10stripe's Perl Cheat-Sheet

As a companion to our earlier regular expression cheat-sheet, we have put together a general cheat-sheet for various parts of the Perl programming language. Perl is a big, big language, so of course we couldn't cover the entire language. But we did condense down some of the most frequently needed, hardest to memorize parts.

This is not a comprehensive overview of Perl and it will not teach you all of Perl. If you are completely new to Perl, we would suggest using this as a supplement to Learning Perl by Schwartz et al (buying from Amazon helps support 10stripe).

If you would like a print version, we strongly recommend the PDF version of this page. We have made some adjustments so that printing this HTML document should also be a workable solution (results will look best in a modern browser with strong CSS support). It won't be quite as nice as the PDF version.

Bitwise Operators

& And

| Or

^ XOR

<< Shift left (Usage: 6 << 2 shifts left 2)

>> Shift right

~ Bitwise negation

File Tests

Usage: if (-r $filename) {}

-r Readable by this (effective) user/group

-w Writable by this (effective) user/group

-x Executable by this (effective) user/group

-o Owned by this (effective) user/group

-R Readable by this real user/group

-W Writable by this real user/group

-X Executable by this real user/group

-O Owned by this real user/group

-e Exists

-z Exists and has zero size (false for directories)

-s Exists and nonzero size (returns size in bytes)

-f Is a plain file

-d Is a directory

-l Is a symbolic link

-S Is a socket

-p Is a named pipe ("fifo")

-b Is a block-special file (like a mountable disk)

-c Is a character-special file (like an I/O device)

-u Is a setuid

-g Is a setgid

-k Has sticky bit set

-t Is a tty

-T "Looks like" plain text (reads beginning of file)

-B "Looks like" binary file (reads beginning of file)

-M Time since last modified (floating-point days)

-A Time since last accessed (floating-point days)

-C Time since inode last modified (floating-point days)

printf and sprintf Formats

%c Character with the given number

%s String

%d Signed integer, in decimal

%u Unsigned integer, in decimal

%o Unsigned integer, in octal

%x Unsigned integer, in hexadecimal

%e Floating-point number, in scientific notation

%f Floating-point number, in fixed decimal notation

%g Floating-point number, in %e or %f notation (auto)

%% Literal percent sign

Variable Types and Sigils

$scalar Single value

@array List of values

%hash List of key/value pairs

*typeglob All types (holds $typeglob, @typeglob, etc.)

&subroutine Named block of instructions

\$reference Memory address (or \@reference, etc)

Flow Control

{} "Naked" block for scope control

while (true) {} Loop while evaluates to true

until (false) {} Equivalent to while !(false) {}

if (true) {} Execute once if evaluates to true

elsif (true) {} Follows if, note the missing ‘e’

else {} Follows if

unless (false) {} Equivalent to if !(false) {}

for (initial;test;iterate) {} Loop, e.g. for ($i=0;$i<9;$i++) {}

foreach (@items) {} Option: foreach $item (@items) {}

last Exit loop; like C’s break

next Advance loop to next iteration

redo Repeat loop, do not iterate

pack and unpack Templates

a Null-padded string of bytes

A Space-padded string of bytes

b Bit string, ascending bit order inside each byte (like vec)

B Bit string, descending bit order inside each byte

c Signed char (8-bit integer)

C Unsigned char (8-bit integer); see U for Unicode

d Double-precision (64-bit) floating point, native format

f Single-precision (32-bit) floating-point, native format

h Hexadecimal string, low nybble first

H Hexidecimal string, high nybble first

i Signed integer, native format

I Unsigned integer, native format

l Signed long, always 32 bits

n 16-bit short in "network" (big-endian) order

N 32-bit long in "network" (big-endian) order

p Pointer to a null-terminated string

P Pointer to a fixed-length string

q Signed quad (64-bit integer) value

Q Unsigned quad (64-bit integer) value

s Signed short value, always 16 bits

S Unsigned short value, always 16 bits

u A uuencoded string

U Unicode character number

v 16-bit short in "VAX" (little-endian) order

V 32-bit long in "VAX" (little-endian) order

w BER compressed integer

x Null byte (skip forward a byte)

X Back up a byte

Z Null-terminated (and null-padded) string of bytes

@ Null-fill to absolute position