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Perl Reference Card

1.3 Hashes

4 System Interaction

%h=(k1 => “val1”,k2 => 3);

hash initialization

system(“cat $f|sort -u>$f.s”); system call

This is version 2 of the perl reference card.

$val = $map{k1};

recall value

(cl) 2008 Michael Goerz <goerz@physik.fu-berlin.de>.

@a = readpipe(“lsmod”);

catch output

@a = %h;

array of keys and values

$today = “Today: “.`date`;

catch output

Information taken liberally from the perl documentation and various other sources.

%h = @a;

create hash from array

chroot(“/home/user/”);

change root

You may freely distribute this document.

foreach $k (keys(%h)){..}

iterate over list of keys

while (<*.c>) {}

operate on all c-files

foreach $v (vals(%h)){..}

iterate over list of values

unlink(“/tmp/file”);

delete file

while (($k,$v)=each %h){..} iterate over key-value-pairs

if (-f “file.txt”){...}

file test

1 Variable Types

delete $h{k1};

delete key

File Tests:

exists $h{k1}

does key exist?

-r, -w

readable, writeable

defined $h{k1}

is key defined?

1.1 Scalars and Strings

-x

executable

-e

exists

chomp($str);

discard trailing \n

-f, -d, -l

is file, directory, symlink

$v = chop($str);

$v becomes trailing char

-T, -B

text file, binary file

eq, ne, lt, gt, le, ge, cmp

string comparison

2 Basic Syntax

-M, -A

mod/access age in days

$str = “0” x 4;

$str is now “0000”

@stats = stat(“filename”);

13-element list with status

($a, $b) = shift(@ARGV);

read command line params

$v = index($str, $x);

find index of $x in $str,

More: chmod, chown, chroot, fcntl, glob, ioctl, link,

sub p{my $var = shift; ...} define subroutine

$v = rindex($str, $x);

starting from left or right

lstat, mkdir, opendir, readlink, rename, rmdir,

p(“bla”);

execute subroutine

$v = substr($str, $strt, $len);

extract substring

symlink, umask, utime

if(expr){} elsif {} else {} conditional

$cnt = $sky =~ tr/0-9//;

count the digits in $sky

unless (expr){}

negative conditional

$str =~ tr/a-zA-Z/ /cs;

change non-alphas to space

while (expr){}

while-loop

$v = sprintf(“%10s %08d”,$s,$n); format string

until (expr){}

until-loop

Format String: %[flags][0][width][.precision][mod]type

5 Input/Output

do {} until (expr)

postcheck until-loop

types:

for($i=1; $i<=10; $i++){}

for-loop

character

open(INFILE,"in.txt") or die;

open file for input

foreach $i (@list){}

foreach-loop

d(i)

signed decimal int

open(INFILE,"<:utf8","file");

open file with encoding

last, next, redo

end loop, skip to next, jump to top

e(E)

scientific notation

open(TMP, "+>", undef);

open anonymous temp file

eval {$a=$a/$b; };

exception handling

decimal floating point

open(MEMORY,'>', \$var);

open in-memory-file

warn $@ if $@;

g, G

shorter %e or %f / %E or %f

open(OUT,">out.txt") or die;

open output file

signed octal

open(LOG,">>my.log") or die;

open file for append

string of chars

open(PRC,"caesar <$file |");

read from process

u, x, X

unsigned decimal int / hex int / hex int in caps

open(EXTRACT, "|sort >Tmp$$"); write to process

3 References and Data Structures

address pointer

$line

= <INFILE>;

get next line

nothing printed

@lines

= <INFILE>;

slurp infile

$aref = \@a;

reference to array

modifiers: h,l,L

arg is short int / long int, double/ long double

foreach $line (<STDIN>){...}

loop of lines from STDIN

$aref = [1,"foo",undef,13]; anonymous array

More: chr, crypt, hex, lc, lcfirst, length, oct, ord,

print STDERR "Warning 1.\n";

print to STDERR

$el = $aref->[0];

access element of array

pack, q/STRING/, qq/STRING/, reverse, uc, ucfirst

$el = @{$aref}[0];

close INFILE;

close filehandle

$aref2 = [@{$aref1}];

copy array

More: binmode, dbmopen, dbmclose, fileno, flock,

$href = \%h;

reference to hash

format, getc, read, readdir, readline, rewinddir,

1.2 Arrays and Lists

$href ={APR => 4,AUG => 8}; anonymous hash

seek, seekdir, select, syscall, sysreed, sysseek,

@a = (1..5);

array initialization

$el = $href->{APR};

access element of hash

tell, telldir,truncate, pack, unpack, vec

$i = @a;

number of elements in @a

$el = %{$href}{APR};

($a, $b) = ($b, $a);

swap $a and $b

$href2 = {%{$href1}};

copy hash

$x = $a[1];

access to index 1

if (ref($r) eq "HASH") {}

checks if $r points to hash

$i = $#a;

last index in @a

6 Regular Expressions

@a = ([1, 2],[3, 4]);

2-dim array

push(@a, $s);

appends $s to @a

($var =~ /re/), ($var !~ /re/) matches / does not match

$i = $a[0][1];

access 2-dim array

$a = pop(@a);

removes last element

m/pattern/igmsoxc

matching pattern

%HoA=(fs=>["f","b"],

hash of arrays

chop(@a);

remove last char (per el.)

sp=>["h","m"]);

qr/pattern/imsox

store regex in variable

$a = shift(@a);

removes first element

$name = $HoA{sp}[1];

access to hash of arrays

s/pattern/replacement/igmsoxe

search and replace

reverse(@a);

reverse @a

$fh = \*STDIN

globref

Modifiers:

@a = sort{$ela <=> $elb}(@a);

sort numerically

$coderef = \&fnc;

code ref (e.g. callback)

case-insensitive

compile once

@a = split(/-/,$s);

split string into @a

$coderef =sub{print "bla"}; anon subroutine

global

extended

$s = join(“, ” @c);

join @a elements into string

&$coderef();

calling anon subroutine

multiline

don't reset pos (with g)

@a2 = @a[1,2,6..9];

array slice

sub createcnt{ my $c=shift;

closure, $c persists

as single line (. matches \n)

evaluate replacement

@a2 = grep(!/^#/, @a);

remove comments from @a

return sub {

print "$c++"; }; }

*foo{THING}

foo-syntax for creating refs

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