Perl Functions References

Perl - Core Functions Reference

This section provides a reference to important built-in functions in Perl. Modern Perl development often leverages comprehensive modules from CPAN for specialized tasks, but understanding these core functions is fundamental.

Note: For many traditional functions (e.g., low-level socket operations, DBM access), dedicated CPAN modules often provide more robust and feature-rich alternatives. Always check CPAN for modern best practices for specific problem domains.

Below is a list of significant functions supported by Perl. Descriptions have been updated for clarity and modern context.

• abs - Returns the absolute value of its argument.
• accept - Accepts an incoming socket connection. See also IO::Socket or Mojo::IOLoop for higher-level networking.
• alarm - Schedules a SIGALRM signal. Useful for timeouts, but consider modules like Sys::SigAction for robust signal handling.
• atan2 - Arctangent of Y/X in the range -PI to PI.
• bind - Binds an address to a socket. See also IO::Socket.
• binmode - Prepares a filehandle for binary I/O, crucial on systems like Windows.
• bless - Turns a reference into an object by associating it with a class name.
• caller - Returns the context of the current subroutine call, useful for debugging and creating call stacks.
• chdir - Changes the current working directory.
• chmod - Changes the permissions on a list of files.
• chomp - Removes a trailing newline (or record separator as defined by $/) from a string.
• chop - Removes the last character from a string (generally, chomp is preferred).
• chown - Changes the ownership (user and group) on a list of files.
• chr - Returns the character represented by a number in the character set.
• chroot - Makes a directory the new root for path lookups (requires superuser privileges).
• close - Closes a filehandle, pipe, or socket.
• closedir - Closes a directory handle opened by opendir.
• connect - Connects to a remote socket. See also IO::Socket.
• continue - Defines an optional trailing block in a while or foreach loop, executed before the condition is re-evaluated.
• cos - Returns the cosine of an angle (in radians).
• crypt - One-way encryption, typically for password hashing. Modern applications should use modules like Authen::Passphrase for stronger hashing algorithms.
• dbmclose - Closes a DBM file. Largely superseded by modules like DB_File or BerkeleyDB.
• dbmopen - Opens a DBM file. Largely superseded by modules like DB_File or BerkeleyDB.
• defined - Tests whether a value, variable, or function is defined (not undef).
• delete - Deletes a key-value pair from a hash, or an element from an array slice.
• die - Raises an exception or terminates the program with an error message.
• do - Executes a block or a file. do FILE is similar to require but doesn’t do error checking or import symbols.
• dump - Creates an immediate core dump (rarely used, platform-dependent).
• each - Iterates over a hash, returning key-value pairs. Note: iteration order is not guaranteed. Consider keys and a loop for predictable order.
• endgrent - Cleans up after processing group file entries.
• endhostent - Cleans up after processing hosts file entries.
• endnetent - Cleans up after processing networks file entries.
• endprotoent - Cleans up after processing protocols file entries.
• endpwent - Cleans up after processing passwd file entries.
• endservent - Cleans up after processing services file entries.
• eof - Tests if the end of a filehandle has been reached.
• eval - Executes a string as Perl code (eval STRING) or traps exceptions from a block (eval BLOCK). Essential for error handling.
• exec - Replaces the current program with another program.
• exists - Tests whether a hash key exists (even if its value is undef).
• exit - Terminates the program with a specified exit status.
• exp - Returns e (Euler’s number) raised to a power.
• fcntl - Provides file control system calls (low-level).
• fileno - Returns the file descriptor for a filehandle.
• flock - Applies or removes an advisory lock on an open file.
• fork - Creates a child process (on Unix-like systems).
• format - Declares a picture format for use with write(). Rarely used in modern Perl; see templating engines like Template Toolkit.
• formline - Internal function used by format (rarely called directly).
• getc - Gets the next character from a filehandle.
• getgrent - Gets the next group record from the group file.
• getgrgid - Gets a group record by group ID (GID).
• getgrnam - Gets a group record by group name.
• gethostbyaddr - Gets a host record by its network address.
• gethostbyname - Gets a host record by its name.
• gethostent - Gets the next hosts record.
• getlogin - Returns the current login name.
• getnetbyaddr - Gets a network record by its address.
• getnetbyname - Gets a network record by its name.
• getnetent - Gets the next networks record.
• getpeername - Gets the socket address of the other end of a socket connection.
• getpgrp - Gets the process group ID.
• getppid - Gets the parent process ID.
• getpriority - Gets the current process priority (nice value).
• getprotobyname - Gets a protocol record by name.
• getprotobynumber - Gets a protocol record by number.
• getprotoent - Gets the next protocols record.
• getpwent - Gets the next passwd record.
• getpwnam - Gets a passwd record by username.
• getpwuid - Gets a passwd record by user ID (UID).
• getservbyname - Gets a services record by name.
• getservbyport - Gets a services record by port number.
• getservent - Gets the next services record.
• getsockname - Gets the socket address for a given socket.
• getsockopt - Gets socket options.
• glob - Expands a pattern into a list of filenames (filename globbing).
• gmtime - Converts a Unix timestamp into a list of time components (year, month, day, etc.) for GMT/UTC.
• goto - Transfers control to a labeled statement. Its use is strongly discouraged in modern programming.
• grep - Filters elements from a list for which a given code block or expression evaluates to true.
• hex - Converts a hexadecimal string to a decimal number.
• import - Imports symbols from a module into the current package’s namespace.
• index - Finds the position of the first occurrence of a substring within a string.
• int - Returns the integer portion of a number (truncates towards zero).
• ioctl - Performs I/O control system calls (low-level, system-dependent).
• join - Joins elements of a list into a single string using a separator.
• keys - Returns a list of all keys from a hash.
• kill - Sends a signal to a list of processes.
• last - Exits the innermost loop prematurely (similar to break in other languages).
• lc - Returns a lowercased version of a string.
• lcfirst - Returns a string with its first character lowercased.
• length - Returns the length (in bytes by default, characters if use utf8 or use feature 'unicode_strings' is in effect for strings with Unicode properties) of a string.
• link - Creates a hard link between two filenames.
• listen - Listens for incoming connections on a socket. See also IO::Socket.
• local - Creates a temporary, dynamically scoped value for a global (package) variable. my is generally preferred for lexical scoping.
• localtime - Converts a Unix timestamp into a list of time components for the local timezone.
• lock - Gets a thread lock on a variable, subroutine, or method (used with threads and threads::shared).
• log - Returns the natural logarithm (base e) of a number.
• lstat - Like stat, but stats a symbolic link itself rather than the file it points to.
• m// - The match operator, used for regular expression matching. Can also be written as //.
• map - Transforms a list by applying a code block or expression to each element.
• mkdir - Creates a directory.
• msgctl, msgget, msgrcv, msgsnd - System V IPC message queue functions. Low-level; consider higher-level IPC mechanisms like sockets or message queuing systems (e.g., Redis, RabbitMQ) via CPAN modules.
• my - Declares lexically scoped variables. This is the standard way to declare variables in modern Perl.
• next - Skips to the next iteration of the current loop (similar to continue in other languages).
• no - Unimports symbols or disables pragmas at compile time (e.g., no strict).
• oct - Converts an octal string (or hex if prefixed with 0x) to a decimal number.
• open - Opens a file, pipe, or process for I/O. Modern Perl often uses the three-argument form with lexical filehandles (e.g., open my $fh, '<', $filename).
• opendir - Opens a directory for reading with readdir.
• ord - Returns the numeric value (ordinal) of the first character in a string.
• our - Declares package variables that are lexically scoped but accessible via their fully qualified name.
• pack - Converts a list of values into a binary string representation according to a template.
• package - Declares a namespace (package).
• pipe - Creates a pair of connected filehandles (an inter-process communication channel).
• pop - Removes and returns the last element from an array.
• pos - Finds or sets the current match offset for a string when using m//g.
• print - Outputs a list of strings to a filehandle (STDOUT by default).
• printf - Outputs a formatted string to a filehandle.
• prototype - Returns the prototype of a subroutine (rarely needed by application programmers).
• push - Appends one or more elements to the end of an array.
• q// - Single-quotes a string, performing minimal interpolation.
• qq// - Double-quotes a string, performing interpolation of variables and escape sequences.
• qr// - Compiles a regular expression, returning a regex object.
• quotemeta - Quotes (escapes) all non-alphanumeric characters in a string for safe use in a regex.
• qw// - Quote Words: splits a string by whitespace into a list of words, treating each as single-quoted.
• qx// - Executes a command in a subshell and returns its standard output (same as backticks “).
• rand - Returns a pseudorandom floating-point number between 0 and its argument (or 1 if no argument).
• read - Reads a specified number of bytes from a filehandle into a buffer.
• readdir - Reads directory entries from a directory handle opened by opendir.
• readline - Reads a line from a filehandle (often used implicitly with the <FILEHANDLE> operator).
• readlink - Returns the value of a symbolic link.
• readpipe - Executes a system command and returns its standard output (same as qx// or backticks).
• recv - Receives a message over a socket.
• redo - Restarts the current loop iteration without re-evaluating the condition or executing continue block.
• ref - Returns the type of the referenced value (e.g., ‘ARRAY’, ‘HASH’, ‘SCALAR’, or the class name for a blessed reference).
• rename - Renames a file.
• require - Loads a module or file at runtime if not already loaded. Ensures code is compiled only once.
• reset - Resets variables in the current package (rarely used).
• return - Exits a subroutine, optionally returning a value.
• reverse - Reverses the order of elements in a list, or the characters in a string (in list or scalar context, respectively).
• rewinddir - Resets the current position of a directory handle opened by opendir to the beginning.
• rindex - Finds the position of the last occurrence of a substring within a string.
• rmdir - Removes an empty directory.
• s/// - The substitution operator, for regex search and replace.
• scalar - Forces an expression to be evaluated in scalar context.
• seek - Repositions the file pointer for a filehandle (for random access I/O).
• seekdir - Repositions a directory handle opened by opendir.
• select - Sets the default filehandle for output, or performs I/O multiplexing (with a bitmask of filehandles).
• semctl, semget, semop - System V semaphore functions. Low-level; see IPC::SysV or consider higher-level synchronization primitives.
• send - Sends a message over a socket.
• setgrent, sethostent, setnetent, setprotoent, setpwent, setservent - Prepare for iterating through system database files (group, hosts, etc.).
• setpgrp - Sets the process group of a process.
• setpriority - Sets a process’s priority (nice value).
• setsockopt - Sets socket options.
• shift - Removes and returns the first element from an array, or from @_ within a subroutine if no array is specified.
• shmctl, shmget, shmread, shmwrite - System V shared memory functions. Low-level; see IPC::SysV or IPC::Shareable.
• shutdown - Disables reads, writes, or both on a socket connection.
• sin - Returns the sine of an angle (in radians).
• sleep - Pauses execution for a specified number of seconds.
• socket - Creates a socket. See also IO::Socket.
• socketpair - Creates a pair of connected (unnamed) sockets.
• sort - Sorts a list of values. Can take a custom comparison subroutine or block.
• splice - Adds or removes elements from an array at a specified offset.
• split - Splits a string into a list of substrings based on a regex delimiter.
• sprintf - Returns a formatted string (similar to printf but returns the string instead of printing it).
• sqrt - Returns the square root of a number.
• srand - Seeds the pseudorandom number generator (rand). Automatic seeding usually makes explicit calls unnecessary.
• stat - Returns status information for a file (mode, size, timestamps, etc.).
• study - Analyzes a string to optimize subsequent regex matches on it. Rarely beneficial on modern Perl due to regex engine improvements.
• sub - Declares a subroutine (function), possibly anonymously.
• substr - Extracts or replaces a portion of a string.
• symlink - Creates a symbolic link to a file.
• syscall - Executes an arbitrary system call (very low-level, platform-dependent).
• sysopen - Opens a filehandle using system-level open flags.
• sysread - Reads from a filehandle without using Perl’s I/O buffering.
• sysseek - Repositions the I/O pointer for a filehandle used with sysread and syswrite.
• system - Executes a system command. Returns the exit status of the command.
• syswrite - Writes to a filehandle without using Perl’s I/O buffering.
• tell - Returns the current position (offset) of a filehandle.
• telldir - Returns the current position of a directory handle opened by opendir.
• tie - Binds a variable to an object class, allowing method calls to be triggered by operations on the variable.
• tied - Returns a reference to the object underlying a tied variable.
• time - Returns the number of seconds since the Unix epoch (January 1, 1970, UTC).
• times - Returns elapsed CPU time for the current process and its children.
• tr/// - The transliteration (character replacement) operator. Can also be written as y///.
• truncate - Shortens a file to a specified length.
• uc - Returns an uppercased version of a string.
• ucfirst - Returns a string with its first character uppercased.
• umask - Sets or gets the file creation mode mask.
• undef - Undefines a variable or function, making its value undef.
• unlink - Deletes one or more files (removes links to files).
• unpack - Converts a binary string into a list of values according to a template.
• unshift - Prepends one or more elements to the beginning of an array.
• untie - Breaks the binding between a variable and its tied object class.
• use - Loads a module at compile time, importing symbols and running its import method.
• utime - Sets a file’s last access and modification times.
• values - Returns a list of all values from a hash.
• vec - Treats a string as a bit vector and allows testing or setting individual bits.
• wait - Waits for any child process to terminate.
• waitpid - Waits for a specific child process to terminate.
• wantarray - Returns true if the current subroutine call is in list context, false in scalar context, and undef in void context.
• warn - Prints a warning message to STDERR.
• write - Writes a formatted record to a filehandle using a declared format. Rarely used; see templating engines.
• -X (File Tests) - A set of unary operators that test file attributes (e.g., -r for readable, -x for executable, -f for plain file).
• y/// - An alias for the tr/// (transliteration) operator.