Perl Tutorial. Diana Inkpen. School of Information Technology and Engineering University of Ottawa. CSI 5180, Fall 2004

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1 Perl Tutorial Diana Inkpen School of Information Technology and Engineering University of Ottawa CSI 5180, Fall What is Perl Practical Extraction and Report Language. Created, implemented, maintained by Larry Wall. Interpreted language that is optimized for string manipulation, I/O, and system tasks. Syntax elements from the C, Bourne shell, csh, awk, sed, grep. (Unlike other interpreted languages, Perl compiles and optimizes the code before running.) 2

2 Some of Perl s many strengths Speed of development edit a text file and just run it. No separate compiler needed. Short pieces of code that do a lot (magic operators). Power Perl s regular expressions, easy file handling and data manipulation. Flexibility freedom of expression. Portability Perl compilers for all platforms. Extensibility modules available on CPAN. Price free. Extra: it is fun!! 3 The Hello, world program! #"$% % '&( )*+-, How to run the program written in the file myfile : chmod u+x myfile or myfile perl -w myfile 4

3 Basic syntax Perl is free form whitespace doesn t matter (but better use indentation for readability). All Perl statements end in a ; (semicolon), like C. Comments begin with # (pound sign) and last until the end of line (no multi-line comments). Variable names start with $ (or, %). 5 More programs (!! ' -, - #, -,! " )*+-, (!! '! *, -, -, - #, -,! " )*+-, 6

4 Variables Don t need to declare variables, but better to declare them (, -#, ). Cannot declare type (clear from context). Scalars Numbers Strings Arrays of scalars Hashes (associative arrays of scalars) 7 Strings Single-quoted strings.! ) ) )! & Double-quoted strings.! )!! & Interpolation takes places only in double-quoted strings. 8

5 Scalar variables Hold a single scalar value (number, string, or reference). Begin with $, followed by letter, then possibly other letters, digits, or underscores.! *, &'% -, *! *, -, 9 Numerical operators! *,,,, *- ' *, #, " - & -! #,! " ", # " " " 10

6 Comparison operators (1) - -!! * *! *! '% * '% *! %! 11 Comparison operators (2)! *,,,, '%, '%, '%! -, & -, &, '% &, '%! -, '% 12

7 String operators Concatenation ( Hi. there ;)! *, ' #,! ', # #! * ' -, - - % )+, * &! *!' % )+-, 13 Variable interpolation -,, * & )*+-, * % * & * & )*, * &! ) Interpolation only in double-quoted strings 14

8 Print: A list operator Accepts a list of things to print, separated by commas. & - '!& * -"! " ' *!!& " " * & ' )+, & - '!& * % ' % %*- & % & - )*+-, %! -, #, % )! )*+-, % )! " " )+, ) )+, 15 Arrays An array is an ordered list of scalar variables. - +, - -" + " -" + "!,!-* ) -!!)*+-, %*!- - ) -, &!- - ) -,!! "! - "! *!) -,, )*+-, - --,! * -* - ) -, 16

9 Functions for arrays! *, #" (", " ", ", " " " *, " " ", " " #", #" " * % -, - ", "$ % "$ " --",!)*+-, % * 17 Hashes,,, " &,,, A hash is an associative array. A hash is a list of keys that have values. * * -"! *+ & % & *-, &! & & &! & % &! & % 18

10 Control structures IF (1), - *, - *!& &- - *,! -, 19 IF (2). Boolean values,, -, -, * -, -!! Boolean values False is 0,, 0, or undef. True is anything else. 20

11 Control structures WHILE!!, * %!! #,!!,, last; and next; 21 Control structures FOR!,,, *!! &!!,, * ), -!,, * )*+, 22

12 Control structures FOREACH!,,! )+-,! )+, 23 Basic I/O,!& -! %!! %&! * &!!,,!!- )+,,!&,!& %! ' %&! & ) -" " ", 24

13 Defaults is the name of the default scalar variable! % )+,!! #,!!, 25 Regular expressions (R.E.) (1) A regular expression describes a set of possible strings. - * -,!! * #,,!! * #, 26

14 R.E. (2) Single-character matching *, " "!, * & ) &, * &, * '!, " *! * * ) " ) & & " * % )* % &! " %! )! "!! ) )%)*) ) ) ) ' * - 27 R.E. (3) Grouping patterns Sequence ( *! ) Alternation (!, ) Multiplication *! +, " " *%! +, " "! -!! -!! *! -' & *! -!!! -'- " % * *& 28

15 Pattern-matching operators (4) not match operator *,! - -'- ' * - -- * & - ) ' * %! & ) " - ) %* &!!! * & -* *-! *! interpolation!, 29 R. E. (5) Anchoring patterns &) ' & ' &! -'! %!& ' ' *&!& ) ' %! & & ) ' * %! & & ) ' ) ' *& - % '& - - % '& -'- 30

16 R. E. (6) Returning matches &, " * *&, * &,,, ",, ', ' &, 31 Substitutions ' % - *' % - ' %! *' *-! * -!& * *+,, + ' +-,!!,! +-,! )*, *! *! * ' -, 32

17 Translations % - % *- * % & -,, *!,, ** #, **, #" *!, 33 Subroutines (1) '! ) -, & & ' %,!, ', & &, ",, ', 34

18 Subroutines (2),! ',! & & % ", & & " #" ", & & #, ', & & ' % ', 35 Filehandles STDIN, STDOUT, STDERR, ** " & & & * & &, ** " %! & * ' *!! -,!!,,,!!, 36

19 6 Formats (1)! " " #%$&&"&&&&&&&&&"&&&&&&&&&&&&& # '( )* #%$&&"&&&&&&&&&"&&&&&&&&&&&&& # ' +"+ #%$&&"&&&&&&&&&"&&&&!$&$&&&&,# ' -.0/1' + 2/3'4 5 " " 7( ( 8 :9<;; =>?7@ Ä BB!+C* EDF>=:9G H "( I9KJL9NM=>>O P P B +F :9NQ=Q=RA -FS! ( :9G -FSL9KJ"T:9NMMMU- 37 Formats (2) (5 WVK " "0/FXFY"B(U) B +XZ[#"#\ EX^] ( )_- `B(U B +R':abX*c (5 WVK0/dXF exzf##\ gx^] (?(5 _!':abx*c h B" ivj&ÿ Z k`- 5Wc!B Vj'( * 2/3' +"+l/3' -.0/3' + m/3'4 ^5eZn!+5)B!o09Komc h pvn "*Zqcr HS R R ( s - B + 2VK "*Zect- B + 2VN*Zec "" #u7f 8 # #\;; =">v7@ ABBv+C _D(>= # #w H ( J(?M=>>O,# "" 38

20 6 Z 6 Z Context considerations 5 ++ ( r] ( HB(C) + V V ' +- B +- B RHB(C n B r _' +-B $. B + vb +! HB(C + ^ _ )Z B _?$. $. +- B RBd C U! ` B" F* +`?$. + * v +R'. ED"Z '. N' r+- B v'r B F*? `$. '. +- B!+CU+- 5? vb +` B" F* r?$. XF' +- BeX X$.eX +- B0V 5 +- B0V 5 `+ ^ 8_- F 8`?- (!?' +"- B `+ ^ 8_- F 8` v B" * + `$.0/ + 5) U.r+5)- + ) + B + B +(? `B ) 8 S.+R( H B(C + ) + '() +)k's +- B B" F* v ) + h! S.!!' 39 Command line arguments, &,,,,,,! *! * '! % * * '% *!!! -"!! ) -, *!& &! *!& & " * " * 40

21 Optimization for speed Perl procedure calls are expensive, especially if you re passing in arrays or hashes. So feel free to inline subroutines called within a tight loop. It s not as nice a programming style, but the performance gain is worth it. You should put comments in the code, however, indicating where you re doing this and that speed gain is the reason for it. Use hashes instead of arrays when possible. 41 Perl hints to be used in A1 to A3 Write readable code! Perl will let you write cryptic code, but Perl code does not have to be cryptic. Use the -w flag. It will give you many warnings that almost always point out errors in your code. (but slower) Use use strict; at the beginning of your code. It forces you to declare your variables and gives you error messages which, once fixed, make your code easier to read. Read Ch.8 of Programming Perl, Common Goofs for Novices, Efficiency and Programming with Style. 42

22 References Schwartz, Randal L. and Christiansen, Tom, Learning Perl, second edition, O Reilly, Wall, Larry; Christiansen, Tom; and Schwartz, Randal L., Programming Perl, third edition, O Reilly, Perl Tutorial Introduction to Perl things/instruction/perl/perlcourse.html Picking Up Perl, a Freely Redistributable Perl Tutorial Book 43