Introduction to Perl

Introduction to Perl

What is Perl? • Practical Extraction and Report Language • 实用摘录与报告语言 • Pathlogical Eclectic Rubbish Lister • 反常，折中的垃圾陈列器

What is Perl? • Perl is a Portable Scripting Language • No compiling is needed. • Runs on Windows, UNIX and LINUX • Fast and easy text processing capability • Fast and easy file handling capability • Written by Larry Wall • “Perl is the language for getting your job done.”

How to Access Perl • Off the school network • Located on the 100.10 machines at: /usr/local/bin/perl • To install at home • www.perl.com Has rpm's for Linux • www.activestate.com Has binaries for Windows • Latest Version is 5.8 • To check if Perl is working and the version number • % perl -v

The Basic Hello World Program • Program: #!/usr/local/bin/perl -w print “Hello World!\n”; • Save this as “hello.pl” • Give it executable permissions • chmod ug+x hello.pl • Run it as follows: • ./hello.pl

“Hello World” Observations • “.pl” extension is optional but is commonly used • The first line “#!/usr/local/bin/perl” tells UNIX where to find Perl • “-w” switches on warning : not required but a really good idea

How to use Perl • Syntax • A Web Server Example

要记住，过早的优化往往是错误的根源。如果您在 Perl 中写了一个原型，并用其他语言来重写是没有问题的。原型意味着能够方便地开发。

Perl 解释器 • 速度和 Benchmark • Perl 的容错能力

Perl 的缺憾 • 速度算法，内置函数 • 训练 • 面向对象 • 线程以及统一字符编码

Perl 的优势 • 某些方面的优势，例如： • 正则表达式 • 隐含的函数声明 • 不严格的语法 • 象日用文档似的程序结构 • 通用的灵活，大大减少开发的时间 • 几乎没有任何 C 或 C++ 能做而 Perl 不能的事情

Syntax • Literals • Types of Variables • Operators • String Functions • Loop

Numerical Literals • Numerical Literals • 6 Integer • 12.6 Floating Point • 1e10 Scientific Notation • 6.4E-33 Scientific Notation • 4_348_348 Underscores instead of commas for long numbers

String Literals • String Literals • “There is more than on way to do it!” • 'Just don't create a file called -rf.' • “Beauty?\nWhat's that?\n” • “” • “Real programmers can write assembly in any language.” • Quotes from Larry Wall

Types of Variables • Types of variables: • Scalar variables : $a, $b, $c • Array variables : @array • Hash variables : %hash • File handles : STDIN, SRC, DEST • Variables do not need to be declared • Variable type (int, char, ...) is decided at run time • $a = 5; # now an integer • $a = “perl”; # now a string

Operators on Scalar Variables • Numeric and Logic Operators • Typical : +, -, *, /, %, ++, --, +=, -=, *=, /=, ||, &&, ! ect … • Not typical: ** for exponentiation • String Operators • Concatenation: “.” - similar to strcat $first_name = “Larry”; $last_name = “Wall”; $full_name = $first_name . “ “ . $last_name;

Equality Operators for Strings • Equality/ Inequality : eq and ne $language = “Perl”; if ($language == “Perl”) ... # Wrong! if ($language eq “Perl”) ... #Correct • Use eq / ne rather than == / != for strings

Relational Operators for Strings • Greater than • Numeric : > String : gt • Greater than or equal to • Numeric : >= String : ge • Less than • Numeric : < String : lt • Less than or equal to • Numeric : <= String : le

String Functions • Convert to upper case • $name = uc($name); • Convert only the first char to upper case • $name = ucfirst($name); • Convert to lower case • $name = lc($name); • Convert only the first char to lower case • $name = lcfirst($name);

If ... else ... statements • Similar to C/C++ - except the scope braces are REQUIRED!! if ( $os eq “Linux” ) { print “Sweet!\n”; } elsif ( $os eq “Windows” ) { print “Time to move to Linux, buddy!\n”; } else { print “Hmm...!\n”; }

Unless ... else Statements • Unless Statements are the opposite of if ... else statements. unless ($os eq “Linux”) { print “Time to move to Linux, buddy!\n”; } else { print “Sweet!\n”; } • And again remember the braces are required!

While Loop • While loop: Similar to C/C++ but again the braces are required!! • Example : $i = 0; while ( $i <= 1000 ) { print “$i\n”; $i++; }

Until Loop • The until function evaluates an expression repeatedly until a specific condition is met. • Example: $i = 0; until ($i == 1000) { print “$i\n”; $i++; }

For Loops • Like C/C++ • Example : • for ( $i = 0; $i <= 1000; $i++ ) { print “$i\n”; } • Another way to create a for loop • Example • for $i(0..1000) { print “$i\n”; }

Minimal Perl Web Server(1) #!/usr/bin/perl use Socket; use Carp; use FileHandle; # (1) use port 8080 by default, unless overridden on command line $port = (@ARGV ? $ARGV[0] : 8080); # (2) create local TCP socket and set it to listen for connections $proto = getprotobyname('tcp'); socket(S, PF_INET, SOCK_STREAM, $proto) || die; setsockopt(S, SOL_SOCKET, SO_REUSEADDR, pack("l", 1)) || die; bind(S, sockaddr_in($port, INADDR_ANY)) || die; listen(S, SOMAXCONN) || die;

Minimal Perl Web Server(1) # (3) print a startup message printf(" <<<Type-O-Serve Accepting on Port %d>>>\n\n",$port); while (1){ # (4) wait for a connection C $cport_caddr = accept(C, S); ($cport,$caddr) = sockaddr_in($cport_caddr); C->autoflush(1); # (5) print who the connection is from $cname = gethostbyaddr($caddr,AF_INET); printf(" <<<Request From '%s'>>>\n",$cname);

Minimal Perl Web Server(1) # (6) read request msg until blank line, and print on screen while ($line = <C>) { print $line; if ($line =~ /^\r/) { last; } } # (7) prompt for response message, and input response lines, # sending response lines to client, until solitary "." printf(" <<<Type Response Followed by '.'>>>\n"); while ($line = <STDIN>) { $line =~ s/\r//; $line =~ s/\n//; if ($line =~ /^\./) { last; } print C $line . "\r\n"; } close(C); }

Resources For Perl • Books: • Learning Perl • By Schwartz • Published by O'Reilly • Programming Perl • By Larry Wall,Tom Christiansen and Jon Orwant • Published by O'Reilly • Web Site • http://safari.oreilly.com • Contains both Learning Perl and Programming Perl in ebook form

Web Sources for Perl • Web • www.perl.com • www.perldoc.com • www.perl.org • www.perlmonks.org

Thank you 

Introduction to Perl