Perl

1. Perl Programming Language Design and Implementation (4th Edition) by T. Pratt and M. Zelkowitz Prentice Hall, 2001 Section 3.3.3 Appendix A.9

2. Perl overview • Perl (Practical Extraction and Report Language) is an interpreted language designed for efficient text-processing applications • It was developed by Larry Wall in 1986 • It was originally called PEARL, but a conflict with an existing graphics language resulted in the shortening of the name • The language includes pattern matching, file handling, and scalar data • It has syntax patterned after C and was originally designed to operate as a shell script • Its power is that it views programs and files as data • It has proven to be an effective language for interacting with Web pages

3. Perl structure • Variables in Perl are either integers or strings and begin with the symbol $. • A simple Perl program consists of a series of print statements. • It has the usual sequence of control structures such as for, while, and until loops and if conditional. • Perl shares an ability to process regular expressions like several other process languages • Example use: $ENV{'USER'} = ‘mvz’ • will be true if login name mvz is the string $ENV{'USER'} (i.e., is the user running this program). • This shows how Perl can interact with the system environment

4. Perl example 1 #!/usr/bin/perl 2 @inputdata = split(/ /, <STDIN>); 3 $count = 0; 4 foreach $nextone (@inputdata) 5 {print "$nextone"; 6 $count = $count + $nextone;}; 7 print "Sum = "; 8 print "$count\n"; Figure A.14 in text

5. Perl regular expressions • Perl provides a direct translation of regular expressions. • For example, the regular expression a+b+ is the following Perl script: • #!/usr/bin/perl # This is a Perl script • $_ = <STDIN>; # Read in input to argument $_ • if (/a+b+$/) then { print “yes\n”;} • else { print “no\n”;} # Match $_ with a+b+ • The pattern /X/ is matched against the string argument. • This pattern succeeds if the regular expression a+b+ extends from the initial character of the input line () to the end of the input line ($). • To succeed if a+b+ is contained within a string, we • only need the pattern /a+b+/.