MirOS Manual: 14.sccs(PSD)

                             An Introduction to the
                           Source Code Control System

                                  Eric Allman
                                 Project Ingres
                      University of California at Berkeley

               This document gives a quick introduction to  using  the
          Source  Code  Control  System  (SCCS).  The  presentation is
          geared to programmers who are more concerned with what to do
          to get a task done rather than how it works; for this reason
          some of the examples are not well explained. For details  of
          what  the  magic  options  do,  see  the section on "Further

                  This is a working document. Please send  any
                  comments       or       suggestions       to

          1. Introduction

               SCCS is a source management system. Such a system main-
          tains  a  record  of  versions of a system; a record is kept
          with each set of changes of what the changes are,  why  they
          were  made,  and who made them and when. Old versions can be
          recovered, and different versions can be  maintained  simul-
          taneously.  In projects with more than one person, SCCS will
          insure that two people are not editing the same file at  the
          same time.

               All versions of your program, plus the  log  and  other
          information,  is  kept  in a file called the "s-file". There
          are three major operations that can be performed on  the  s-

           (1)   Get a file for compilation (not  for  editing).  This
                 operation  retrieves  a  version of the file from the
                 s-file. By default, the latest version is  retrieved.
                 This  file  is intended for compilation, printing, or
             This is version 1.21 of this document. It was last  modi-
          fied on 12/5/80.

          An Introduction to the Source Code Control System   PS1:14-1

          PS1:14-2   An Introduction to the Source Code Control System

                 whatever; it  is  specifically  NOT  intended  to  be
                 edited  or  changed in any way; any changes made to a
                 file retrieved in this way will probably be lost.

           (2)   Get a file for editing. This operation also retrieves
                 a  version of the file from the s-file, but this file
                 is intended to be edited and then  incorporated  back
                 into  the  s-file.  Only  one person may be editing a
                 file at one time.

           (3)   Merge a file back into the s-file. This is  the  com-
                 panion  operation  to  (2).  A  new version number is
                 assigned, and comments are saved explaining why  this
                 change was made.

          2. Learning the Lingo

               There are a number of terms  that  are  worth  learning
          before we go any farther.

          2.1. S-file

               The s-file is a single file that  holds  all  the  dif-
          ferent  versions  of your file. The s-file is stored in dif-
          ferential format; i.e., only the  differences  between  ver-
          sions  are  stored,  rather  than the entire text of the new
          version. This saves disk space and allows selective  changes
          to  be  removed  later.  Also included in the s-file is some
          header information for each version, including the  comments
          given  by  the person who created the version explaining why
          the changes were made.

          2.2. Deltas

               Each set of changes to the s-file  (which  is  approxi-
          mately  [but  not  exactly!]  equivalent to a version of the
          file) is called a delta. Although technically a  delta  only
          includes  the changes made, in practice it is usual for each
          delta to be made with respect to all the  deltas  that  have
          occurred before[1]. However, it is possible to get a version
          of the file that has selected deltas removed out of the mid-
          dle of the list of changes -- equivalent  to  removing  your
          changes later.

             [1]This matches normal usage, where the previous  changes
          are not saved at all, so all changes are automatically based
          on all other changes that have happened through history.

          An Introduction to the Source Code Control System   PS1:14-3

          2.3. SID's (or, version numbers)

               A SID (SCCS Id) is a number that  represents  a  delta.
          This is normally a two-part number consisting of a "release"
          number and a "level" number.  Normally  the  release  number
          stays  the  same, however, it is possible to move into a new
          release if some major change is being made.

               Since all past deltas are normally applied, the SID  of
          the  final  delta applied can be used to represent a version
          number of the file as a whole.

          2.4. Id keywords

               When you get a version of a file with intent to compile
          and  install  it  (i.e., something other than edit it), some
          special keywords are expanded inline by SCCS. These Id  Key-
          words  can  be used to include the current version number or
          other information into the file. All id keywords are of  the
          form  %x%, where x is an upper case letter. For example, %I%
          is the SID of the latest delta  applied,  %W%  includes  the
          module  name,  SID,  and  a mark that makes it findable by a
          program, and %G% is the date of the  latest  delta  applied.
          There  are many others, most of which are of dubious useful-

               When you get a file for editing, the  id  keywords  are
          not  expanded; this is so that after you put them back in to
          the s-file, they will be expanded automatically on each  new
          version.  But  notice:  if  you  were  to  get them expanded
          accidently, then your file would appear to be the same  ver-
          sion forever more, which would of course defeat the purpose.
          Also, if you should install a version of the program without
          expanding  the  id  keywords,  it will be impossible to tell
          what version it is (since all it will have is "%W%" or what-

          3. Creating SCCS Files

               To put source files into SCCS format, run the following
          shell script from csh:

                  mkdir SCCS save
                  foreach i (*.[ch])
                          sccs admin -i$i $i
                          mv $i save/$i

          This will put the named files into s-files in the  subdirec-
          tory  "SCCS"  The  files  will  be  removed from the current
          directory and hidden away in the directory  "save",  so  the
          next  thing  you  will probably want to do is to get all the
          files (described below). When you are  convinced  that  SCCS

          PS1:14-4   An Introduction to the Source Code Control System

          has  correctly  created  the  s-files, you should remove the
          directory "save".

               If you want to have id keywords in  the  files,  it  is
          best to put them in before you create the s-files. If you do
          not, admin will print "No Id Keywords  (cm7)",  which  is  a
          warning message only.

          4. Getting Files for Compilation

               To get a copy of the latest version of a file, run

                  sccs get prog.c

          SCCS will respond:

                  87 lines

          meaning that version 1.1 was retrieved[2] and that it has 87
          lines. The file prog.c will be created in the current direc-
          tory. The file will be read-only to remind you that you  are
          not supposed to change it.

               This copy of the file should not be changed, since SCCS
          is  unable to merge the changes back into the s-file. If you
          do make changes, they will be lost  the  next  time  someone
          does a get.

          5. Changing Files (or, Creating Deltas)

          5.1. Getting a copy to edit

               To edit a source file, you must first get it,  request-
          ing permission to edit it[3]:

                  sccs edit prog.c

          The response will be the same as with  get  except  that  it
          will also say:

                  New delta 1.2

             [2]Actually, the SID of the final delta applied was 1.1.
             [3]The  "edit" command is equivalent to using the -e flag
          to get, as:

                  sccs get -e prog.c

          Keep this in mind when reading other documentation.

          An Introduction to the Source Code Control System   PS1:14-5

          You then edit it, using a standard text editor:

                  vi prog.c

          5.2. Merging the changes back into the s-file

               When the desired changes are made,  you  can  put  your
          changes into the SCCS file using the delta command:

                  sccs delta prog.c

               Delta will prompt you for "comments?" before it  merges
          the  changes  in.  At this prompt you should type a one-line
          description of what the changes  mean  (more  lines  can  be
          entered   by  ending  each  line  except  the  last  with  a
          backslash[4]). Delta will then type:

                  5 inserted
                  3 deleted
                  84 unchanged

          saying that delta 1.2 was  created,  and  it  inserted  five
          lines, removed three lines, and left 84 lines  unchanged[5].
          The  prog.c  file will be removed; it can be retrieved using

          5.3. When to make deltas

               It is probably unwise to  make  a  delta  before  every
          recompilation  or  test; otherwise, you tend to get a lot of
          deltas with comments like "fixed compilation problem in pre-
          vious  delta"  or  "fixed botch in 1.3". However, it is very
          important to delta everything before installing a module for
          general use. A good technique is to edit the files you need,
          make all necessary changes and tests, compiling and  editing
          as  often  as  necessary without making deltas. When you are
          satisfied that you have a working version, delta  everything
          being edited, re-get them, and recompile everything.

          5.4. What's going on: the info command

               To find out what files where being edited, you can use:

                  sccs info
             [4]Yes, this is a stupid default.
             [5]Changes  to a line are counted as a line deleted and a
          line inserted.

          PS1:14-6   An Introduction to the Source Code Control System

          to print out all the files being edited and  other  informa-
          tion  such  as  the name of the user who did the edit. Also,
          the command:

                  sccs check

          is nearly equivalent to the info command, except that it  is
          silent if nothing is being edited, and returns non-zero exit
          status if anything is being edited; it can  be  used  in  an
          "install"  entry  in a makefile to abort the install if any-
          thing has not been properly deltaed.

               If you know that everything being edited should be del-
          taed, you can use:

                  sccs delta `sccs tell`

          The tell command is similar to info  except  that  only  the
          names of files being edited are output, one per line.

               All  of  these  commands  take  a  -b  flag  to  ignore
          "branches"  (alternate versions, described later) and the -u
          flag to only give files being edited by  you.  The  -u  flag
          takes  an  optional  user  argument, giving only files being
          edited by that user. For example,

                  sccs info -ujohn

          gives a listing of files being edited by john.

          5.5. ID keywords

               Id keywords can be inserted into your file that will be
          expanded automatically by get. For example, a line such as:

                  static char SccsId[] = "%W%\t%G%";

          will be replaced with something like:

                  static char SccsId[] = "@(#)prog.c      1.2     08/29/80";

          This tells you the name and version of the source  file  and
          the  time the delta was created. The string "@(#)" is a spe-
          cial string which signals the beginning of an SCCS  Id  key-

          5.5.1. The what command

               To find out what version of a  program  is  being  run,

                  sccs what prog.c /usr/bin/prog

          An Introduction to the Source Code Control System   PS1:14-7

          which will print  all  strings  it  finds  that  begin  with
          "@(#)". This works on all types of files, including binaries
          and libraries. For example, the above  command  will  output
          something like:

                          prog.c  1.2     08/29/80
                          prog.c  1.1     02/05/79

          From this I can see that the source that I  have  in  prog.c
          will  not  compile  into  the  same version as the binary in

          5.5.2. Where to put id keywords

               ID keywords can be inserted anywhere, including in com-
          ments,  but  Id  Keywords  that are compiled into the object
          module are especially useful, since it  lets  you  find  out
          what  version  of  the  object  is being run, as well as the
          source. However, there is a cost: data space is used  up  to
          store the keywords, and on small address space machines this
          may be prohibitive.

               When you put id  keywords  into  header  files,  it  is
          important  that  you assign them to different variables. For
          example, you might use:

                  static char AccessSid[] = "%W%  %G%";

          in the file access.h and:

                  static char OpsysSid[] = "%W%   %G%";

          in the file opsys.h. Otherwise,  you  will  get  compilation
          errors  because "SccsId" is redefined. The problem with this
          is that if the header file is included by many modules  that
          are  loaded together, the version number of that header file
          is included in the object module many times; you may find it
          more  to  your  taste  to put id keywords in header files in

          5.6. Keeping SID's consistent across files

               With some care, it is possible to keep the  SID's  con-
          sistent  in  multi-file systems. The trick here is to always
          edit all files at once. The changes  can  then  be  made  to
          whatever  files are necessary and then all files (even those
          not changed) are redeltaed. This can be done  fairly  easily
          by  just  specifying the name of the directory that the SCCS
          files are in:

                  sccs edit SCCS

          PS1:14-8   An Introduction to the Source Code Control System

          which will edit all files in that  directory.  To  make  the
          delta, use:

                  sccs delta SCCS

          You will be prompted for comments only once.

          5.7. Creating new releases

               When you want to create a new release of a program, you
          can  specify  the  release  number you want to create on the
          edit command. For example:

                  sccs edit -r2 prog.c

          will cause the next delta to be in release two (that is,  it
          will  be  numbered 2.1). Future deltas will automatically be
          in release two. To change the release number  of  an  entire
          system, use:

                  sccs edit -r2 SCCS

          6. Restoring Old Versions

          6.1. Reverting to old versions

               Suppose that after delta 1.2 was stable  you  made  and
          released a delta 1.3. But this introduced a bug, so you made
          a delta 1.4 to correct it. But 1.4 was still buggy, and  you
          decided  you wanted to go back to the old version. You could
          revert to delta 1.2 by choosing the SID in a get:

                  sccs get -r1.2 prog.c

          This will produce a version of prog.c that is delta 1.2 that
          can be reinstalled so that work can proceed.

               In some cases you don't know what the SID of the  delta
          you  want  is. However, you can revert to the version of the
          program that was running as of a certain date by  using  the
          -c (cutoff) flag. For example,

                  sccs get -c800722120000 prog.c

          will retrieve whatever version was current as  of  July  22,
          1980  at 12:00 noon. Trailing components can be stripped off
          (defaulting to their highest legal value),  and  punctuation
          can  be  inserted  in  the  obvious places; for example, the
          above line could be equivalently stated:

                  sccs get -c"80/07/22 12:00:00" prog.c

          An Introduction to the Source Code Control System   PS1:14-9

          6.2. Selectively deleting old deltas

               Suppose that you  later  decided  that  you  liked  the
          changes  in delta 1.4, but that delta 1.3 should be removed.
          You could do this by excluding delta 1.3:

                  sccs edit -x1.3 prog.c

          When delta 1.5 is made, it will include the changes made  in
          delta  1.4,  but will exclude the changes made in delta 1.3.
          You can exclude a range of deltas using a dash. For example,
          if you want to get rid of 1.3 and 1.4 you can use:

                  sccs edit -x1.3-1.4 prog.c

          which will exclude all deltas  from  1.3  to  1.4.  Alterna-

                  sccs edit -x1.3-1 prog.c

          will exclude a range of  deltas  from  1.3  to  the  current
          highest delta in release 1.

               In certain cases when using -x (or -i; see below) there
          will  be  conflicts between versions; for example, it may be
          necessary to both include and delete a particular  line.  If
          this  happens,  SCCS always prints out a message telling the
          range of lines effected; these lines should then be examined
          very carefully to see if the version SCCS got is ok.

               Since each delta (in the sense of "a set  of  changes")
          can  be  excluded at will, that this makes it most useful to
          put each semantically distinct change into its own delta.

          7. Auditing Changes

          7.1. The prt command

               When you created a delta, you presumably gave a  reason
          for  the delta to the "comments?" prompt. To print out these
          comments later, use:

                  sccs prt prog.c

          This will produce a report for each delta of the  SID,  time
          and  date of creation, user who created the delta, number of
          lines inserted, deleted, and  unchanged,  and  the  comments
          associated  with  the  delta. For example, the output of the
          above command might be:

          PS1:14-10  An Introduction to the Source Code Control System

                  D 1.2   80/08/29 12:35:31       bill    2       1       00005/00003/00084
                  removed "-q" option

                  D 1.1   79/02/05 00:19:31       eric    1       0       00087/00000/00000
                  date and time created 80/06/10 00:19:31 by eric

          7.2. Finding why lines were inserted

               To find out why you inserted lines, you can get a  copy
          of  the file with each line preceded by the SID that created

                  sccs get -m prog.c

          You can then find out what this delta did  by  printing  the
          comments using prt.

               To find out what lines are associated with a particular
          delta (e.g., 1.3), use:

                  sccs get -m -p prog.c | grep '^1.3'

          The -p flag causes SCCS to output the  generated  source  to
          the standard output rather than to a file.

          7.3. Finding what changes you have made

               When you are editing a file,  you  can  find  out  what
          changes you have made using:

                  sccs diffs prog.c

          Most of the ``diff'' flags can be used. To pass the -c flag,
          use -C.

               To compare two versions that are in deltas, use:

                  sccs sccsdiff -r1.3 -r1.6 prog.c

          to see the differences between delta 1.3 and delta 1.6.

          8. Shorthand Notations

               There are several sequences of commands that  get  exe-
          cuted frequently. Sccs tries to make it easy to do these.

          8.1. Delget

               A frequent requirement is to make a delta of some  file
          and then get that file. This can be done by using:

                  sccs delget prog.c

          An Introduction to the Source Code Control System  PS1:14-11

          which is entirely equivalent to using:

                  sccs delta prog.c
                  sccs get prog.c

          The "deledit" command is equivalent to "delget" except  that
          the "edit" command is used instead of the "get" command.

          8.2. Fix

               Frequently, there are small bugs in deltas, e.g.,  com-
          pilation errors, for which there is no reason to maintain an
          audit trail. To replace a delta, use:

                  sccs fix -r1.4 prog.c

          This will get a copy of delta 1.4 of prog.c for you to  edit
          and  then delete delta 1.4 from the SCCS file. When you do a
          delta of prog.c, it will be delta 1.4  again.  The  -r  flag
          must be specified, and the delta that is specified must be a
          leaf delta, i.e., no other deltas may have been made  subse-
          quent to the creation of that delta.

          8.3. Unedit

               If you found you edited a file that you did not want to
          edit, you can back out by using:

                  sccs unedit prog.c

          8.4. The -d flag

               If you are working on a project where the SCCS code  is
          in a directory somewhere, you may be able to simplify things
          by using a shell alias. For example, the alias:

                  alias syssccs sccs -d/usr/src

          will allow you to issue commands such as:

                  syssccs edit cmd/who.c

          which will look for the file "/usr/src/cmd/SCCS/who.c".  The
          file  "who.c"  will always be created in your current direc-
          tory regardless of the value of the -d flag.

          9. Using SCCS on a Project

               Working on a project with several people  has  its  own
          set  of  special  problems. The main problem occurs when two
          people modify a file at the same time. SCCS prevents this by
          locking an s-file while it is being edited.

          PS1:14-12  An Introduction to the Source Code Control System

               As a result, files should not be reserved  for  editing
          unless  they  are  actually  being edited at the time, since
          this will prevent other people on the  project  from  making
          necessary  changes. For example, a good scenario for working
          might be:

                  sccs edit a.c g.c t.c
                  vi a.c g.c t.c
                  # do testing of the (experimental) version
                  sccs delget a.c g.c t.c
                  sccs info
                  # should respond "Nothing being edited"
                  make install

               As a general rule, all source files should  be  deltaed
          before  installing  the  program  for general use. This will
          insure that it is possible to restore any version in use  at
          any time.

          10. Saving Yourself

          10.1. Recovering a munged edit file

               Sometimes you may  find  that  you  have  destroyed  or
          trashed a file that  you  were  trying  to  edit[6].  Unfor-
          tunately,  you  can't  just  remove  it and re-edit it; SCCS
          keeps track of the fact that someone is trying to  edit  it,
          so it won't let you do it again. Neither can you just get it
          using get, since that would expand the Id keywords. Instead,
          you can say:

                  sccs get -k prog.c

          This will not expand the Id keywords, so it is safe to do  a
          delta with it.

               Alternately, you can unedit and edit the file.

          10.2. Restoring the s-file

               In particularly bad circumstances, the SCCS file itself
          may  get munged. The most common way this happens is that it
          gets edited. Since SCCS  keeps  a  checksum,  you  will  get
          errors  every  time you read the file. To fix this checksum,

                  sccs admin -z prog.c

             [6]Or given up and decided to start over.

          An Introduction to the Source Code Control System  PS1:14-13

          11. Using the Admin Command

               There are a number of parameters that can be set  using
          the  admin command. The most interesting of these are flags.
          Flags can be added by using the -f flag. For example:

                  sccs admin -fd1 prog.c

          sets the "d" flag to the value "1". This flag can be deleted
          by using:

                  sccs admin -dd prog.c

          The most useful flags are:

          b      Allow branches to be made using the -b flag to edit.

          dSID   Default SID to be used on a get or edit. If  this  is
                 just  a release number it constrains the version to a
                 particular release only.

          i      Give a fatal error if there are no Id Keywords  in  a
                 file.  This  is useful to guarantee that a version of
                 the file does not get merged into the s-file that has
                 the  Id  Keywords  inserted  as  constants instead of
                 internal forms.

          y      The "type" of the module. Actually, the value of this
                 flag  is  unused  by SCCS except that it replaces the
                 %Y% keyword.

               The -tfile flag can be used to store  descriptive  text
          from  file. This descriptive text might be the documentation
          or a design and implementation document. Using the  -t  flag
          insures  that  if  the  SCCS file is sent, the documentation
          will be sent also. If file is omitted, the descriptive  text
          is deleted. To see the descriptive text, use "prt -t".

               The admin command can be  used  safely  any  number  of
          times on files. A file need not be gotten for admin to work.

          12. Maintaining Different Versions (Branches)

               Sometimes it is convenient to maintain an  experimental
          version  of  a  program  for an extended period while normal
          maintenance continues on the version in production. This can
          be  done  using  a  "branch."  Normally deltas continue in a
          straight line, each depending on the delta before.  Creating
          a branch "forks off" a version of the program.

               The ability to  create  branches  must  be  enabled  in
          advance using:

          PS1:14-14  An Introduction to the Source Code Control System

                  sccs admin -fb prog.c

          The -fb flag can be specified when the SCCS  file  is  first

          12.1. Creating a branch

               To create a branch, use:

                  sccs edit -b prog.c

          This will create a branch with (for  example)  SID
          The deltas for this version will be numbered 1.5.1.n.

          12.2. Getting from a branch

               Deltas in a branch are normally not included  when  you
          do a get. To get these versions, you will have to say:

                  sccs get -r1.5.1 prog.c

          12.3. Merging a branch back into the main trunk

               At some point you will have  finished  the  experiment,
          and  if  it  was  successful you will want to incorporate it
          into the release version. But in the  meantime  someone  may
          have  created  a  delta 1.6 that you don't want to lose. The

                  sccs edit -i1.5.1.1-1.5.1 prog.c
                  sccs delta prog.c

          will merge all of your changes into the release  system.  If
          some  of  the changes conflict, get will print an error; the
          generated result should be  carefully  examined  before  the
          delta is made.

          12.4. A more detailed example

               The following technique might be  used  to  maintain  a
          different version of a program. First, create a directory to
          contain the new version:

                  mkdir ../newxyz
                  cd ../newxyz

          Edit a copy of the program on a branch:

                  sccs -d../xyz edit prog.c

          When using the old version, be sure to use the  -b  flag  to
          info,  check,  tell,  and  clean  to  avoid  confusion.  For

          An Introduction to the Source Code Control System  PS1:14-15

          example, use:

                  sccs info -b

          when in the directory "xyz".

               If you want to save a copy of the program (still on the
          branch) back in the s-file, you can use:

                  sccs -d../xyz deledit prog.c

          which will do a delta on the branch and reedit it for you.

               When the experiment is complete, merge it back into the
          s-file using delta:

                  sccs -d../xyz delta prog.c

          At this point you must decide whether this version should be
          merged back into the trunk (i.e. the default version), which
          may have undergone changes. If so, it can  be  merged  using
          the -i flag to edit as described above.

          12.5. A warning

               Branches should be kept to a minimum. After  the  first
          branch  from  the  trunk,  SID's  are assigned rather hapha-
          zardly, and the structure gets complex fast.

          13. Using SCCS with Make

               SCCS and make can be made to work together with a  lit-
          tle care. A few sample makefiles for common applications are

               There are a few basic entries that every makefile ought
          to have. These are:

          a.out     (or whatever the makefile generates.)  This  entry
                    regenerates  whatever this makefile is supposed to
                    regenerate.  If  the  makefile  regenerates   many
                    things,  this should be called "all" and should in
                    turn have dependencies on everything the  makefile
                    can generate.

          install   Moves the objects  to  the  final  resting  place,
                    doing any special chmod's or ranlib's as appropri-

          sources   Creates all the source files from SCCS files.

          clean     Removes all files from the current directory  that
                    can be regenerated from SCCS files.

          PS1:14-16  An Introduction to the Source Code Control System

          print     Prints the contents of the directory.

          The examples shown below are only partial examples, and  may
          omit  some of these entries when they are deemed to be obvi-

               The clean entry should not remove  files  that  can  be
          regenerated  from  the SCCS files. It is sufficiently impor-
          tant to have the source files around at all times  that  the
          only  time  they  should be removed is when the directory is
          being mothballed. To do this, the command:

                  sccs clean

          can be used. This will remove all files for which an  s-file
          exists, but which is not being edited.

          13.1. To maintain single programs

               Frequently there are directories with  several  largely
          unrelated  programs  (such as simple commands). These can be
          put into a single makefile:

                  LDFLAGS= -i -s

                  prog: prog.o
                          $(CC) $(LDFLAGS) -o prog prog.o
                  prog.o: prog.c prog.h

                  example: example.o
                          $(CC) $(LDFLAGS) -o example example.o
                  example.o: example.c

                          sccs get $<

          The trick here is that the .DEFAULT  rule  is  called  every
          time  something  is needed that does not exist, and no other
          rule exists to make it. The explicit dependency  of  the  .o
          file  on  the .c file is important. Another way of doing the
          same thing is:

          An Introduction to the Source Code Control System  PS1:14-17

                  SRCS=   prog.c prog.h example.c

                  LDFLAGS= -i -s

                  prog: prog.o
                          $(CC) $(LDFLAGS) -o prog prog.o
                  prog.o: prog.h

                  example: example.o
                          $(CC) $(LDFLAGS) -o example example.o

                  sources: $(SRCS)
                          sccs get $@

          There are a couple of advantages to this approach:  (1)  the
          explicit  dependencies  of  the  .o  on the .c files are not
          needed, (2) there is an entry called  "sources"  so  if  you
          want to get all the sources you can just say "make sources",
          and (3) the makefile is less likely to do  confusing  things
          since it won't try to get things that do not exist.

          13.2. To maintain a library

               Libraries that are  largely  static  are  best  updated
          using  explicit  commands,  since  make  doesn't  know about
          updating them properly. However, libraries that are  in  the
          process  of being developed can be handled quite adequately.
          The problem is that the .o files have to be kept out of  the
          library as well as in the library.

          PS1:14-18  An Introduction to the Source Code Control System

                  # configuration information
                  OBJS=   a.o b.o c.o d.o
                  SRCS=   a.c b.c c.c d.s x.h y.h z.h
                  TARG=   /usr/lib

                  # programs
                  GET=    sccs get
                  AR=     -ar
                  RANLIB= ranlib

                  lib.a: $(OBJS)
                          $(AR) rvu lib.a $(OBJS)
                          $(RANLIB) lib.a

                  install: lib.a
                          sccs check
                          cp lib.a $(TARG)/lib.a
                          $(RANLIB) $(TARG)/lib.a

                  sources: $(SRCS)
                          $(GET) $(REL) $@

                  print: sources
                          pr *.h *.[cs]
                          rm -f *.o
                          rm -f core a.out $(LIB)

               The "$(REL)" in the get can be used to get old versions
          easily; for example:

                  make b.o REL=-r1.3

               The install entry includes the line "sccs check" before
          anything  else.  This guarantees that all the s-files are up
          to date (i.e., nothing is being edited), and will abort  the
          make if this condition is not met.

          13.3. To maintain a large program

          An Introduction to the Source Code Control System  PS1:14-19

                  OBJS=   a.o b.o c.o d.o
                  SRCS=   a.c b.c c.y d.s x.h y.h z.h

                  GET=    sccs get

                  a.out: $(OBJS)
                          $(CC) $(LDFLAGS) $(OBJS) $(LIBS)

                  sources: $(SRCS)
                          $(GET) $(REL) $@

          (The print and clean entries are identical to  the  previous
          case.)  This  makefile  requires  copies  of  the source and
          object files to be kept during development. It  is  probably
          also wise to include lines of the form:

                  a.o: x.h y.h
                  b.o: z.h
                  c.o: x.h y.h z.h
                  z.h: x.h

          so that modules will be recompiled if header files change.

               Since make does not do transitive closure on  dependen-
          cies, you may find in some makefiles lines like:

                  z.h: x.h
                          touch z.h

          This would be used in cases where file z.h has a line:

                  #include "x.h"

          in order to bring the mod date of z.h in line with  the  mod
          date  of  x.h.  When  you have a makefile such as above, the
          touch command can  be  removed  completely;  the  equivalent
          effect will be achieved by doing an automatic get on z.h.

          14. Further Information

               The SCCS/PWB User's Manual gives a  deeper  description
          of how to use SCCS. Of particular interest are the numbering
          of branches, the l-file, which gives a description  of  what
          deltas were used on a get, and certain other SCCS commands.

               The SCCS manual pages are a  good  last  resort.  These
          should  be  read by software managers and by people who want
          to know everything about everything.

               Both of these documents were written without  the  sccs
          front  end  in  mind,  so  most of the examples are slightly

          PS1:14-20  An Introduction to the Source Code Control System

          different from those in this document.

          An Introduction to the Source Code Control System  PS1:14-21

                                Quick Reference

          1. Commands

               The following commands  should  all  be  preceded  with
          "sccs".  This  list  is not exhaustive; for more options see
          Further Information.

          get      Gets files for compilation (not  for  editing).  Id
                   keywords are expanded.

                   -rSID   Version to get.

                   -p      Send to standard output rather than to  the
                           actual file.

                   -k      Don't expand id keywords.

                   -ilist  List of deltas to include.

                   -xlist  List of deltas to exclude.

                   -m      Precede each  line  with  SID  of  creating

                   -cdate  Don't apply any deltas created after date.

          edit     Gets  files  for  editing.  Id  keywords  are   not
                   expanded. Should be matched with a delta command.

                   -rSID   Same as get. If  SID  specifies  a  release
                           that  does  not yet exist, the highest num-
                           bered delta is retrieved and the new  delta
                           is numbered with SID.

                   -b      Create a branch.

                   -ilist  Same as get.

                   -xlist  Same as get.

          delta    Merge a file gotten using edit  back  into  the  s-
                   file.  Collect  comments  about  why this delta was

          unedit   Remove a  file  that  has  been  edited  previously
                   without merging the changes into the s-file.

          prt      Produce a report of changes.

          PS1:14-22  An Introduction to the Source Code Control System

                   -t   Print the descriptive text.

                   -e   Print (nearly) everything.

          info     Give a list of all files being edited.

                   -b   Ignore branches.

                        Ignore files not being edited by user.

          check    Same as info, except that  nothing  is  printed  if
                   nothing   is   being  edited  and  exit  status  is

          tell     Same as info, except that one line is produced  per
                   file being edited containing only the file name.

          clean    Remove all files that can be regenerated  from  the

          what     Find and print id keywords.

          admin    Create or set parameters on s-files.

                   -ifile  Create, using file as the initial contents.

                   -z      Rebuild the checksum in case the  file  has
                           been trashed.

                   -fflag  Turn on the flag.

                   -dflag  Turn off (delete) the flag.

                   -tfile  Replace the descriptive text in the  s-file
                           with the contents of file. If file is omit-
                           ted, the text is deleted. Useful for  stor-
                           ing  documentation or "design & implementa-
                           tion" documents to insure they get  distri-
                           buted with the s-file.

                   Useful flags are:

                   b       Allow branches to be made using the -b flag
                           to edit.

                   dSID    Default SID to be used on a get or edit.

                   i       Cause "No Id Keywords" error message to  be
                           a fatal error rather than a warning.

                   t       The module "type"; the value of  this  flag
                           replaces the %Y% keyword.

          An Introduction to the Source Code Control System  PS1:14-23

          fix      Remove a delta and reedit it.

          delget   Do a delta followed by a get.

          deledit  Do a delta followed by an edit.

          2. Id Keywords

          %Z%   Expands to "@(#)" for the what command to find.

          %M%   The current module name, e.g., "prog.c".

          %I%   The highest SID applied.

          %W%   A shorthand for "%Z%%M% <tab> %I%".

          %G%   The date of the delta corresponding to the "%I%"  key-

          %R%   The current release number, i.e., the first  component
                of the "%I%" keyword.

          %Y%   Replaced by the value of the t flag (set by admin).

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