1Flow Control and Basic RegExs3/31/20082Opening Discussion■Do you have any questions about anything?■I've redone the schedule to reflect content in the book we are using and spread it out to fit our needs.■Notes on peer review panels and different systems.NASANSFNIH3Conditionals in Perl■Perl has the standard if statement that you are used to.Use the normal comparison operators for numbers.For string data you use letter symbols. Use eq for equality.■The if can follow a single statement.■Format with if in front requires curly braces so they have elsif.■There is also an unless that works like if, but the action happens when it is false. This exists because Perl programs don't like to use not.■Boolean operators and, or, not are in English, not symbols. Short circuit so can be used for flow control.4Loops in Perl■Perl has a full compliment of loops. Most are just like what you are used to in C family language.■while loop is the same.■do-until instead of do-while.■for loop is the same.■for each loop is different and goes through the elements of a list. We saw how to use that one last class.5Writing Files■We saw how to use open to open a file for reading and then how to read from it.■If you precede the file name with a “>” the handle will be for writing. (It's like directing output of a program to file in Linux.)■That deletes and existing file. Use “>>” to append. (Also like Linux.)■The file handle becomes the first argument to print. There is no comma after the handle.6Regular Expressions■Regular Expressions are a really big deal in Perl. They are a significant part of why so many people use Perl.■Regular expressions can be used with several types of operations.■Matching – put the matching expression between matched symbols, typically //.■Substituting – The normal format is s/// where after the first / you put the expression to match and after the second / is what to replace it with. Put a g at the end to substitute multiple. An i to ignore case.■Transcription – replace chars using tr///.7Binding for RegExs■By default a regular expression will happen on the variable $_. To make it happen on something else use the binding operator, =~.8Closing Remarks■I think you know enough Perl to take a quiz now so we will have quiz #4 next
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