DIF-SSED.DOC Reducing the Swelling of the Phone Bill with DIF and SSED November 17, 1981 Chuck Forsberg Computer Development Inc Beaverton OR Lately (if not sooner) it has become obvious that there must be a better and cheaper way to distribute software updates to changing programs than to transmit all of the new files in their totality, even though only a few lines in each have been changed. For some years the Unix differential file print program diff(1) (the (1) refers to the section of the Unix Programmers Manual in which it is described) has had a -e flag which provides a set of ed commands suitable for transforming the first file to the second. With these tools, only an update file need be transmitted, provided, of course, that both the sender and the receiver had copies of the same antecdent file. I have written a "new" diff called dif.c which manages to operate in the primitive CP/M environment. The editing commands output in response to the -e option refrence sequential lines in the source files, so they (the commands) can be executed by a stream editor. (The Unix diff(1) creates difference files with non-forward-sequential commands.) To generate a difference file, the command is dif -e oldfile newfile >file.dif The >file.dif redirects the standard output to the file. A + may be susbtituted for > if simultaneous console output is desired. The receiver then invokes: ssed oldfile newfile Which will result in newfile being created identical to the oroginal newfile. Well, not precisely identical, but identical up to and including the EOF (^Z) character. The dribble after that may change, so CRCK may say they are different. To check, compare the two files with dif. Unix folks with 14 character file names and modification times stored by the filesystem have little trouble keeping the files synchronized. (If the antecedent files are different, there's no telling what the output file will look like!) For us poor CP/M folks (verrry) patiently awaiting something like Unix to appear magically on out desktops, I propose that the revision or revision date of the antecedent file be placed in the new file adjacent to the new revision or date, preferably on the same line. This way the user may easily verify that he has the correct antecedent. Dif Versions 1.10 and later place hash indices of the RETAINED lines of the antecedent file in the difference output. This allows ssed 1.10 or later to verify correctness of the antecedent file. the new .dif files are compatible with the old ssed, but, alas, not with Unix ed or sed. The array sizes in dif.c may have to be shrunk somewhat to run on a 48k system. For testing, give dif -e filea fileb |ssed filea >filec dif fileb filec (fileb and filec should be identical) It ought to work if you said dif -e filea fileb |ssed filea |dif fileb and it does, with version 2.0. Version 2.0 of dif.c adds a -u flag which will unsqueeze filea before comparing it to fileb. Thus you can say sq filea dif -eu filea.qqq fileb |ssed filea |dif fileb Or you can say dif -eu filea.qqq fileb |ssed -u filea.qqq |dif fileb to test dif and ssed. (Be sure dif and ssed are exactly where you say they are, or else pipes will be broken.) Restriction: Since the BDS Standard I/O library and the Directed I/O package are somewhat confused about translation between CP/M's cr/lf terminated lines and **nixs' \n terminated lines, dif was written to strip cr's from the input in order that only one cr appear on the output. As a result, lines terminated by cr/lf, lf, and lf/cr all come out the same! This would munge files where lf/cr has a special meaning (MBASIC continuation lines) or where embedded cr's are used (RTTY art). Unix is a trademark of WECO, CP/M of Digital Research.