Perl for Linguists

Michael Hammond

University of Arizona

Presentation materials:

• Presentation slides
• Summary of perl syntax
• Zipped examples

Various links:

• our free perl
• CPAN perl archive
• Perl.org
• a nice perl for older macs
• my web page
• My online replication of Bailey/Hahn
• Syllabification in OT, web interface
• Statistical NLP example programs
• Wall interview
• Perl poetry

Summary of perl syntax

1. Basic structure
• Statements. A program is composed of a list of statements. Each statement is terminated with a semicolon.
• Groups. Statements can be grouped together with curly braces into "statement groups".
2. Data types
• Strings are denoted with double or single quotes.
• Numbers have no special punctuation.
3. Variables
• Simple scalar variables are marked with a leading dollar sign, e.g. $myVar, $x, $a_long_variable_name, etc.
• Arrays are lists of related variables. The entire array is indicated with a leading @, e.g. @anArray, @myArray. Individual members of the array are referred to by index (starting at zero). The index occurs in square brackets and in that case the array is prefixed with a leading dollar sign, e.g. $anArray[0], $myArray[35], etc.
• Hashes are like arrays except that each element in the list has a name, rather than an index. The entire hash is indicated with a leading %, e.g. %myhash, %boringhashname, etc. Individual slices are referred to with a leading dollar sign and with the hash name in curly braces, e.g. $myhash{bob} $boringhashname{oranges}.
4. Some functions
• print(): prints something.
• localtime(): gets the local time.
• rand(): returns a random number.
• push(): adds something to the end of an array.
• pop(): returns the last element from an array (and removes it from the array).
5. Input-Output
• print(): prints something.
• open() and close(): creates a file handle from a file name and then closes the handle.
• < >: reads a line from a file handle.
6. Regular expressions
• Concatenation, e.g. /ab/ the string composed of a followed by b.
• Union, "or", e.g. /a(b|cd)e/ the string abe or the string acde.
• Kleene star, "any number of", e.g. /ab*c/ the strings ac, abc, abbc, abbbc, etc.
• variable =~ /regular-expression/: true if the variable matches the regular expression.
• variable =~ s/regular-expression/string/: replaces the first instance of the regular expression by the string.
7. Control structures
• if (condition) {statement group}: conditional application. If the condition is true, the statement group gets a chance to apply.
• while (condition) {statement group}: conditional iteration. As long as the condition remains true, the statement group keeps applying.
• for (initialize; end-condition; iteration) {statement group}: quantified iteration. The statement group iterates a specified number of times.
• foreach variable (list) {statement group}: list iteration. The statement group iterates once for every element of the list.
8. Object-oriented programming
• Object-oriented programming involves creating objects. Each object has functions/methods and data that it uses to interact with other objects.
• new(): The typical name for the method that creates some object. For example, $mybug = Bug->new() would create a new object of the Bug class and assign it to the variable $mybug.
• ->: Object methods and data are usually referred to with the dereferencing extractor, e.g. $mybug->{thestring} would refer to a string within the object held in $mybug. Something like $mybug->doit() would call the doit() method of the Bug class.
• @ISA: Objects can inherit data and methods from other objects. Parent objects are indicated as members of this array.