Perl reference
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Reference for various things in Perl. See also Perl built-in functions.
Escape Sequences
\a | bell (ctrl-G, 007 decimal) |
\b | backspace (ctrl-H, 008 decimal) |
\cn | ctrl-n (e.g. \cj = CTRL-J, i.e. Line Feed) |
\e | ESC (027 decimal, 033 octal) |
\f | FF |
\l | converts next letter to lowercase |
\n | newline - system-dependent (CRLF on DOS/Win) |
\r | CR (013 decimal) |
\t | TAB (ctrl-I, 009 decimal) |
\u | converts next letter to uppercase |
\L | converts all characters to lowercase, from here to next \E |
\U | converts all characters to uppercase, from here to next \E |
\E | ends case conversion started by \L or \U |
\' | prints a literal single-quote |
\" | prints a literal double-quote |
\$ | prints a literal dollar sign |
\\ | prints a literal backslash (not doubled) |
\0nnn | prints the ASCII character numbered nnn in octal |
\xnn | prints the ASCII character numbered nn in hexadecimal |
Operators
Arithmetic
+ | add | $x+$y |
- | subtract | $x-$y |
* | multiply | $x*$y |
/ | divide | $x/$y |
% | modulo (remainder) | $x%$y -> remainder of x/y |
** | exponent | $x**$y -> xy |
++ | incrememt | $x++ or ++$x -> x is incremented by 1 |
-- | decrement | $x-- or --$x -> x is decremented by 1 |
Comparisons | ||
== | is equal | $x==$y returns true iff x equals y |
!= | is different | $x!=$y returns true iff x does not equal y |
< | is less than | $x<$y returns true iff x is smaller than y |
> | is more than | $x>$y returns true iff x is larger than y |
Strings | ||
. | concatenate | $x.$y combines the strings in x and y |
eq | strings are equal | $xeq$y returns true iff the two strings are identical |
ne | strings are different | $xne$y returns true iff the two strings are different |
Other | ||
?: | conditional result | $a?$b:$c returns $b if $a is true, otherwise returns $c |
File Test Operators
All operators are used like this:
-x $filename
-r | Is the file readable? |
-w | Is the file writable? |
-x | Is the file executable? |
-e | Does the file exist? |
-z | Is the file empty? (i.e. zero bytes) |
-s | File length in bytes |
-f | Is the file an ordinary file? |
-d | Is the file a directory? |
-l | Is the file a symbolic link? (UNIX/Linux only) |
-p | Is file a named pipe? |
-S | Is the file a socket? |
-T | Is the file a text file? |
-B | Is the file a binary file? (!-T) |
-M | Number of days since file was last modified |
-A | Number of days since file was last accessed |
Special Variables
@ARGV | array of command-line arguments with which Perl was invoked |
%ENV | hash of all environment variables (see http://vbz.net/cgi-bin/env for a sample listing) |
$0 | name of Perl program file (the outermost one; may or may not include path, depending on system (in Linux, it does not)) |
$^A | current value of the accumulator used by the write() function |
$^D | current value of Perl's debugging flags |
$^F | maximum system file descriptor (typically 2) not sure what this means |
$^L | what characters are printed to accomplish a form feed |
$^T | time at which the script began running, in seconds since 00:00:00 GMT January 1, 1970 |
$^W | is true if warnings have been turned on (by running Perl with the -w command option) |
$^X | filespec of the Perl interpreter |
$_ | The default input and pattern-searching space; default argument for many functions. |
@_ | list of arguments passed to subroutine (usually in parentheses) |
$) | effective group ID of the current process (UNIX/Linux) |
$( | real group ID of the current process (UNIX/Linux) |
$] | version number of the Perl interpreter |
$[ | The index of the first element in an array, and of the first character in a substring. |
$< | |
$> | effective user ID of the current process (UNIX/Linux) |
$/ | string to be used as input record separator; default = newline |
$\ | string to be used as output record separator in print() |
$: | "soft-hyphen" characters, i.e. the set of characters after which a line may be broken to fill continuation fields (starting with ^) in a format. Default is space, newline, hyphen. |
$; | The subscript separator for multi-dimensional array emulation. |
$. | The current input line number (or record number) of the last filehandle that was read. |
$, | output field separator for print() function, i.e. the separator for printing arrays |
$" | This is similar to "$," except that it applies to array values interpolated into a double-quoted string (or similar interpreted string) |
$# | The output format for numbers display via print() |
$$ | The process number of the Perl running this script |
$? | The status returned by the last child process, i.e. pipe close, backtick(``) command or system operator. |
$! | If used in a numeric context, yields the current value of errno, with all the usual caveats. (This means that you shouldn't depend on the value of $! to be anything in particular unless you've gotten a specific error return indicating a system error.) If used in a string context, yields the corresponding sysem error string. |
$@ | The Perl syntax error or routine error message from the last eval, do-FILE, or require command. If set, either the compilation failed, or the die function was executed within the code of the eval. |
Output Flags | |
If set to nonzero, forces a flush after every write or print | |
$* | If set to zero, pattern-matching assumes that strings contain a single line (for optimization purposes). Default = 0 |
ReportingThese refer to the currently selected filehandle; each filehandle maintains its own set of variables. | |
$% | Current page number |
$= | Current page length |
$- | Number of lines remaining on the page |
$~ | Name of the current report format (default is the filenandle's name) |
$^ | Name of the current top-of-page format (default is the filehandle's name plus "_TOP") |
Pattern Matching (regex)These are associated with the last successful pattern match. | |
$n | in the replacement section, indicate that the nth matched section in parentheses should be used here (first matched parentheses becomes $1, second becomes $2, etc., up through $9) |
$& | Contains the string matched by the last pattern match. Introduces CPU/memory overhead for all regex operations in the script; avoid. |
$` | The string preceding whatever was matched by the last pattern match, not counting patterns matched in nested blocks that have been exited already. Introduces CPU/memory overhead for all regex operations in the script; avoid. |
$' | The string following whatever was matched by the last pattern match, not counting patterns matched in nested blockes that have been exited already. Introduces CPU/memory overhead for all regex operations in the script; avoid. |
$+ | The last bracket matched by the last search pattern. This is useful if you don't know which of a set of alternative patterns matched. |
$* | When set to 1, string searching is done for multiple lines within the string (i.e. if the string contains newline characters); otherwise, presumably the search stops at the first newline. |
Portions of this were shamelessly copied from here, at least until more information can be found. Other portions were copied from Discover Perl 5 by Naba Barkakati, ISBN 0-7645-3076-3