Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 121Subroutines3-29-20102Opening Discussion■Do you have any questions about assignment #6?3Regular 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///.4Binding for RegExs■By default a regular expression will happen on the variable $_. To make it happen on something else use the binding operator, =~.5Calling Subroutines■The syntax of calling a subroutine is very much like the syntax of calling a function in C. We give the name of the subroutine followed by an argument list in parentheses.■In Perl the parentheses are optional in some cases. (Definitely when there are no arguments.)■Older Perl implementations required a & in front of the subroutine name. Only a few usages would require that now.■Subroutines can be called before they are defined in Perl.6Writing Subroutines■A subroutine in Perl looks like the following:sub name {➔statements}■Note the lack of an argument list. Instead, the variable @_ will contain the arguments passed in.■The my statement can be used to declare local variables. This is also how we get values out of @_. Note that Perl allows list assignments for this purpose.■A return statement allows you to return values from a subroutine.7Passing Arguments■By default, Perl passes arguments by value.■The argument list is a list of scalars. Passing things other than scalars leads to flattening.■You can pass a reference by putting \ in front of the variable you are passing at the point of the call.■When using a reference in the subroutine you have to prepend the type of what you are pulling out in front of the variable name. So you get things like $$i, @$a, %$h, or $$a[5].8Strict■To make it so that Perl will force you to declare variable put the following line at the top of your program.use strict;■It is also a good idea to add the following line at the top of your code.use warnings;9Command-Line Arguments■When you run a Perl program, any arguments specified on the command line are put in a variable called @ARGV■As a bonus, the $0 variable stores the name of the program.10Modules and Libraries■For subroutines that you will want to reuse often it can be helpful to put them into a separate file.■It is common to name these files with .pm and the last line of the file needs to be 1;■Inside your other programs the use keyword allows your code to use your module.11Perl Debugger■If you run Perl with the -d option it will go into an interactive debugging mode.■You can force this by adding it to the #! at the top of the program or using perl -d from command line.■The command q will stop the debugger. h and h h give help.12Closing Remarks■We have a quiz on Perl next class.■Assignment #6 is due on
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