 3.1.1.1, 2.1.2.2, etc.)  are linked as follows.  All nodes whose first
       (2n)-1 number fields are identical are linked through the field in order of increasing numbers.	For each such  sequence,  the  node  whose
       number  is  identical to the first 2(n-1) number fields of the deltas on that sequence is called the branchpoint.  The field of a node con-
       tains a list of the numbers of the first nodes of all sequences for which it is a branchpoint.  This list is ordered in increasing numbers.

EXAMPLES

				    head
				      |
				      |
				      v
				  ---------
	    /  	 / 	  |	  |	 / 	       / 
	   /   	/   	  |  2.1  |	/   	      /   
	  /	      /     	  |	  |    /     	   __/	   \__
	 /1.2.1.3    /1.3.1.1   |	  |   /1.2.2.2   /1.2.2.1.1.1
	 ---------    ---------   ---------   ---------   -------------
	     ^		  ^	      | 	  ^		^
	     |		  |	      | 	  |		|
	     |		  |	      v 	  |		|
	    /  	  |	  ---------	 / 		|
	   /   	  |	    1.3  /	/   		|
	  /		  ---------	 /     /     -----------
	 /1.2.1.1		    	/     /1.2.2.1
	 ---------		      /      ---------
	     ^			      | 	  ^
	     |			      | 	  |
	     |			      v 	  |
	     |			  ---------	  |
	     |			    1.2  /	  |
	     ----------------------	 /---------
				    	/
				      /
				      |
				      |
				      v
				  ---------
				    1.1  /
				   	 /
				    	/
				      /

WARNINGS

       RCS is designed to be used with text (ASCII) files only.  Using RCS with nontext (binary) files results in data corruption.

AUTHOR

       was developed by Walter F. Tichy, Purdue University, West Lafayette, IN 47907, USA.

       1982 by Walter F. Tichy.

SEE ALSO

       ci(1), co(1), ident(1), rcs(1), rcsdiff(1), rcsmerge(1), rlog(1), rcsintro(5).

																	rcsfile(4)