c Xerox Corporation 1979Inter-Office MemorandumToAlto UsersDateJuly 9, 1982FromMartin Newell, Beau Sheil,SubjectIF - Conditional execution ofPeter Deutsch, Dan SwinehartcommandsFiled on[Maxc/Indigo]If.pressXEROX INTRODUCTIONThe program If implements conditional execution of groups of commands to the AltoExecutive. The conditions involve the existence, lengths, and read/write dates of files, aswell as string matching on the contents of files. The original motivation for If was its usein conjunction with the Bravo macros for compiling BCPL and MESA programs, though otheruses have become apparent.ExampleThe Mesa compiler creates an .errlog file only if there were errors. Thus, a command filefor compiling a Mesa program, prog.mesa, then entering Bravo only if there were errors is:Delete prog.errlogCompiler -p/c prog.mesaIf prog.errlog then Bravo/m progThis is a modification of the m quit macro in bravo for MESA. Also see Examples at theend of this document.Where to find IfIf is on: [Maxc]If.runSPECIFICATIONSyntaxIf [ then ][ else ]where [] denotes an optional clause, and is one of:filename(yields true if file exists)filename/l=N(yields true if file exists and length = N)filename/lN(yields true if file exists and length > N)filename/s(yields true if file exists and contains )filename/r=otherfilename/r(yields true if both files exist and have equal readdates){similarly for filename/r is a string delimited by whatever characterimmediately follows the switch /s, e.g. filename/s\some text\. is any list of Alto executive commands separated by semicolons.Note that it is necessary to escape semicolons past the Executive command line reader.It is possible to nest Ifs by enclosing in braces ('{' and '}'): the braces will beremoved before the are passed to the Executive, but occurrences of " then "or " else " within the braces will not terminate the with respect to the outerIf.ЪН",ОpqТXН]Оg~rТiНІОbAsН1qТX Н*+sН2LqНІО^оsН1qН*+sН2LqН@О]KН2LНІОZпsТFН1qНЭОTюtqТXНЇОRhuv НґОPqТжwqП$ТвНґОN▄ТїП&Т╗П6НґОMТ≤ПUТ≥НґОK└Т┐П$Т└sqsqНґОJТН2ОG╗uНґОEQqТ≈П<Т≤НґОCмТ▐ПVТ░НёОAuxТНёО?ЯНёО>mНґО<qТ÷П7Т═sqНґО:▒ТН2О89uНґО5БqНЇО3┼uvН2О12uНёО.зxП2НґО,┐qxqП!x q НёО*+xН'qНёО(їxН'qП)xqНёО'#xН'qП)xqНёО%÷xН'qП)xqНёО$xН'qП2НёО"≈Н'ТЦТДП(НёО!НёО▐ТП0НёОПIНёО┤ПLНґО/xqТП'ТП)НґО╚ТП(xqНґОSx qП@НґОШТдПNТеНґОєТ▄П<Т█П"НґО Т°П>Т²НґО⌡Т°ПSТ²НґО РЭр8Яd <2Switches, "then", "else", and string matching all treat upper and lower case letters asequivalent.SemanticsIn the case that yields true the in the then clause (if present) arepassed to the Executive (via rem.cm) for execution, otherwise the in the elseclause (if present) are passed.In the case of the /s switch each occurence of the character * in the indicates awildcard to be matched by zero or more characters in the file. This also has to be escapedpast the Executive command line reader.EXAMPLES1.A quit macro in user.cm for achieving the example given in the Introduction is:M.QUIT:"*qDelete @4acacacacerrlogCompiler -p/c @4 If.run/r @4acacacacerrlog then Bravo/m @4acacacacac"This uses the MESA run switch /r.2.The equivalent of the example given in the Introduction for the BCPL world is:bcpl/f prog.bcplIf prog.bt/s:ERROR: then Bravo/b progString matching is needed since BCPL creates a .bt file whether or not there are errors.A quit macro in user.cm for achieving the above is:B.QUIT:"*qbcpl/f @4If @4acacacacbt/s:ERROR: then Bravo/b @4acacacacac"3.An extension of the above example to both load and run a successfully compiled programis:bcpl/f prog.bcplIf prog.bt/s:ERROR: then bravo/b prog ^ else bldr prog'; prog4.A further extension, which compiles the program only if it has been edited since last beingcompiled, is:If prog.bcpl/c>prog.br/c then bcpl/f prog.bcplIf prog.bt/s:ERROR: then bravo/b prog ^ else bldr prog'; prog5.A command file to edit file.bravo which may be held either locally or remotely:If file.bravo else Ftp Ivy retrieve/c file.bravoBravo/n file.bravo6.Of course the above example is good only for the specific file file.bravo. It makes bettersense in conjunction with the system Do.run (q.v.):If #1 else Ftp Ivy retrieve/c #1Bravo/n #1which can be used with a command of the form:Do edit file.bravoЪНN╟ОfЯqНґОbТшПLТэ НґО` Н2О^BuНґО[ЙqТ■ Т∙ПPНґОZfТ÷ПOТ═НґОXБТНґОV┼Т╙ПEТ╚НґОUТ█ПIТ▌НґОS┌ТП'НЇОQ+uvНюОNсqНґПOН(ОL{xqxН(ОJ╠qxОK>sОJ╠xОK>sОJ╠xОK>sОJ╠xОK>sОJ╠qН(ОHФxТхОIssОHФxОIssОHФxОIssОHФxОIssОHФxОIssОHФxОIssОHФxОIssОHФxОIssОHФxОIssН(ОGbxНґОE qТ sqНюОB╡НґП@sq Н(О@[xН(О>вП%НґО<qТаsqТбП,НґО:'ТП3Н(О7пx Н(О6KН(О4│О5sО4│xО5sО4│xО5sО4│xО5sО4│xО5sО4│xО5sО4│xО5sО4│xО5sО4│xО5sН(О2ЩxНюО0╔qНґТ ПVНґО/!Н(О,иxТН(О+EП'Н(О)аП&НюО'iqНґТ▐П#Т░П8НґО%ЕТН(О#▌xП.Н(О" П'Н(О ├П&НюО.qНґПOН(ОжxП0Н(ОRНюОЗqНґТ║Т╒П=НґОvТП3Н(ОxН(О⌡ Н═ОCqП-Н(О КxzЇ є=чZgjMATH TIMESROMAN TIMESROMAN TIMESROMANLOGO TIMESROMAN TIMESROMAN TIMESROMAN GACHA д√ ЪЪj/≥UЇ?ЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪЪif.bravo SwinehartJuly 9, 1982 9:05 AM