rcsfile - format of RCS file


An RCS file's contents are described by the grammar below.

The text is free format: space, backspace, tab, newline, vertical tab, form feed, and carriage return (collectively, white space) have no significance except in strings. However, white space cannot appear within an id, num, or sym, and an RCS file must end with a newline.

Strings are enclosed by @. If a string contains a @, it must be doubled; otherwise, strings can contain arbitrary binary data.

The meta syntax uses the following conventions: `|' (bar) separates alternatives; `{' and `}' enclose optional phrases; `{' and `}*' enclose phrases that can be repeated zero or more times; `{' and '}+' enclose phrases that must appear at least once and can be repeated; Terminal symbols are in boldface; nonterminal symbols are in italics.

rcstext ::= admin {delta}* desc {deltatext}* admin ::= head {num}; { branch {num}; } access {id}*; symbols {sym : num}*; locks {id : num}*; {strict ;} { comment {string}; } { expand {string}; } { newphrase }* delta ::= num date num; author id; state {id}; branches {num}*; next {num}; { newphrase }* desc ::= desc string deltatext ::= num log string { newphrase }* text string num ::= {digit | .}+ digit ::= 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 id ::= {num} idchar {idchar | num}* sym ::= {digit}* idchar {idchar | digit}* idchar ::= any visible graphic character except special special ::= $ | , | . | : | ; | @ string ::= @{any character, with @ doubled}*@ newphrase ::= id word* ; word ::= id | num | string | : Identifiers are case sensitive. Keywords are in lower case only. The sets of keywords and identifiers can overlap. In most environments RCS uses the ISO 8859/1 encoding: visible graphic characters are codes 041-176 and 240-377, and white space characters are codes 010-015 and 040.



The delta nodes form a tree. All nodes whose numbers consist of a single pair (e.g., 2.3, 2.1, 1.3, etc.) are on the trunk, and are linked through the next field in order of decreasing numbers. The head field in the admin node points to the head of that sequence (i.e., contains the highest pair). The branch node in the admin node indicates the default branch (or revision) for most RCS operations. If empty, the default branch is the highest branch on the trunk.

All delta nodes whose numbers consist of 2n fields (n2) (e.g.,,, etc.) are linked as follows. All nodes whose first 2n-1 number fields are identical are linked through the next field in order of increasing numbers. For each such sequence, the delta node whose number is identical to the first 2n-2 number fields of the deltas on that sequence is called the branchpoint. The branches field of a node contains 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.

The following diagram shows an example of an RCS file's organization.

Head 2.1 1.3 1.2



Author: Walter F. Tichy, Purdue University, West Lafayette, IN, 47907. Manual Page Revision: 5.6; Release Date: 1995/06/05. Copyright 1982, 1988, 1989 Walter F. Tichy. Copyright 1990, 1991, 1992, 1993, 1994, 1995 Paul Eggert.


rcsintro(1), ci(1), co(1), ident(1), rcs(1), rcsclean(1), rcsdiff(1), rcsmerge(1), rlog(1) Walter F. Tichy, RCS --A System for Version Control, Software--Practice 15, 7 (July 1985), 637-654.
