Built-in Functions by Category#

The same built-ins as in the alphabetical index, grouped here by problem domain. A function may appear under more than one category: categories are a tag set, not a tree. Every link points at the same detail page regardless of which category the reader arrived through.

SCALARs and strings#

chomp - Strip the trailing input record separator from a string in place.
chop - Remove the last character from a string and return it.
chr - Return the character whose codepoint is the given number.
crypt - One-way passwd(5)-style hashing of a plaintext string with a salt.
fc - Return the Unicode casefolded form of a string for case-insensitive comparison.
hex - Interpret a string as a hexadecimal numeral and return its numeric value.
index - Find the position of a substring inside a string.
lc - Return a lowercased copy of a string.
lcfirst - Return a copy of a string with its first character lowercased.
length - Return the number of characters in a string.
oct - Interpret a string as a number written in octal, hexadecimal, or binary, and return the resulting integer.
ord - Return the Unicode code point of the first character of a string.
pack - Convert a list of Perl values into a binary string according to a template.
q// - Single-quoted string literal with a choice of delimiter.
qq// - Build a double-quoted, interpolated string with a delimiter you pick.
reverse - Reverse a list - or, in scalar context, reverse the characters of a string.
rindex - Find the position of the last occurrence of a substring inside a string.
sprintf - Build a formatted string from a format template and a list of values.
substr - Extract, replace, or alias a contiguous slice of a string.
tr/// - Character-by-character substitution. tr scans a string and replaces every occurrence of a character from SEARCHLIST with the positionally corresponding character from REPLACEMENTLIST, returning the count of characters it touched.
uc - Return an uppercased copy of a string.
ucfirst - Return a copy of a string with its first character titlecased.
y/// - Transliterate characters in a string. y/// is a synonym for tr/// - the two are identical in every respect.

Regular expressions and pattern matching#

m// - Search a string for a pattern and report whether - and what - it matched.
pos - Report or set where the next /g regex match will resume in a string.
qr// - Compile a pattern once and hand back a reusable regex object.
quotemeta - Return a copy of a string with every regex-significant character backslash-escaped, so the result can be interpolated into a pattern and match its own literal content.
s/// - Search a string for a pattern and replace every match with a replacement.
split - Cut a string into a list of fields using a regex separator.
study - A no-op retained for source compatibility with older Perl code.

Numeric functions#

abs - Return the absolute value of a number.
atan2 - Arc tangent of Y/X in the range -π to π.
cos - Return the cosine of a number given in radians.
exp - Raise e to a power.
hex - Interpret a string as a hexadecimal numeral and return its numeric value.
int - Return the integer portion of a number, truncating toward zero.
log - Return the natural logarithm (base e) of a number.
oct - Interpret a string as a number written in octal, hexadecimal, or binary, and return the resulting integer.
rand - Return a pseudo-random floating-point number in the half-open range [0, EXPR).
sin - Return the sine of a number given in radians.
sqrt - Return the non-negative square root of EXPR.
srand - Seed the pseudo-random number generator.

Arrays#

each - Step through a hash or array one entry at a time.
keys - List all keys of a hash, or all indices of an array.
pop - Remove and return the last element of an array.
push - Append one or more values to the end of an array.
shift - Remove and return the first element of an array.
splice - Remove and/or replace a slice of an array in place, and return the removed elements.
unshift - Prepend one or more values to the start of an array and return the array’s new length.
values - List every value of a hash (or every element of an array).

Lists#

all - Test whether BLOCK returns true for every element of LIST.
any - Return true if BLOCK yields true for at least one element of LIST.
grep - Filter a list to the elements where the block or expression is true.
join - Concatenate a list of strings with a separator between each adjacent pair, and return the single resulting string.
map - Apply a block or expression to each element of a list and return the flattened results.
qw// - Build a list of barewords by splitting a delimited string on whitespace, without quoting or comma-separating each word.
reverse - Reverse a list - or, in scalar context, reverse the characters of a string.
sort - Sort a list, returning the sorted list.
unpack - Extract typed values from a binary or fixed-width string according to a template.

Hashes#

delete - Remove the named key-value pair(s) from a hash, or element(s) from an array, and return what was removed.
each - Step through a hash or array one entry at a time.
exists - Test whether a hash or array element, or a named subroutine, is present - without creating it and without caring what it holds.
keys - List all keys of a hash, or all indices of an array.
values - List every value of a hash (or every element of an array).

I/O#

binmode - Set the I/O layer stack on a filehandle - typically to make it deliver raw bytes, or to attach a character encoding.
close - Close a filehandle, flush its buffers, and release the underlying file descriptor.
closedir - Close a directory handle opened by opendir.
dbmclose - Break the binding between a DBM file and a hash previously attached by dbmopen.
dbmopen - Bind a DBM file on disk to a hash so hash reads and writes become lookups and stores in the database.
die - Raise an exception.
eof - Test a filehandle for end-of-file.
fileno - Return the OS-level file descriptor number behind a filehandle.
flock - Place an advisory lock on an open file.
format - Declare a picture-based report template for use by write.
getc - Read the next single character from a filehandle.
print - Write a list of values to a filehandle.
printf - Write a formatted string to a filehandle.
read - Read a fixed amount of buffered input from a filehandle into a scalar.
readdir - Read the next entry, or all remaining entries, from a directory handle opened by opendir.
readline - Read one or more records from a filehandle.
rewinddir - Reset a directory handle to the start of its listing.
say - Print a list of values followed by a newline.
seek - Reposition a filehandle for random-access reads or writes.
seekdir - Restore a directory handle to a position previously captured by telldir.
select - Either set the default output filehandle, or call the select(2) syscall for I/O multiplexing. Same name, two unrelated jobs - disambiguated by argument count.
syscall - Invoke a raw system call by its kernel number, passing the remaining arguments as int or as a pointer to a string buffer.
sysread - Read raw bytes from a filehandle by calling the underlying read(2) system call.
sysseek - Reposition a filehandle at the system level, bypassing PerlIO buffering.
syswrite - Write bytes to a filehandle with the raw write(2) system call, bypassing Perl’s buffered I/O.
tell - Return the current byte position of a filehandle.
telldir - Return the current read position of a directory handle as an opaque token.
truncate - Shorten (or extend) a file to an exact byte length.
warn - Emit a warning to STDERR.
write - Render one record to a filehandle through its associated format.

Fixed-length data#

pack - Convert a list of Perl values into a binary string according to a template.
read - Read a fixed amount of buffered input from a filehandle into a scalar.
syscall - Invoke a raw system call by its kernel number, passing the remaining arguments as int or as a pointer to a string buffer.
sysread - Read raw bytes from a filehandle by calling the underlying read(2) system call.
sysseek - Reposition a filehandle at the system level, bypassing PerlIO buffering.
syswrite - Write bytes to a filehandle with the raw write(2) system call, bypassing Perl’s buffered I/O.
unpack - Extract typed values from a binary or fixed-width string according to a template.
vec - Read or write a fixed-width slot inside a string treated as a packed bit vector.

Filehandles, files, directories#

chdir - Change the process’s current working directory.
chmod - Change the permission bits of a list of files.
chown - Change the owner and group of a list of files.
chroot - Change the root directory of the current process and every child it later spawns.
fcntl - Perform a fcntl(2) file-control operation on a filehandle.
glob - Expand a shell-style filename pattern into the list of matching paths.
ioctl - Perform a device-control ioctl(2) system call on a filehandle.
link - Create a hard link from NEWFILE to the existing OLDFILE.
lstat - Return the 13-element status list for a path without following a symbolic link.
mkdir - Create a single directory on the filesystem.
open - Associate a filehandle with a file, a command, or an in-memory scalar.
opendir - Open a directory for reading.
readlink - Return the target path a symbolic link points to.
rename - Change the name of a file.
rmdir - Remove an empty directory.
select - Either set the default output filehandle, or call the select(2) syscall for I/O multiplexing. Same name, two unrelated jobs - disambiguated by argument count.
stat - Get a file’s status information.
symlink - Create a symbolic link at NEWFILE that points at the string OLDFILE.
sysopen - Open a file the low-level way, passing an integer MODE bitmask straight through to the underlying open(2) system call.
umask - Set or read the process file-creation mode mask.
unlink - Remove one or more directory entries that name files.
utime - Set access and modification times on a list of files.

Control flow#

__FILE__ - The name of the source file the token is compiled in.
__LINE__ - A compile-time token that evaluates to the line number at which it appears in the source.
__PACKAGE__ - Return the name of the package currently in effect at the point where the token appears.
__SUB__ - Return a reference to the currently executing subroutine.
break - Break out of a given block.
caller - Return information about the subroutine, eval, or require that called the currently executing code.
catch - Handle an exception thrown by a preceding try block.
continue - Attach a block to a loop that runs after every iteration, just before the condition is re-tested.
defer - Schedule a block to run when the enclosing scope exits, for any reason.
die - Raise an exception.
do - Execute a block of code or run a Perl source file as if it were part of the current program.
dump - Cause the running program to produce a core dump immediately.
eval - Run a piece of Perl code with any fatal error trapped instead of killing the program.
evalbytes - Compile and run a string of Perl source, forcing the source to be interpreted as bytes rather than characters.
exit - Terminate the program with a status value.
finally - Run cleanup code on the way out of a try/catch, whether the body succeeded, threw, or jumped away.
goto - Transfer execution elsewhere in the program without returning.
last - Exit a loop immediately, skipping the rest of the body and the continue block.
method - Declare a named instance method inside a class block.
next - Start the next iteration of the enclosing loop immediately.
redo - Restart the current iteration of a loop without re-testing the condition and without running the continue block.
return - Leave the current subroutine, eval, do FILE, sort block, or regex eval block, yielding a value to the caller.
sub - Declare or define a subroutine.
try - Run a block and divert any exception it throws into a catch block, with an optional finally block that always runs on the way out.
wantarray - Report the calling context of the currently executing subroutine.

Scoping#

caller - Return information about the subroutine, eval, or require that called the currently executing code.
class - Declare a namespace that behaves as a native object class.
field - Declare a per-instance variable inside a class block.
import - Populate the caller’s namespace with names a module chooses to export.
local - Save the current value of a package variable and restore it when the enclosing scope exits.
my - Declare one or more lexically scoped variables.
our - Declare a lexically scoped alias to a package variable.
package - Declare the compile-time namespace for the declarations that follow.
state - Declare a lexically scoped variable whose value persists across calls to its enclosing subroutine.
use - Load a module at compile time and import its symbols into the current package.

Misc#

defined - Test whether a value, variable, or subroutine is defined.
formline - Format a list of values into a picture string and append the result to the format accumulator $^A.
lock - Place an advisory lock on a shared variable, array, hash, or subroutine until the lock goes out of scope.
prototype - Return the prototype string of a subroutine, or undef if it has none.
reset - Clear every package variable whose name begins with one of a set of letters, and re-arm one-shot m?pattern? matches.
scalar - Force EXPR to be evaluated in scalar context and return its value.
undef - The undefined value, and the operator that produces it.

Processes#

alarm - Schedule a SIGALRM to be delivered to the current process after a whole number of wallclock seconds.
exec - Abandon this program and run another in the same process.
fork - Create a new process running the same program at the same point.
getpgrp - Return the POSIX process-group ID that a process belongs to.
getppid - Return the process ID of the current process’s parent.
getpriority - Return the current scheduling nice value of a process, a process group, or a user.
kill - Send a signal to a list of processes.
pipe - Open a pair of connected filehandles - one for reading, one for writing.
qx// - Run a shell command and capture its standard output.
readpipe - Run a shell command and return its standard output.
setpgrp - Set the process group of a process.
setpriority - Set the scheduling priority (nice value) of a process, process group, or user.
sleep - Pause the process for a number of whole seconds.
system - Run a separate program and wait for it to finish.
times - Report CPU time consumed by this process and its terminated children.
wait - Block until any child process exits and reap it.
waitpid - Wait for a specific child process to terminate and reap it.

Modules#

do - Execute a block of code or run a Perl source file as if it were part of the current program.
import - Populate the caller’s namespace with names a module chooses to export.
no - The compile-time inverse of use - call a module’s unimport method to turn off what use turned on.
package - Declare the compile-time namespace for the declarations that follow.
require - Load a Perl source file at runtime, or demand a minimum Perl version.
use - Load a module at compile time and import its symbols into the current package.

Classes and OO#

__CLASS__ - Return the class name of the instance currently being acted on.
bless - Mark the thing a reference points at as an object in a package.
class - Declare a namespace that behaves as a native object class.
dbmclose - Break the binding between a DBM file and a hash previously attached by dbmopen.
dbmopen - Bind a DBM file on disk to a hash so hash reads and writes become lookups and stores in the database.
field - Declare a per-instance variable inside a class block.
isa - Test whether an object is an instance of a class or of any subclass derived from it.
method - Declare a named instance method inside a class block.
package - Declare the compile-time namespace for the declarations that follow.
ref - Return a string describing what a reference points to.
tie - Bind a variable to a class so that every access to the variable dispatches through that class’s methods.
tied - Return the object backing a tied variable.
untie - Break the binding between a variable and its tied class.
use - Load a module at compile time and import its symbols into the current package.

Sockets#

accept - Accept an incoming connection on a listening socket.
bind - Attach a local address to a socket.
connect - Initiate a connection from a socket to a remote address.
getpeername - Return the address of the remote end of a connected socket.
getsockname - Return the local address of a connected or bound socket.
getsockopt - Read one socket option out of the kernel as an opaque packed string.
listen - Mark a socket as passive so it can accept incoming connections.
recv - Read an incoming message from a socket into a scalar.
send - Send a message on a socket.
setsockopt - Set a kernel-level option on an open socket.
shutdown - Shut down one direction of a socket connection, or both.
socket - Create a socket filehandle.
socketpair - Create an unnamed, connected pair of sockets that talk to each other.

SysV IPC#

msgctl - Perform a control operation on a System V IPC message queue.
msgget - Create or look up a System V IPC message queue and return its id.
msgrcv - Receive a message from a System V IPC message queue.
msgsnd - Send a message to a System V IPC message queue.
semctl - Perform a control operation on a System V semaphore set.
semget - Create or look up a System V semaphore set and return its identifier.
semop - Perform one or more System V semaphore operations atomically.
shmctl - Control or query a System V shared memory segment.
shmget - Create or look up a System V shared memory segment and return its identifier.
shmread - Copy bytes out of a System V shared memory segment into a Perl scalar.
shmwrite - Copy bytes into a System V shared memory segment.

User and group info#

endgrent - Close the group database after iterating it.
endpwent - Close the passwd-database iterator opened by getpwent or setpwent.
getgrent - Read the next entry from the system group database.
getgrgid - Look up a group record by numeric group ID.
getgrnam - Look up a Unix group by name and return its /etc/group record.
getlogin - Return the login name of the user associated with the controlling terminal.
getpwent - Return the next entry from the system password database.
getpwnam - Look up a user’s passwd record by login name.
getpwuid - Look up a user’s passwd record by numeric UID.
setgrent - Rewind the group-database iterator back to the first entry.
setpwent - Rewind the password-database iterator so the next getpwent call returns the first entry again.

Network info#

endhostent - Close the hosts database after iteration.
endnetent - Close the networks database after iteration.
endprotoent - Close the protocols database after iteration.
endservent - Close the services database after a walk with getservent.
gethostbyaddr - Look up a host record by its packed IP address.
gethostbyname - Look up a host record by DNS name.
gethostent - Fetch the next entry from the host database.
getnetbyaddr - Look up a network record by its numeric network address.
getnetbyname - Look up a network record by name.
getnetent - Read the next entry from the networks database.
getprotobyname - Look up an IP protocol by its textual name and return its database entry.
getprotobynumber - Look up a network protocol entry by its assigned protocol number.
getprotoent - Fetch the next entry from the protocols database.
getservbyname - Look up a network service by its textual name and protocol.
getservbyport - Look up a network service by its numeric port and protocol.
getservent - Read the next entry from the system services database.
sethostent - Open or rewind the hosts database for iteration.
setnetent - Open or rewind the networks database for iteration.
setprotoent - Open the protocols database and prepare it for sequential reads.
setservent - Rewind the services database and optionally keep it open across lookups.

Time#

gmtime - Convert an epoch time to a broken-down UTC time, either as a 9-element list or as a ctime(3)-style string.
localtime - Convert an epoch time to a broken-down calendar time in the local time zone.
time - Return the current wall-clock time as an integer number of seconds since the system epoch.
times - Report CPU time consumed by this process and its terminated children.