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HP-UX 11i Version 3: February 2007

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co — check out RCS revisions


co [options] file...


co retrieves revisions from RCS files. Each file name ending in ,v is taken to be an RCS file. All other files are assumed to be working files. co retrieves a revision from each RCS file and stores it in the corresponding working file (see also rcsintro(5)).

Revisions of an RCS file can be checked out locked or unlocked. Locking a revision prevents overlapping updates. A revision checked out for reading or processing (e.g., compiling) need not be locked. A revision checked out for editing and later checked in must normally be locked. Locking a revision currently locked by another user fails (a lock can be broken with the rcs command, but poses inherent risks when independent changes are being made simultaneously (see rcs(1)). co with locking requires the caller to be on the access list of the RCS file unless: he is the owner of the file, a user with appropriate privileges, or the access list is empty. co without locking is not subject to access list restrictions.

A revision is selected by number, check-in date/time, author, or state. If none of these options are specified, the latest revision on the trunk is retrieved. When the options are applied in combination, the latest revision that satisfies all of them is retrieved. The options for date/time, author, and state retrieve a revision on the selected branch. The selected branch is either derived from the revision number (if given), or is the highest branch on the trunk. A revision number can be attached to the options -l, -p, -q, or -r.

The caller of the command must have write permission in the working directory, read permission for the RCS file, and either read permission (for reading) or read/write permission (for locking) in the directory that contains the RCS file.

The working file inherits the read and execute permissions from the RCS file. In addition, the owner write permission is turned on, unless the file is checked out unlocked and locking is set to strict (see rcs(1)).

If a file with the name of the working file exists already and has write permission, co aborts the check out if -q is given, or asks whether to abort if -q is not given. If the existing working file is not writable, it is deleted before the check out.

A number of temporary files are created. A semaphore file is created in the directory of the RCS file to prevent simultaneous update.

A co command applied to an RCS file with no revisions creates a zero-length file. co always performs keyword substitution (see below).



Locks the checked out revision for the caller. If omitted, the checked out revision is not locked. See option -r for handling of the revision number rev.


Prints the retrieved revision on the standard output rather than storing it in the working file. This option is useful when co is part of a pipe.


Quiet mode; diagnostics are not printed.


Retrieves the latest revision on the selected branch whose check in date/time is less than or equal to date. The date and time may be given in free format and are converted to local time. Examples of formats for date:

Tue-PDT, 1981, 4pm Jul 21Free format
Fri April 16 15:52:25 EST 1982Output of ctime(3C)
4/21/86 10:30amFormat: mm/dd/yyhh:mm:ss

Most fields in the date and time can be defaulted. co determines the defaults in the order year, month, day, hour, minute, and second (from most- to least-significant). At least one of these fields must be provided. For omitted fields that are of higher significance than the highest provided field, the current values are assumed. For all other omitted fields, the lowest possible values are assumed. For example, the date 20, 10:30 defaults to 10:30:00 of the 20th of the current month and current year. Date/time fields can be delimited by spaces or commas. If spaces are used, the string must be surrounded by double quotes.

For 2-digit year input (yy) without the presence of the century field, the following interpretation is taken: [70-99, 00-69 (1970-1999, 2000-2069)].


Retrieves the latest revision whose number is less than or equal to rev. If rev indicates a branch rather than a revision, the latest revision on that branch is retrieved. rev is composed of one or more numeric or symbolic fields separated by periods (.). The numeric equivalent of a symbolic field is specified with the ci -n and rcs -n commands (see ci(1) and rcs(1)).


Retrieves the latest revision on the selected branch whose state is set to state.


Retrieves the latest revision on the selected branch that was checked in by the user with login name login. If the argument login is omitted, the caller's login is assumed.


Generates a new revision that is the result of the joining of the revisions on joinlist. joinlist is a comma-separated list of pairs of the form rev2:rev3, where rev2 and rev3 are (symbolic or numeric) revision numbers. For the initial pair, rev1 denotes the revision selected by the options -l, ..., -w. For all other pairs, rev1 denotes the revision generated by the previous pair. (Thus, the output of one join becomes the input to the next.)

For each pair, co joins revisions rev1 and rev3 with respect to rev2. This means that all changes that transform rev2 into rev1 are applied to a copy of rev3. This is particularly useful if rev1 and rev3 are the ends of two branches that have rev2 as a common ancestor. If rev1 < rev2 < rev3 on the same branch, joining generates a new revision that is similar to rev3, but with all changes that lead from rev1 to rev2 undone. If changes from rev2 to rev1 overlap with changes from rev2 to rev3, co prints a warning and includes the overlapping sections, delimited as follows:

<<<<<<< rev1 ======= rev3 >>>>>>>

For the initial pair, rev2 can be omitted. The default is the common ancestor. If any of the arguments indicate branches, the latest revisions on those branches are assumed. If the -l option is present, the initial rev1 is locked.

Keyword Substitution

Strings of the form $keyword$ and $keyword:...$ embedded in the text are replaced with strings of the form $keyword: value $, where keyword and value are pairs listed below. Keywords may be embedded in literal strings or comments to identify a revision.

Initially, the user enters strings of the form $keyword$. On check out, co replaces these strings with strings of the form $keyword: value $. If a revision containing strings of the latter form is checked back in, the value fields are replaced during the next checkout. Thus, the keyword values are automatically updated on checkout.

Keywords and their corresponding values:


The login name of the user who checked in the revision.


The date and time the revision was checked in.


A standard header containing the RCS file name, the revision number, the date, the author, and the state.


The login name of the user who locked the revision (empty if not locked).


The log message supplied during checkin, preceded by a header containing the RCS file name, the revision number, the author, and the date. Existing log messages are not replaced. Instead, the new log message is inserted after $Log:...$. This is useful for accumulating a complete change log in a source file.


The revision number assigned to the revision.


The full pathname of the RCS file.


The state assigned to the revision with rcs -s or ci -s.

Access Control Lists (ACLs)

Optional ACL entries should not be added to RCS files because they might be deleted.


The RCS file name, the working file name, and the revision number retrieved are written to the diagnostic output. The exit status always refers to the last file checked out, and is 0 if the operation was successful, 1 if unsuccessful.


Assume the current directory contains a subdirectory named RCS with an RCS file named io.c,v. Each of the following commands retrieves the latest revision from RCS/io.c,v and stores it into io.c:

co io.c co RCS/io.c,v co io.c,v co io.c RCS/io.c,v co io.c io.c,v co RCS/io.c,v io.c co io.c,v io.c

Check out version 1.1 of RCS file foo.c,v:

co -r1.1 foo.c,v

Check out version 1.1 of RCS file foo.c,v to the standard output:

co -p1.1 foo.c,v

Check out the version of file foo.c,v that existed on September 18, 1992:

co -d"09/18/92" foo.c,v


The co command generates the working file name by removing the ,v from the end of the RCS file name. If the given RCS file name is too long for the file system on which the RCS file should reside, co terminates with an error message.

There is no way to suppress the expansion of keywords, except by writing them differently. In nroff and troff, this is done by embedding the null-character \& into the keyword.

The -d option gets confused in some circumstances, and accepts no date before 1970.

The -j option does not work for files containing lines consisting of a single period (.).

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


co was developed by Walter F. Tichy.

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