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.
Dates, which appear after the date keyword, are of the form Y.mm.dd.hh.mm.ss, where Y is the year, mm the month (01-12), dd the day (01-31), hh the hour (00-23), mm the minute (00-59), and ss the second (00-60). Y contains just the last two digits of the year for years from 1900 through 1999, and all the digits of years thereafter. Dates use the Gregorian calendar; times use UTC.
The newphrase productions in the grammar are reserved for future extensions to the format of RCS files. No newphrase will begin with any keyword already in use.
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 (n>=2) (e.g., 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 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
|
|
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 /
\ /
\ /
\ /