B.18 Built-in Functions

Perl has a great many built-in functions. Table B-6 is a partial list with short descriptions.

Table B-6. Perl built-in functions

Function	Summary
abs VALUE	Return the absolute value of its numeric argument
atan2 Y, X	Return the principal value of the arc tangent of Y/X from - to
chdir EXPR	Change the working directory to EXPR (or home directory by default)
chmod MODE LIST	Change the file permissions of the LIST of files to MODE
chomp (VARIABLE or LIST)	Remove ending newline from string(s), if present
chop (VARIABLE or LIST)	Remove ending character from string(s)
chown UID, GID, LIST	Change owner and group of LIST of files to numeric UID and GID
close FILEHANDLE	Close the file, socket, or pipe associated with FILEHANDLE
closedir DIRHANDLE	Close the directory associated with DIRHANDLE
cos EXPR	Return the cosine of the radian number EXPR
dbmclose HASH	Break the binding between a DBM file and a hash
dbmopen HASH, DBNAME, MODE	Bind a DBM file to a HASH with permissions given in MODE
defined EXPR	Return true or false if EXPR has a defined value or not
delete EXPR	Delete an element (or slice) from a hash or an array.
die LIST	Exit the program with an error message that includes LIST
each HASH	Step through a hash with one key, or key-value pair, at a time
exec PATHNAME LIST	Terminate the program and execute the program PATHNAME with arguments LIST
exists EXPR	Return true if hash key or array index exists
exit EXPR	Exit the program with the return value of EXPR
exp EXPR	Return the value of e raised to the exponent EXPR
format	Declare a format for use by the write function
grep EXPR, LIST	Return list of elements of LIST for which EXPR is true
gmtime	Get Greenwich mean time; Sunday is day 0, January is month 0, year is number of years since 1900—example: ($sec,$min,$hour,$mday,$mon,$year,$wday,$yday, $isdaylightsavingstime) = gmtime;
goto LABEL	Program control goes to statement marked with LABEL
hex EXPR	Return decimal value of hexadecimal EXPR
index STR, SUBSTR	Give the position of the first occurrence of SUBSTR in STR
int EXPR	Give the integer portion of the number in EXPR
join EXPR, LIST	Join the strings in LIST into a single string, separated by EXPR
keys HASH	Return a list of all the keys in HASH
last LABEL	Exit the immediately enclosing loop by default, or loop with LABEL
lc EXPR	Return a lowercased copy of string in EXPR
lcfirst EXPR	Return a copy of EXPR with first character lowercased
length EXPR	Return the length in characters of EXPR
localtime	Get local time in same format as in gmtime function
log EXPR	Return natural logarithm of number EXPR
m/PATTERN/	The match operator for the regular-expression PATTERN, often abbreviated as /PATTERN/
map BLOCK LIST (or map EXPR, LIST)	Evaluate BLOCK or EXPR for each element of LIST, return list of return values
mkdir FILENAME	Create the directory FILENAME
my EXPR	Localize the variables in EXPR to the enclosing block
next LABEL	Go to next iteration of enclosing loop by default or to loop marked with LABEL
oct EXPR	Return decimal value of octal value in EXPR
open FILEHANDLE, EXPR	Open a file by associating FILEHANDLE with the file and options given in EXPR
opendir DIRHANDLE, EXPR	Open the directory EXPR and assign handle DIRHANDLE
pop ARRAY	Remove and return the last element of ARRAY
pos SCALAR	Give location in string SCALAR where last m//g search left off
print FILEHANDLE LIST	Print LIST of strings to FILEHANDLE (default STDOUT)
printf FILEHANDLE FORMAT, LIST	Print string specified by FORMAT and variables LIST to FILEHANDLE
push ARRAY, LIST	Place the elements of LIST at the end of ARRAY
rand EXPR	Give pseudorandom decimal number from 0 to less than EXPR (default 1)
readdir DIRHANDLE	Return list of entries of directory DIRHANDLE
redo LABEL	Restart a loop block without reevaluating the conditional
ref EXPR	Return true or false if EXPR is a reference or not: if true, returned value indicates type of reference
rename OLDNAME, NEWNAME	Change the name of a file
return EXPR	Return from the current subroutine with value EXPR
reverse LIST	Give LIST in reverse order, or reverse strings in scalar context
rindex STR, SUBSTR	Like the index function but returns last occurrence of SUBSTR in STR
rmdir FILENAME	Delete the directory FILENAME
s/PATTERN/REPLACEMENT/	Replace the match of regular-expression PATTERN with string REPLACEMENT
scalar EXPR	Force EXPR to be evaluated in scalar context
seek FILEHANDLE, OFFSET, WHENCE	Position the file pointer for FILEHANDLE to OFFSET bytes (if WHENCE is 0, current position plus OFFSET if WHENCE is 1, or OFFSET bytes from the end if WHENCE is 2)
shift ARRAY	Remove and return the first element of ARRAY
sin EXPR	Return the sine of the radian number EXPR
sleep EXPR	Cause the program to sleep for EXPR seconds
sort USERSUB LIST (or sort BLOCK LIST)	Sort the LIST according to the order in USERSUB or BLOCK (default standard string order)
splice ARRAY, OFFSET, LENGTH, LIST	Remove LENGTH elements at OFFSET in ARRAY and replace with LIST, if present
split /PATTERN/, EXPR	Split the string EXPR at occurrences of /PATTERN/, return list
sprintf FORMAT, LIST	Return a string formatted as in the printf function
sqrt EXPR	Return the square root of the number EXPR.
srand EXPR	Set random number seed for rand operator; only needed in versions of Perl before 5.004
stat (FILEHANDLE or EXPR)	Return statistics on file EXPR or its FILEHANDLE—example: ($dev,$inode,$mode,$num_of_links,$uid,$gid,$rdev,$size,$accesstime, $modifiedtime,$changetime,$blksize,$blocks) = stat $filename;
study SCALAR	Try to optimize subsequent pattern matches on string SCALAR
sub NAME BLOCK	Define a subroutine named NAME with program code in BLOCK
substr EXPR, OFFSET, LENGTH,REPLACEMENT	Return substring of string EXPR at position OFFSET and length LENGTH; the substring is replaced with REPLACEMENT if used
system PATHNAME LIST	Execute any program PATHNAME with arguments LIST; returns exit status of program, not its output; to capture ouput, use backticks—example: @output = `/bin/who`;
tell FILEHANDLE	Return current file position in bytes in FILEHANDLE
tr/ORIGINAL/REPLACEMENT/	Transliterates each character in ORIGINAL with corresponding character in REPLACEMENT
truncate (FILEHANDLE or EXPR), LENGTH	Shorten file EXPR or opened with FILEHANDLE to LENGTH bytes
uc EXPR	Return uppercased version of string EXPR
ucfirst EXPR	Return string EXPR with first character capitalized
undef EXPR	Return the undefined value; if a defined variable or subroutine EXPR is given, it's no longer defined; it can be assigned a value when you don't need to save the value
unlink LIST	Delete the LIST of files
unshift ARRAY, LIST	Add LIST elements to the beginning of ARRAY
use MODULE	Load the MODULE
values HASH	Return a list of all values of the HASH
wantarray	In a subroutine, return true if calling program expects a list return value
warn LIST	Print error message including LIST
write FILEHANDLE	Write formatted record to FILEHANDLE (default STDOUT) as defined by the format function