code used in this book, web site for URLs code in this book Wall, Larry Llama book footnotes in this book portability Perl portability and Unix portability and exercises in this book Wall, Larry Larry Wall, Larry Perl Practical Extraction and Report Language Perl programming languages low-level vs. high-level low-level programming languages high-level programming languages Camel book Programming Perl resources for further reading Programming Perl functions defaults for defaults shortcuts portability Perl portability and high-level programming languages Perl current trends in Perl reasons for using/not using Perl obtaining licenses for Perl Perl licenses for CPAN (Comprehensive Perl Archive Network) Comprehensive Perl Archive Network CPAN URLs CPAN URLs search interfaces for Perl Perl support for support for Perl bugs in Perl Perl bugs in documentation for Perl Perl documentation for manpages Programming Perl as documentation for Perl Camel book Llama book quick reference to Perl Vromans, Johan newsgroups for Perl mailing lists for Perl Perl mailing lists and newsgroups for comp.lang.perl.moderated newsgroup Perl Monastery URLs Perl Monastery perlbug utility bugs in Perl reporting Perl bugs in reporting utilities perlbug utilities Unix Unix, utilities for programming text editors programming text editor for emacs text editor vi text editor word processor, using instead of a text editor text mode ASCII mode binary mode `Hello, world' program filename extensions file extensions .plx file extension chmod command (Unix) ./ dot and slash dot and slash (./) slash with dot (./) whitespace comments # pound sign pound sign (#) in comments block comments #! line /usr/bin/perl /usr/local/bin/perl #!perl perldiag manpage main program variables declaring semicolon (;) ending expressions ; semicolon semicolon \\\\n shortcut backslash escapes compiling code code compiling bytecodes runtime Web running programs over programs running over the Web Internet Web programs example of in a nutshell #! line ` ` backquotes/backticks backquotes/backticks (` `) enclosing external commands perldoc command @lines array variable angle brackets angle brackets () scalars numbers numbers integers double-precision floating-point values internal integers integer pragma pragmas integer literals floating-point literals integer literals _ underscore underscore (_) in integer literals nondecimal integer literals octal literals leading zero hexadecimal literals numeric operators operators numeric + addition operator addition operator (+) - subtraction operator subtraction operator (-) * multiplication operator multiplication operator (*) / division operator division operator (/) % modulus operator modulus operator (%) ** exponentiation operator exponentiation operator (**) strings strings characters NUL character string literals literal strings string literals single-quoted string literals ' ' single quotes single quotes (' ') enclosing strings \\\\ backslash backslash (\\\\) \\\\n shortcut within a single-quoted string double-quoted string literals double quotes ("") enclosing strings "" double quotes double quotes backslash escapes list of string escapes backslash escapes variable interpolation double-quoted string literals variable interpolation and string literals double-quoted double-quoted string literals strings operators for . operator x string repetition string repetition operator (x) numbers converted automatically to strings strings converted automatically to numbers warnings error messages -w option perldiag manpage warnings explained in lexical warnings perllexwarn manpage variables dollar sign ($) in scalar variable names Perl identifiers names of variables choosing lowercase vs. capitalization in variable names capitalization vs. lowercase in variable names uppercase vs. lowercase in variable names assigning scalars values scalar, assigning to variables scalars values of, assigning to variables variables assigning scalar values to = assignment operator assignment operator (=) variables altering binary assignment operators . string concatenate operator string concatenate operator (.) .= append operator append operator (.=) **= raise to the power of operator raise to the power of operator (**=) print function variable interpolation double-quoted string literals scalar variables, interpolating into variable interpolation double-quote interpolation variable interpolation dollar sign ($) in regular text text regular dollar sign in $ dollar sign dollar sign names of variables enclosed in curly braces variables names of enclosed in curly braces curly braces ({ }) enclosing variable names { } curly braces curly braces precedence operators precedence and associativity operators associativity and operator precedence precedence parentheses indicating precedence ( ) parentheses parentheses precedence table of associativity chart of maintenance programmers writing intelligible code for numeric comparison operators numbers comparison operators for comparison operators operators comparison string comparison operators strings operators for comparison operators for if control structure else keyword curly braces ({ }) block, enclosing code code curly braces enclosing block curly braces curly braces, block Boolean values as handled by Perl negation (not) operator (!) ! negation operator negation operator not operator negation operator operator line-input operators line-input operators standard input chomp operator newlines trailing chomp operator for removing loops endless, stopping endless loop, stopping control structures stopping endless loops created by while control structure code while control structure for repeating blocks of loops curly braces ({ }) block, enclosing code code curly braces enclosing undef value variables undef value and string accumulator operator defined function and defined function undef operator lists arrays elements indexing elements subscripts array elements elements of an array array indices negative array indices list literals .. range operator range operator (..) qw shortcut lists qw shortcut for whitespace quoting qw shortcut form of delimiters in lists values list, assigning to variables variables assigning list values to assigning lists @ at-sign at-sign(@) indicating arrays references pop operator elements pop and push operators for parentheses optional use of push operator unshift operator shift operator double-quoted string literals arrays, interpolating into $" variable email addresses, compile time errors and foreach control structure default variable ($_) $_ default variable default variable reverse operator sorting sort operator for ASCIIbetical order, sort operator for scalar context list context expressions context and context context scalar context forcing operator context and end-of-file/end-of-input subroutines system functions user functions subroutines subroutines defining sub keyword body of subroutine subroutines invoking & ampersand ampersand (&) in subroutine names subroutines calling invoking subroutines return values void context context void list context return values and wantarray function arguments @_ array variable parameter lists argument lists parameter lists &max subroutine lexical variables private variables lexical variables my operator creating lexical variables with scoped variables lexical variables subroutines lexical variables in semicolon (;) return value expressions and local operator variables value of, saving values saving using local operator stacks my operator using instead of local operator parameter lists variable-length variable-length parameter lists &max subroutine parameter lists empty lexical variables scope of variables my operator use strict pragma restrictions pragmas _ underscore underscore (_) in variable names return operator & ampersand ampersand (&) omitting functions builtin, ampersand and builtin functions ampersand and modules prototypes hashes associative arrays hashes hash keys keys hash keys key-value pairs hashes reasons for using names hashes and IP addresses, hashes and word count, hashes and databases hashes and hashes accessing elements of hash elements, accessing curly braces ({ }) enclosing hash keys names of hashes hashes names of dollar sign ($) preceding hash names curly braces ({ }) following hash names Flintstones illustrating hash names percent sign (%) indicating entire hash unwinding hashes hashes unwinding assigning hashes hashes assigning => big arrow big arrow (=>) arrows -> little arrow little arrow (->) , comma comma (,) hashes functions for hash functions keys function values function each function while control structure using each function with exists function hash keys exists function for checking delete function hash keys delete function for removing hashes elements of, interpolating into double-quoted string literals double-quoted string literals hash elements, interpolating into backslash escapes input/output (I/O) I/O (input/output) input/output (I/O) I/O (input/output) input standard input while control structure shortcut for input while control structure shortcut for operator while loop shortcut and default variable ($_) input stored in diamond operator () input reading with diamond operator diamond operator diamond operator Wall, Heidi Unix utilities for diamond operator and invocation arguments - hyphen hyphen (-) indicating standard input stream line-input operators $ARGV variable diagnostic messages, from diamond operator\\ `wimla,' diamond operator and invocation arguments @ARGV array diamond operator () @ARGV array and argc $0 variable output standard output standard output print function output and arrays interpolating vs. printing double quotes ("") arrays and print function newlines and newlines print function and buffered output output buffered flushed buffer buffer flushing of print function optional parentheses and parentheses optional use of with print function function calls, parentheses and output formatted with printf function printf function formatted output conversions percent sign (%) indicating conversion % percent sign percent sign percent sign (%) %g conversion general numeric conversion %d conversion decimal integer conversion decimals rounding printf function and %s conversion %f conversion floating-point conversion percent sign (%) printing arrays printf function and x string repetition string repetition operator (x) regular expressions Unix utilities for regular expressions and patterns patterns grep command (Unix) regular expressions and Flintstones illustrating Unix grep command globs .pm files patterns Ú Ú forward slashes forward slashes (Ú Ú) enclosing a pattern metacharacters dot (.) as wildcard character matching with dot wildcard character . dot dot period dot * star star (*) as quantifier quantifiers + plus sign plus sign (+), as quantifier ? question mark question mark (?) as quantifier parentheses grouping patterns with \\| vertical bar vertical bar (\\|) patterns test program for [ ] square brackets square brackets ([ ]) in pattern test program results downloading pattern test program character classes [ ] square brackets square brackets ([ ]) in character classes - hyphen hyphen (-) specifying range of characters shortcuts character class \\\\d shortcut digits, \\\\d shortcut for \\\\w shortcut words, \\\\w shortcut for \\\\s shortcut whitespace \\\\s shortcut for spaces \\s shortcut for spaces shortcuts negating negating shortcuts \\\\D shortcut \\\\W shortcut \\\\S shortcut quantifiers numbers comma-separated curly braces ({ }) indicating quantifier anchors ^ caret anchor caret anchor (^) indicating beginning of string dollar sign ($) indicating end of string \\\\b word-boundary anchor word-boundary anchors \\\\w characters Flintstones anchors and \\\\B nonword-boundary anchor parentheses with memory function memory parentheses regular expression memories backreferences \\\\ backslash backslash (\\\\) in backreferences Flintstones illustrating backreferences memory variables precedence Flintstones precedence and perlre manpage perlrequick manpage perlretut manpage patterns manpages for regular expressions using m// operator pattern match operator (m//) matching with m// operator delimiters nonpaired nonpaired delimiters Ú Ú forward slashes forward slashes (Ú Ú) vs. m// operator option modifiers flags /i modifier case-insensitive matching, /i modifier for matching with /i modifier dot (.) as wildcard character /s modifier and /s modifier characters matching with /s modifier matching with /s modifier =~ binding operator binding operator (=~) matching with =~ binding operator default variable ($_) =~ binding operator and grep command (Unix) writing Perl program resembling match variables variables match memory, persistence of builtin variables variables builtin automatic match variables $& variable $` variable $' variable performance, slowed by automatic match variables programming automatic match variables and s/// substitution operator matching with s/// substitution operator s/// substitution operator vs. m// operator m// operator vs. s/// substitution operator /g modifier, s/// substitution operator and global replacements whitespace global replacements and delimiters changing for s/// substitution operator /i modifier s/// substitution operator and /s modifier s/// substitution operator and binding operator (=~) s/// substitution operator and case shifting characters case shifting and uppercase case shifting and lowercase case shifting and capitalization case shifting and \\\\U shortcut \\\\L shortcut \\\\E shortcut \\\\l shortcut \\\\u shortcut split operator whitespace split operator and patterns split operator and join function split operator vs. join function control structures unless control structure if control structure unless control structure and negation (not) operator (!) else clause, using with unless control structure if control structure else clause and maintenance programmers writing intelligible code for programming while control structure until control structure for reversing until control structure expressions modifiers for if modifier code reading unless modifier until modifier while modifier foreach modifier while modifier until modifier unless modifier foreach modifier naked block control structure while control structure naked block control structure and foreach control structure naked block control structure and scope of variables naked block control structure and sqrt function perlfunc manpage elsif clause perlfaq manpage ++ autoincrement operator autoincrement operator (++) -- autodecrement operator autodecrement operator (--) scalar variables autoincrements/autodecrements for preincrements/predecrements postincrements/postdecrements hashes autoincrements/autodecrements and for control structure while control structure for control structure and continue block perlsyn manpage foreach control structure vs. for control structure for control structure vs. foreach control structure semicolon (;) in for/foreach control structures loop controls control structures loop controls for programming languages structured last operator code last operator for exiting early programs last operator for exiting early programs code __END__ marker loop blocks iterations, next and redo operators for next operator continue block perlsyn manpage continue block and loop blocks redo operator loop blocks labels for labels logical operators Boolean values logical operators for && operator AND operator (&&) OR operator (||) || operator OR operator "short-circuit" logical operators values of short-circuit logical operators C programming language operators and programming languages C, operators and ?\: ternary operator ternary operator (?\:) if-then-else test, ternary operator for partial-evaluation operators control structures partial-evaluation operators for maintenance programmers partial-evaluation operators and && operator AND operator (&&) OR operator (||) negation (not) operator (!) xor operator precedence partial-evaluation operators and filehandles I/O (input/output) filehandles and input/output (I/O) filehandles and STDIN filehandle standard input stream standard output stream STDOUT filehandle Unix input/output and perlport manpage, standard input/output and | pipe pipe (|) standard error stream STDERR filehandle filehandles opening/closing open operator < less-than sign less-than sign (<) for opening files > greater-than sign greater-than sign (>) for creating files log files, filehandles and whitespace greater-than sign and close operator filehandles bad bad filehandles end-of-file/end-of-input bad filehandles and warnings bad filehandles and die function fatal errors die function for errors fatal errors error messages printed by die function exit status make utility, exit status and programs exit status and $! variable programs name of die function and line number die function and chunk number, die function and newlines trailing die function and trailing newlines newlines, trailing $0 variable _ _FILE_ _ and _ _LINE_ _ tokens caller function OR operator (||) die function and warn function warnings warn function for programs name of warn function and line number warn function and filehandles using line-input operators print function filehandles and printf function filehandles and filehandles default for output, changing defaults output filehandle STDOUT filehandle select operator buffer flushing of log files, filehandles and filehandles reopening STDERR filehandle error messages sending to a file files tests for filehandles tests for files tests for list of filehandles tests for list of symbolic links resources for further reading file tests parentheses file tests and files links to, finding with stat function user-ID (uid) uid (user-ID) stat function scalar variables stat function and stat(2) manpage $dev (device number) $ino (inode number) $mode $nlink (number of links) links number of ($nlink) user-ID, numeric ($uid) $uid user-ID, numeric numeric user-ID user-ID, numeric group-ID ($gid) $gid group-ID $size files size of, scalar variable for finding $atime (timestamp) $mtime (timestamp) $ctime (timestamp) timestamps system time Epoch symbolic links lstat function localtime function timestamps number for, converting gmtime function Universal Time Greenwich Mean Time time function bitwise operators bitstrings perlop manpage bitwise operators and resources for further reading bitwise operators stat buffer buffer stat stat function underscore filehandle and lstat function underscore filehandle and _ filehandle underscore filehandle filehandles underscore directories manipulating chdir operator working directory chdir operator for changing cd command (Unix) home directory ~ tilde-prefix tilde-prefix (~) globbing echo command glob operator angle brackets angle brackets () filename globbing and globbing vs. filehandle reading filehandles reading, vs. globbing indirect filehandle read readline operator directory handles opendir operator readdir operator closedir operator files names of, directory handles for reading globbing vs. directory handles recursive directory listing File\:\:Find library files manipulating files removing removing files rm command (Unix) unlink operator glob operator combining with unlink operator permissions Unix and files renaming rename function mv command (Unix) .old files, renaming to .new files .new files, renaming from .old files links Unix model of files/directories and mounted volume inodes directories dot (.) indicating current directory .. dot-dot dot-dot (..) indicating parent directory link count link function symbolic links symbolic links soft links soft links hard links hard links symlink function directories making/removing removing directories mkdir function rmdir operator rmtree function chmod command (Unix) permissions changing chmod function (Unix) files ownership of, changing chown function user-ID, numeric ($uid) changing file ownership and group-ID ($gid) changing group membership and getpwnam function getgrnam function defined function utime function timestamps changing $atime (timestamp) changing $mtime (timestamp) changing $ctime (timestamp) changing modules basenames CPAN (Comprehensive Perl Archive Network) modules available from File\:\:Basename module basenames File\:\:Basename module for dirname function, File\:\:Basename module and modules using only some functions from import lists File\:\:Spec module files specifications of, File\:\:Spec module for manipulating methods classes -> little arrow little arrow (->) in method names portability modules and child processes, managing parent processes, managing processes managing system function date command (Unix) shell, avoiding exec function system function using vs. exec function environment variables variables environment PATH environment variable %ENV hash ` ` backquotes/backticks backquotes/backticks (` `) capturing output with output capturing using backquotes date command (Unix) capturing output and $now variable error messages standard output and list context using backquotes in who command (Unix) processes as filehandles filehandles processes as | pipe pipe (|) processes and find command (Unix) fork system call waitpid function perlipc manpage signals, sending/receiving Unix signals, sending/receiving SIGINT temporary files, cleaning up strings substrings index function strings finding substrings within first found occurrence of a substring, index function for last found occurrence of a substring, rindex function for rindex function substr operator index function using with substr operator sprintf function data formatting with sprintf function decimals rounding sprintf function and money, sprintf function for numbers sprintf function for while modifier sorting advanced sort subroutines (sort-definition subroutines) spaceship operator spaceship operator () Star Wars, spaceship operator and numbers spaceship operator for comparing three-way comparison operator (cmp) cmp (three-way comparison operator) comparison operators operators comparison reverse operator hash keys sorting sports scores, sorting databases DBM files DBM hashes AnyDBM_file manpage which_dbm utility utilities which_dbm dbmopen function tie interface dbmclose function each function DBM hashes and C programming language DBM files and NUL character DBM hashes and resources for further reading auxiliary lock files data manipulating with pack and unpack functions pack function format strings unpack function format letters perlfunc manpage format letters and whitespace in format strings fixed-length random-access databases databases fixed-length random-access open function databases files for, read/write access to seek function read function, database records and print function databases records and length function variable-length text databases databases variable-length text text databases files database, in-place editing of diamond operator () in-place editing of text files and date command (Unix) localtime function text databases and $^I variable backup files, text databases and ~ tilde tilde ("~"), as value for $^I variable files database, in-place editing of from command line command line, in-place editing from perlrun manpage, command-line options and -p command-line option -n command-line option -i.bak command-line option -w option -e command-line option Perl advanced techniques for eval block fatal errors trapping with eval block perldiag manpage errors and eval block caution with grep operator picking items from a list with % modulus operator modulus operator (%) used with grep operator grep operator vs. Unix's grep command "money numbers" decimals decimals formatting for output map operator grep operator vs. map operator hash keys omitting quotes from unquoted hash keys double quotes ("") omitting from hash keys barewords => big arrow big arrow (=>) arrows regular expressions regular expression engines quantifiers greedy/non-greedy resources for further reading regular expressions text matching multiple lines of anchors multiple-line text and /m option slices split operator undef operator slices and arrays slices and hashes slices and exercises in this book answers to answers to exercises in this book documentation for Perl Perl documentation for perltoc manpage perlfaq manpage perldoc manpage Friedl, Jeffrey resources for further reading regular expressions regular expressions resources for further reading regular expression engines resources for further information perlre manpage perlretut manpage perlrequick manpage namespaces, packages for packages Perl libraries and modules for libraries modules inside utility utilities inside CPAN (Comprehensive Perl Archive Network) inside utility available from CPAN (Comprehensive Perl Archive Network) modules available from CPAN (Comprehensive Perl Archive Network) libraries available from URLs CPAN perlmodinstall manpage use directives perlmod manpage writing modules and perlmodlib manpage writing modules and CGI module CGI_Lite module Cwd module cwd function current working directory working directory current, cwd function for determining Fatal module File\:\:Basename module basenames File\:\:Basename module for File\:\:Copy module files File\:\:Copy module for copying/moving filenames, File\:\:Spec module for manipulating files specifications of, File\:\:Spec module for manipulating File\:\:Spec module image files, Image\:\:Size module for files image, Image\:\:Size module for Image\:\:Size module email, Net\:\:SMTP module for SMTP servers, Net\:\:SMTP module for Net\:\:SMTP module POSIX module Sys\:\:Hostname module hostname function Text\:\:Wrap module text Text\:\:Wrap module for wrap function word-wrapping, Text\:\:Wrap module for Time\:\:Local module timelocal function pragmas perlmodlib manpage pragmas and use directives pragmas and constant pragma diagnostics pragma lib pragma modules lib pragma for use strict pragma strict pragma vars pragma warnings pragma -w option vs. warnings pragma databases system databases Windows Registry Registry (Windows) Unix password databases password databases (Unix) domain-name databases flat-file databases relational databases DBI module databases DBI module and perlop manpage operators and operators perlop manpage and perlfunc manpage operators and operators perlfunc manpage and tr/// operator characters transliterating/counting with tr/// operator here documents multiline string quoting quoting multiline string perldata manpage, here documents and mathematics mathematical functions square root cosine logarithm absolute value builtin functions mathematical functions and perlfunc manpage mathematical functions and POSIX module math functions and numbers complex/imaginary and complex numbers imaginary numbers Math\:\:Complex module numbers high-precision/large large numbers high-precision numbers Math\:\:BigInt module Math\:\:BigFloat module lists arrays map operator perlfunc manpage and perlfunc manpage map operator and grep operator perlfunc manpage and perlfunc manpage grep operator and splice operator arrays splice operator for perlfunc manpage splice operator and bitstrings vec operator for vec operator perlfunc manpage vec operator and formats reports, formats for perlform manpage, formats and networking IPC System V IPC interprocess communication perlfunc manpage System V IPC and perlipc module, System V IPC and TCP/IP sockets sockets (TCP/IP) Web socket-support and LWP module security Perl security and data-flow analysis taint checking perlsec manpage debugger for Perl perldebug manpage B\:\:Lint module Web CGI programs and CGI module CGI_Lite module security CGI programs and Perl security and resources for further reading Perl using with the Web command-line options perlrun manpage, command-line options and builtin variables perlvar manpage, builtin variables and continue block BEGIN block syntax extensions perlsyn manpage syntax extensions and perlmod manpage syntax extensions and references pointers (C programming language) perlreftut manpage, references and perlref manpage, references and complex data structures data structures, complex perldsc manpage, data structures and perllol manpage, data structures and object-oriented (OO) programming OO (object-oriented) programming perlobj manpage, object-oriented programming and perlboot manpage, object-oriented programming and resources for further reading Perl object-oriented programming and subroutines anonymous anonymous subroutines closures DBM hashes DBM files tied variables variables tied perltie manpage, tied variables and overload module operators overload module for dynamic loading code dynamic loading and binary extensions, dynamic loading and embedding code code embedding licenses for Perl embedding code snippets and mod_perl software programming languages converting to Perl Perl converting other programming languages to conversion programs s2p conversion program a2p conversion program find command (Unix) find2perl command -eval option, find2perl command and temporary files, cleaning up command-line options modules for Getopt\:\:Long module Getopt\:\:Std module pod format plain-old documentation format documentation for Perl embedding perlpod manpage perlopentut manpage, filehandles and locales Unicode perllocale manpage threads fork system call using instead of threads perlfork manpage perlthrtut manpage Tk module set GUIs (graphical user interfaces) graphical user interfaces (GUIs) resources for further reading Tk modules