Data Types

Type	Identifier	Description	Example
scalar	$name	a single value (string, numeric, etc.)	$name=4.6; $name2= "a_string";
list	()	ordered scalar data	@x= (1,2,"three",4.0); @letters= (A..B); @numbers=(0..9);
array	@name	a variable that holds a list	@name=(1,"two",3.14,$something); $listlength= @name; #result is 4 (scalar context)
hash	%name	a set of keys and elements	$name{key} = value; $fred_list= %fred; %smooth= ("aaa","bbb","123.4",567.8); slice: @score{"fred","barney","dino"}= (21,47,6); @league{keys %team1}=values %team1;

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Operators

symbol	example(s)	action
=	$a=$b; $a=4;	assignment
=~	$a=~/regex/	performs regular expression match, substitute
. or .=	$str = $str . "b"; $str.="b"; #same thing	string concatenate

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Pragmas

prqagma	meaning
use strict;	generate error if varialbes not declared with my()

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Perl Functions

Name	Argument(s) Type	Result Type	Action
qw	comma-separated strings	list	double-quotes arguments
push	list,scalar		appends 'scalar' to 'list'
pop
shift
unshift
reverse	list	list	reverses order of list elements
sort	list	list	places elements in ascending ascii order
chomp	array or scalar variable		removes last record separator from the scalar or from each element of the array
<STDIN>	n/a	scalar or array, depending on context	as scalar: returns next line of standard input, including newline. as array: returns all lines of input to EOF.
<> (diamond)		"	as <STDIN> but refers to files listed in @argv
rand	scalar	scalar	returns a random number between zero and (argument-1)
srand	none	none	initializes the random number generator.
keys	hash	list	returns list consisting of keys in the hash. arbitrary order!
values	hash	list	returns list containing values in the hash. same arbitrary order
each	hash	2 element list	returns the next successive key/value pair in the hash
delete	hash element	n/a	removes the referenced element from the hash. example: delete $hashname{"a_key"};
defined	anything	logical	returns FALSE if argument is undef. (usually redundant?)
split	regex,string	list	Returns list consisting of parts of string  delimited by regex. Default regex is /\s+/ and default string  is $_.
join	string,list	string	makes a big string of the elements in list , separated by string Example: $bigstring= join($glue,@list);
die "message\n";			terminate and print 'message' to STDERR. System error message appended unless \n included.
warn "message";			as 'die' but don't terminate.

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Subroutines

sub name { my(list of local variables ); (par1, par2, par3...) = @_; #copies of argument list parn= $_[$#_]; #last argument # or 'my(par1,par2,par3)=@_;' expressions; return value; }
my(list of variables );	variables entirely private to subroutine
local(list of variables );	variables local to subroutine and decendants

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Special Variables

Symbol	Meaning/Use	Example
$_	Default variable	default i/o target, foreach parameter, match string,...
@_	Subroutine argument list	reference arguments as $_[n] within the subroutine

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I/O

open(HANDLE,">filename");	Opens a file for reading. Prefix '>' or '>>' opens to write.
close(HANDLE);	Closes file (happens automatically if re-opened or at termination of program)
die "message\n"; warn "mess";	output to STDERR. 'die' terminates program. system message if no '\n'
<STDIN>, <STDOUT>	default filehandles for IO
print [FILEHANDLE] item1,item2,...	write to FILEHANDLE
File Tests $readable= -r $filename; $age= -M "/usr/bin/perl";	-r File or directory is readable -w File or directory iw writeable -x File or directory is executable -o File or directory is owned by user -R File or directory is readable by real user, not effective user -W File or directory is writable by real user, not effective user -X File or directory is executable by real user, not effective user -O File or directory is owned by real user, not effective user -e File or directory exists -z File exists and has zero size (directories are never empty) -s File or directory exists and has nonzero size (the returned value is the size in bytes) -f Entry is a plain file -d Entry is a directory -l Entry is a symlink -S Entry is a socket -p Entry is a named pipe (a 'fifo') -b Entry is a block-special file (like a mountable disk) -c Entry is a character-special file (like an I/O device) -u File or directory is setuid -g File or directory is setgid -k File or directory has the sticky bit set -t isatty() on the filehandle is true -T File is "text" -B File is "binary" -M Modification age in days -A Access age in days -C Inode-modification age in days

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Flow Control

Statement	Format	Comment
if / unless elsif else	if (test) { statement_block; } elsif (test) { statement_block; } else { statement_block; } #or exp1  if exp2; exp1 unless exp2;	Note it's spelled elsif, not elseif!
while/until	until (test) { statement_block; } #or exp1 while exp2; exp1 until exp2;
do {} while do {} until	do { statement block; } until expression;
for	for (initial_exp; test_exp; re-init_exp) { statement_block; }
foreach	foreach $i (@some_list) { statement_block; }	$i may be omitted in which case $_ is assumed.
last [LABEL]	last;	breaks out of the innermost enclosing loop block, or out of the block LABEL .
next [LABEL]	next;	skips remainder of innermost enclosing loop block without exiting the loop. If LABEL is present go to the beginning of the block LABEL.
redo	redo;	jumps to beginning of the current loop block

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Regular Expressions

a	a single character - matches only itself
. (dot)	matches any single character except newline
/[aeiou]/, /[A-Z]/	character class. Matches any single mentioned character.
\n	matches newline
\000-\377	octal representation
/[^0-9]/	negated character class
\d \w \s	a digit, word-character, or space-character
\D \W \S	NOT a digit, word, or space character
* or {0,}	zero or more of the preceeding character
+ or {1,}	one or more of the preceeding character
? or {0,1}	zero or one of the preceeding character
/a{m,n}/	"m" to "n" a's.
/a{m}/	exactly "m" a's
/a{m,}/	"m" or more a's
/a(.)b(*)c\2d\1/	items matched by parenthesized patterns may be used later in the pattern by '\n' where 'n' refers to the nth parenthesized pattern match. '$n' is a scalar containing the matched string which can be used elsewhere in the script after the pattern match. Use (?:pattern ) to prevent the memory function.
Precedence	Parentheses ( )  (?:) Multipliers ? + * {m,n} ?? +? *? {m,n}? Sequence & Anchoring abc ^ $ \A \Z (?= )  (?! ) Alternation |
a|b	match pattern 'a' or 'b'
\b (\B)	anchors to a word boundary (NOT a word boundary)
^a	requires 'a' as first character in string
a$	requires 'a' as last character in string
\A \Z (?=...) (?!...)	anchors -- not yet described
$a =~ regular exp	matches against $a (instead of $_)
m#pattern#	'm' indicates use '#' (or whatever follows) as delimeter instead of '/'.
$` / $& / $'	read-only variables containing the part of the string before/in/following the match
s/old/new/g	substitute 'new' for 'old'. If 'g' is present, do substitution everywhere.
suffices	g perform substitution repeatedly i ignore case
\u, \U, (\l, \L)	uppercase (lowercase) the following letter or STRING.