1. Introduction to Perl: Practical extraction and report language
Origins
Nature of Perl
Characteristics of Perl
Example

2. What is Perl?
Includes most powerful constructs from predecessor languages (sh, awk)
From awk (text file processing utility)  Designed to write short programs to process text files, using pattern matching to produce reports of results
From UNIX sh, csh process creation and destruction

3. What is Perl?
Added sockets  networking language to support communication with other processes and languages
Added modules and OOP
Added constructs  expressive, flexible language

4. History Release 1.000 1987 designed by Larry Wall
Began as UNIX tool, but has spread
Popularity increased in 1990s
Portable systems programming language
Easily obtained and free
Useful for Common Gateway Interface (CGI) programming for WWW

5. Language and Programs
Simple language – a beginner can write small useful programs
Complex language – has a richness and power to perform sophisticated tasks
Easy language to learn if you know C, sh or awk
Practical (easy to use, efficient, complete), but not beautiful
Be disciplined, follow standards  PERL programs will be readable

6. Scripts vs Programs Early OS/UNIX sh:
Small sequence of commands repeatedly typed  put into files and interpreted
Hence scripts
Perl evolved from shell languages
But Perl “scripts” are first compiled into intermediate language before interpreted
Hence Programs

7. Central Characteristics
Implicit variables - defined by language implementation, not defined by user, but accessible
Variables are implicitly declared – type is inferred by compiler based on name syntax or context
Numbers are numbers - one numeric type, same as double (all literals and operations implicitly converted to this type)
Strings and numbers – implicit type conversions
No unnecessary limits – strings and arrays implicitly grow

8. Central Characteristics
Scalar and list context
Array var when scalar expected  length of array
Scalar var when array expected  array of 1 element
Interchangeability of functions and operations
Ex. list operators in which op is followed by operands
Ex. Functions have () around operands, but can omit ()
More than one way to do it
Simple techniques and more complex, elegant alternatives

9. Getting Perl www.activestate.com or My CD Four directories needed:
doc – Perl doc (manpages)
src – source code files for Perl
ports – subdirectories and symbolic links for
implementations of Perl not supported by
standard distribution
scripts – collection of example Perl programs

10. Other tools Editor – NTEmacs free
Debugger – see ActiveState debugger

11. Example Program
To see listing of environment variables on your computer available to the program
#!/usr/local/bin/perl
foreach $key (keys (%ENV)) {
print qq | The value of $key is ENV{"$key"}\n|; }

12. Running Example Program
Save as with .pl extension
At command prompt type filename.pl
For verbose warnings type perl –w filename.pl
To run with debugger perl –d filename.pl