Perl has a large number of functions that come as standard with most implementations, and an even wider range of additional modules, each with its own additional functions. This chapter lists all the standard functions alphabetically for reference.
Each function is assigned a category. There are two main categories; list operators, which can take more than one argument, and named unary operators, which can only take one argument. A secondary category is noted in parentheses so you can see, at a glance, the type of operation the function performs. This is a very rough categorization, as many functions might overlap in any category scheme.
For each function the form of the arguments is listed. If there are multiple forms of calling the function, there will be multiple lines describing each form. The meanings of the arguments are described in the text.
The type of value returned by the function is listed. This is usually specified in more detail in the function description.
Two categories of functions, those dealing with sockets and those dealing with System V inter-process communications, are not dealt with in great detail. Both of these categories of functions are direct counterparts of UNIX system functions.
Category named unary operator (file test)
Arguments handle
Arguments filename
Arguments none
Return Value integer (age of file in days since last
access relative to $BASETIME)
The file test operator takes one file handle or filename as an argument. It returns age of file in days since last access relative to $BASETIME. All file test operators can take a special argument underscore, which means that the test is carried out on the same file handle as the last file test, stat(), or lstat() call. If no argument is supplied, $_ is used.
print "-A ", -A "/etc/fstab", "\n";
Category named unary operator (file test) Arguments handle Arguments filename Arguments none Return Value 1 (true) '' (false)
The file test operator takes one file handle or filename as an argument. It returns 1 (true) if the file is binary. It returns '' (false) if the file is not binary. The first characters of the file are checked to see if the high bit is set and if a suitable number do have the high bit set the file is assumed to be binary. If the file is empty it is returned as binary. Because this test involves reading the file itself, it is best to test to learn if the file exists as a plain file (-f), first. All file test operators can take a special argument underscore, which means that the test is carried out on the same file handle as the last file test, stat(), or lstat() call. If no argument is supplied, $_ is used.
(-B "/etc/fstab") ? print("-B fstab is binary\n") :
print("-B fstab is not binary\n");
Category named unary operator (file test) Arguments handle Arguments filename Arguments none Return Value 1 (true) '' (false)
The file test operator takes one file handle or filename as an argument. It returns 1 (true) if the file is a block special file (that is, a UNIX /dev device file). It returns '' (false) if the file is not a block special file. All file test operators can take a special argument underscore, which means that the test is carried out on the same file handle as the last file test, stat(), or lstat() call. If no argument is supplied, $_ is used.
(-b "/dev/hda1") ? print("-b hda1 is block\n") :
print("-b hda1 is not block\n");
Category named unary operator (file test)
Arguments handle
Arguments filename
Arguments none
Return Value integer (age of file in days since last
inode change relative to $BASETIME)
The file test operator takes one file handle or filename as an argument. It returns age of file in days since last inode change relative to $BASETIME. All file test operators can take a special argument underscore, which means that the test is carried out on the same file handle as the last file test, stat(), or lstat() call. If no argument is supplied, $_ is used.
print "-C ", -C "/etc/fstab", "\n";
Category named unary operator (file test) Arguments handle Arguments filename Arguments none Return Value 1 (true) '' (false)
The file test operator takes one file handle or filename as an argument. It returns 1 (true) if the file is a character special file. It returns '' (false) if the file is not a character special file. All file test operators can take a special argument underscore, which means that the test is carried out on the same file handle as the last file test, stat(), or lstat() call. If no argument is suppligª, $_ is used.
(-c "/dev/tty0") ? print("-c tty0 is char\n") :
print("-c tty0 is not char\n");
Category named unary operator (file test) Arguments handle Arguments filename Arguments none Return Value 1 (true) '' (false)
The file test operator takes one file handle or filename as an argument. It returns 1 (true) if the file is a directory. It returns '' (false) if the file is not a directory. All file test operators can take a special argument underscore, which means that the test is carried out on the same file handle as the last file test, stat(), or lstat() call. If no argument is supplied, $_ is used.
(-d "/") ? print("-d / is dir\n") : print("-d / is not dir\n");
Category named unary operator (file test) Arguments handle Arguments filename Arguments none Arguments none Return Value 1 (true) '' (false)
The file test operator takes one file handle or filename as an argument. It returns 1 (true) if file exists. It returns '' (false) if the file does not exist. All file test operators can take a special argument underscore, which means that the test is carried out on the same file handle as the last file test, stat(), or lstat() call. If no argument is supplied, $_ is used.
(-e "/") ? print("-e / exists\n") : print("-e / exists\n");
Category named unary operator (file test) Arguments handle Arguments filename Arguments none Return Value 1 (true) '' (false)
The file test operator takes one file handle or filename as an argument. It returns 1 (true) if the file is a plain file. It returns '' (false) if the file is not a plain file. A plain file is any file that is not a special block device (-b), a special character device (-c), a directory (-d), a symbolic link (-l), a pipe (-p), a named socket (-S), or a direct link to an I/O terminal (-t). All file test operators can take a special argument underscore, which means that the test is carried out on the same file handle as the last file test, stat(), or lstat() call. If no argument is supplied, $_ is used.
(-f "/") ? print("-f / is plain\n") : print("-f / is not plain\n");
Category named unary operator (file test) Arguments handle Arguments filename Arguments none Return Value 1 (true) '' (false)
The file test operator takes one file handle or filename as an argument. It returns 1 (true) if the file has the setgid bit set. It returns '' (false) if the file does not have the setgid bit set. In UNIX, setgid allows an executable to run as if it was being run by the group, which owns the executable itself while executing (for example, if a binary is owned by the group wwwstat, and the binary has the getgid bit set, then that binary has access to all files that the wwwstat group can access while the binary is running, even when the binary is run by someone who is not actually a member of the wwwstat group). All file test operators can take a special argument underscore, which means that the test is carried out on the same file handle as the last file test, stat(), or lstat() call. If no argument is supplied, $_ is used.
(-g "/vmlinuz") ? print("-g /vmlinuz has setgid\n") :
print("-g /vmlinuz has not setgid\n");
Category named unary operator (file test) Arguments handle Arguments filename Arguments none Return Value 1 (true) '' (false)
The file test operator takes one file handle or filename as an argument. It returns 1 (true) if the sticky bit is set. It returns '' (false) if the sticky bit is not set. In UNIX, the sticky bit can mark an executable file to be held in memory when exited (for example, if the binary ls is marked as sticky, when the first person runs it, it is loaded from disk to memory and executed, but when the execution finishes, the binary stays in memory so that when the next person runs ls it does not need to be loaded into memory again because it is already there). This is normally set for frequently used commands to optimize execution speed. All file test operators can take a special argument underscore, which means that the test is carried out on the same file handle as the last file test, stat(), or lstat() call. If no argument is supplied, $_ is used.
(-k "/vmlinuz") ? print("-k /vmlinuz is sticky\n") :
print("-k /vmlinuz is not sticky\n");
Category named unary operator (file test) Arguments handle Arguments filename Arguments none Return Value 1 (true) '' (false)
The file test operator takes one file handle or filename as an argument. It returns 1 (true) if the file is a symbolic link. It returns '' (false) if the file is not a symbolic link. All file test operators can take a special argument underscore, which means that the test is carried out on the same file handle as the last file test, stat(), or lstat() call. If no argument is supplied, $_ is used.
(-l "/vmlinuz") ? print("-l /vmlinuz is symlink\n") :
print("-l /vmlinuz is not symlink\n");
Category named unary operator (file test) Arguments handle Arguments filename Arguments none Return Value integer (age of file in days relative to $BASETIME)
The file test operator takes one file handle or filename as an argument. It returns the age of the file in days relative to $BASETIME. All file test operators can take a special argument underscore, which means that the test is carried out on the same file handle as the last file test, stat(), or lstat() call. If no argument is supplied, $_ is used.
print "-M ", -M "/etc/fstab", "\n";
Category named unary operator (file test) Arguments handle Arguments filename Arguments none Return Value 1 (true) '' (false)
The file test operator takes one file handle or filename as an argument. It returns 1 (true) if the file is owned by the real UID/GID and it returns '' (false) otherwise. For the superuser it always returns true. All file test operators can take a special argument underscore, which means that the test is carried out on the same file handle as the last file test, stat(), or lstat() call. If no argument is supplied, $_ is used.
(-o "/vmlinuz") ? print("-o /vmlinuz is owned by real uid/gid\n") :
print("-o /vmlinuz is not owned by real uid/gid\n");
Category named unary operator (file test) Arguments handle Arguments filename Arguments none Return Value 1 (true) '' (false)
The file test operator takes one file handle or filename as an argument. This function returns 1 (true) if the file is owned by the effective UID/GID and it returns '' (false) otherwise. For the superuser it always returns true. All file test operators can take a special argument underscore, which means that the test is carried out on the same file handle as the last file test, stat(), or lstat() call. If no argument is supplied, $_ is used.
(-O "/vmlinuz") ? print("-O /vmlinuz is owned by effective uid/gid\n") :
print("-o /vmlinuz is not owned by effective uid/gid\n");
Category named unary operator (file test) Arguments handle Arguments filename Arguments none Return Value 1 (true) '' (false)
The file test operator takes one file handle or filename as an argument. It returns 1 (true) if the file is a named pipe. It returns '' (false) if the file is not a named pipe. All file test operators can take a special argument underscore, which means that the test is carried out on the same file handle as the last file test, stat(), or lstat() call. If no argument is supplied, $_ is used.
(-p "/vmlinuz") ? print("-p /vmlinuz is named pipe\n") :
print("-p /vmlinuz is not named pipe\n");
Category named unary operator (file test) Arguments handle Arguments filename Arguments none Return Value 1 (true) '' (false)
The file test operator takes one file handle or filename as an argument. It returns 1 (true) if the file is readable by the effective UID/GID and it returns '' (false) otherwise. For the superuser it always returns true. All file test operators can take a special argument underscore, which means that the test is carried out on the same file handle as the last file test, stat(), or lstat() call. If no argument is supplied, $_ is used.
(-R "/vmlinuz") ? print("-R /vmlinuz is readable by effective uid/gid\n") :
print("-R /vmlinuz is not readable by effective uid/gid\n");
Category named unary operator (file test) Arguments handle Arguments filename Arguments none Return Value 1 (true) '' (false)
The file test operator takes one file handle or filename as an argument. It returns 1 (true) if the file is readable by the real UID/GID and it returns '' (false) otherwise. For the superuser it always returns true. All file test operators can take a special argument underscore, which means that the test is carried out on the same file handle as the last file test, stat(), or lstat() call. If no argument is supplied, $_ is used.
(-r "/vmlinuz") ? print("-r /vmlinuz is readable by real uid/gid\n") :
print("-r /vmlinuz is not readable by real uid/gid\n");
Category named unary operator (file test) Arguments handle Arguments filename Arguments none Return Value 1 (true) '' (false)
The file test operator takes one file handle or filename as an argument. It returns 1 (true) if the file is a symbolic link. It returns '' (false) if the file is not a symbolic link. All file test operators can take a special argument underscore, which means that the test is carried out on the same file handle as the last file test, stat(), or lstat() call. If no argument is supplied, $_ is used.
(-S "/vmlinuz") ? print("-S /vmlinuz is socket\n") :
print("-S /vmlinuz is not socket\n");
Category named unary operator (file test) Arguments handle Arguments filename Arguments none Return Value integer (size) '' (false)
The file test operator takes one file handle or filename as an argument. It returns size in bytes as an integer if the file has a non-zero size. It returns '' (false) if the file has zero size. All file test operators can take a special argument underscore, which means that the test is carried out on the same file handle as the last file test, stat(), or lstat() call. If no argument is supplied, $_ is used.
(-s "/vmlinuz") ? print("-s /vmlinuz has non-zero size\n") :
print("-s /vmlinuz does not have non-zero size\n");
Category named unary operator (file test) Arguments handle Arguments filename Arguments none Return Value 1 (true) '' (false)
The file test operator takes one file handle or filename as an argument. It returns 1 (true) if the file is a text file. It returns '' (false) if the file is not a text file. The first characters of the file are checked to see if the high bit is set, and if a suitable number is not set the file is assumed to be text. If the file is empty, true is returned. Because this test involves reading the file itself, it is best to test to learn if the file exists as a plain file (-f) first. All file test operators can take a special argument underscore, which means that the test is carried out on the same file handle as the last file test, stat(), or lstat() call. If no argument is supplied, $_ is used.
(-T "/vmlinuz") ? print("-T /vmlinuz is text file\n") :
print("-T /vmlinuz is not text file\n");
Category named unary operator (file test) Arguments handle Arguments filename Arguments none Return Value 1 (true) '' (false)
The file test operator takes one file handle or filename as an argument. It returns 1 (true) if the file is a terminal tty device. It returns '' (false) if the file is not. All file test operators can take a special argument underscore, which means that the test is carried out on the same file handle as the last file test, stat(), or lstat() call. If no argument is supplied, STDIN is used.
(-t "/vmlinuz") ? print("-t /vmlinuz is tty\n") :
print("-t /vmlinuz is not tty\n");
Category named unary operator (file test) Arguments handle Arguments filename Arguments none Return Value 1 (true) '' (false)
The file test operator takes one file handle or filename as an argument. It returns 1 (true) if the file has the setuid bit set. It returns '' (false) if the files does not have the setuid bit set. In UNIX, setuid allows an executable to take on the uid of the user ownership of the executable itself while executing. All file test operators can take a special argument underscore, which means that the test is carried out on the same file handle as the last file test, stat(), or lstat() call. If no argument is supplied, $_ is used.
(-u "/vmlinuz") ? print("-u /vmlinuz has suid set\n") :
print("-u /vmlinuz does not have suid set\n");
Category named unary operator (file test) Arguments handle Arguments filename Arguments none Return Value 1 (true) '' (false)
The file test operator takes one file handle or filename as an argument. It returns 1 (true) if the file is writable by the real uid/gid. It returns '' (false) otherwise. For the superuser it always returns true. All file test operators can take a special argument underscore, which means that the test is carried out on the same file handle as the last file test, stat(), or lstat() call. If no argument is supplied, $_ is used.
(-W "/vmlinuz") ? print("-W /vmlinuz is writable by real uid/gid\n") :
print("-W /vmlinuz is not writable by real UID/GID\n");
Category named unary operator (file test) Arguments handle Arguments filename Arguments none Return Value 1 (true) '' (false)
The file test operator takes one file handle or filename as an argument. It returns 1 (true) if the file is writable by the effective uid/gid. It returns '' (false) otherwise. For the superuser it always returns true. All file test operators can take a special argument underscore, which means that the test is carried out on the same file handle as the last file test, stat(), or lstat() call. If no argument is supplied, $_ is used.
(-w "/vmlinuz") ? print("-w /vmlinuz is writable by effective uid/gid\n") :
print("-l /vmlinuz is not writable by effective uid/gid\n");
Category named unary operator (file test) Arguments handle Arguments filename Arguments none Return Value 1 (true) '' (false)
The file test operator takes one file handle or filename as an argument. It returns 1 (true) if the file is executable by the real uid/gid. It returns '' (false) otherwise. For the superuser it always returns true. All file test operators can take a special argument underscore, which means that the test is carried out on the same file handle as the last file test, stat(), or lstat() call. If no argument is supplied, $_ is used.
(-X _) ? print("-X /bin/ls is executable by real uid/gid\n") :
print("-X /bin/ls is not executable by real uid/gid\n");
Category named unary operator (file test) Arguments handle Arguments filename Arguments none Return Value 1 (true) '' (false)
The file test operator takes one file handle or filename as an argument. It returns 1 (true) if the file is executable by the effective uid/gid. It returns '' (false) otherwise. For the superuser it always returns true. All file test operators can take a special argument underscore, which means that the test is carried out on the same file handle as the last file test, stat(), or lstat() call. If no argument is supplied, $_ is used.
(-x "/bin/ls") ? print("-x /bin/ls is executable by effective uid/gid\n") :
print("-x /bin/ls is not executable by effective uid/gid\n");
Category named unary operator (file test) Arguments handle Arguments filename Arguments none Return Value 1 (true) '' (false)
The file test operator takes one file handle or filename as an argument. It returns 1 (true) if the file has zero size. It returns '' (false) otherwise. All file test operators can take a special argument underscore, which means that the test is carried out on the same file handle as the last file test, stat() or lstat() call. If no argument is supplied, $_ is used.
(-z "/vmlinuz") ? print("-z /vmlinuz has zero size\n") :
print("-z /vmlinuz does not have zero size\n");
Category named unary operator (numeric) Arguments numeric value Return Value numeric
This function returns the absolute value of its argument (it ignores any sign).
print("abs(-10) = ",abs(-10),"\n");
Category list operator (socket) Arguments newsocket, genericsocket Return Value integer (address of socket), '' (false)
This function performs the low-level UNIX socket call accept().
Category named unary operator (process) Arguments integer (seconds) Return Value integer (seconds to previous alarm)
This function sets up a UNIX SIGALRM signal to be generated in the number of seconds specified. It is possible for Perl to trap such signals by calling specific signal handling subroutines, such as trap(). Subseqent calls reset the alarm() time, retaining the number of seconds which were needed before the previous SIGALRM would have been generated. A call with zero seconds as an argument cancels the current alarm().
print("alarm(10) ",alarm(10),
" (to illustrate it needs to trapped c.f. trap)\n");
Category list operator (numeric) Arguments numeric, numeric Return Value numeric
The atan2 function returns the arctangent of the arguments.
print("atan2(60,2) = ",atan2(60,2),"\n");
Category list operator (socket) Arguments sockethandle, numeric (network address) Return Value 1 (true) '' (false)
This function binds a network address to the socket handle, see the UNIX bind() call.
Category named unary operator (i/o) Arguments handle Return Value 1 (success) or undefined (error)
On systems that distinguish between text and binary files, this function forces binary mode treatment of the given file handle. In systems which do make the distinction, text files have the end of line characters (Carriage Return, Linefeed) automatically translated to the UNIX end of line character (Linefeed) when reading from the file (and vice versa when writing to the file); binary mode files do not have this automatic transformation.
open(FIL,"file.dat"); binmode(FIL);
Category list operator (class) Arguments variable Arguments variable, classname Return Value reference
This function assigns a class to the referenced object. This class
is either explicitly stated in the call, or the name of the current
package is used if a second argument is not used in the call.
The reference is returned.
| TIP |
Explictly state the class (use the two-argument version of the call) if the code can be inherited by other classes, because the class in the single-argument call would not return the required value. |
$tmp = {};
bless $tmp, ATMPCLASS;
print "bless() \$tmp is now in class ",ref($tmp),"\n";
Category named unary operator (scope) Arguments expression Arguments none Return Value 1 (true) '' (false) Return Value (package, filename, line)
This function is used to test the current scope of a subroutine call. If evaluated in a scalar context, it returns 1 or '' depending on if the current code has been called as a subroutine (this includes code which is included using a require() or an eval() call). In an array context it supplies details of the calling context in a list comprising the package name, filename, and line of the call.
sub testcaller {
($package, $file, $line) = caller;
}
&testcaller;
print "caller() Package=$package File=$file Line=$line \n";
Category named unary operator (files) Arguments expression Arguments none Return Value 1 (true) '' (false)
This function changes the current directory to the directory specified. If no argument is given this call changes the current directory to be the home directory of the current user. It returns 1 upon success and '' otherwise.
chdir("/") ? print("It worked.\n") : print("It didn't work.\n");
Category list operator (files) Arguments list Return Value numeric
The first element in the list is the UNIX octal number representing the file permission. This function applies the mode specified by the octal number to all the files in the list that follows. It returns the number of files successfully modified.
print "chmod() changed ", chmod(0744,"/tmp/test1.txt","/tmp/test2.txt")," files.\n";
Category list operator (string) Arguments list Arguments variable Arguments none Return Value numeric
This is an alternative to the chop() function. It removes characters at the end of strings corresponding to the $INPUT_LINE_SEPARATOR ($/). It returns the number of characters removed. It can be given a list of strings upon which to perform this operation. When given no arguments, the operation is performed on $_.
$tmp="Aaagh!\n";
$ret = chomp $tmp;
print("chomp() ", $tmp, " returned ", $ret, "\n");
Category list operator (string) Arguments list Arguments variable Arguments none Return Value character
This function removes the last character of a string and returns that character. If given a list of arguments, the operation is performed on each one and the last character chopped is returned.
$tmp = "1234";
$ret = chop $tmp;
print("chop() ", $tmp, " returned ", $ret, "\n");
| TIP |
Use chomp() (with $/ set to "\n") rather than chop() if you are unsure that the string has a trailing newline because chop() will remove the last character regardless, but chomp()only removes it if it is a newline. |
Category list operator (files) Arguments list Return Value numeric
This function changes the ownership of the specified files. The first two elements of the list define the user ID and the group ID to set this ownership; the subsequent items in the list are the file names that are changed. The return value is the number of files successfully changed.
print("chown() ");
chown(1,1,"/tmp/test1.txt") ? print("Worked\n") : print("Didn't work\n");
Category named unary operator (string) Arguments numeric Return Value character
This function returns the character indicated by the numeric argument.
$E = chr(69);
print("chr() $E \n");
Category named unary operator (files) Arguments directoryname Arguments none Return Value 1 (true) '' (false)
This function is equivalent to the UNIX chroot() function.
Given a directory name, this directory is treated as the root
directory by all subseqent file system references, thus effectively
hiding the rest of the file system outside the specified directory.
This restriction applies to all subprocesses of the current process
as well.
| TIP |
Normal UNIX security limits this function to the superuser, and it is normally used to make processes safer by only allowing them access to the subdirectory tree relevant to their purpose. |
print("chroot() ");
chroot("/") ? print("Worked.\n") : print("Didn't work.\n");
Category named unary operator (files) Arguments handle Return Value 1 (true) '' (false)
This function closes the file opened with the file handle. This operation flushes all buffered output. If the file handle refers to a pipe, the Perl program waits until the process being piped has finished.
open(INF,"/tmp/test1.txt");
$ret = close(INF);
print("close() Returned ",$ret," on success\n");
Category named unary operator (file) Arguments handle Return Value 1 (true) '' (false)
This function closes the directory opened by opendir() by specifying the relevant directory handle.
opendir(IND,"/tmp");
$ret = closedir(IND);
print("closedir() Returned ",$ret," on success\n");
Category list operator (socket) Arguments socket, name Return Value 1 (true) '' (false)
This function is equivalent to the UNIX function call, which initiates a connection with a process, assuming that the process that is connected is waiting to accept.
Category flow control Arguments block Return Value n/a
A continue block is a syntax structure that allows a condition to be attached to another block (normally a while block). Any statements in the continue block are evaluated before the attached block is repeated.
$i=0;
print "continue() ";
while ($i<10) {
if ($i % 2)
{ print "${i}o "; next; }
else
{print "${i}e ";}
} continue {$i++}
print "\n";
Category named unary operator (numeric) Arguments expression Return Value numeric
This function returns the cosine value of the numeric expression supplied as an argument.
print "cos() ",cos(60),"\n";
Category list operator Arguments string, string Return Value string
This function is equivalent to the crypt() UNIX call (where available). It encrypts a string (the first argument) using a key (usually the first two letters of the first string itself) and returns the encrypted string.
print "crypt() Password PA: ",crypt("Password","PA"),"\n";
Category named unary operator (i/o) Arguments arrayname Return Value 1 (true) '' (false)
This function undoes the linking of an associative array to a
dbm file (see dbmopen()).
| NOTE |
This is depreciated in Perl 5; use untie() instead. |
Category list operator (i/o) Arguments arrayname, dbname, mode Return Value fatal error if dbm not supported (Perl 4)
This function links the associative array referred to by arrayname, to the dbm database (or equivalent) referred to by dbname (this name should not include the suffix). If the database does not exist, a new one with the specified mode will be opened (the mode being an octal chmod() style file protection).
This is depreciated in Perl 5; use tie() instead.
Category named unary operator (misc) Arguments expression Return Value 1 (true) '' (false)
This function returns a Boolean value depending on whether the argument is defined or not. There is a subtle distinction between an undefined and a defined null value. Some functions return an undefined null to indicate errors, while others return a defined null to indicate a particular result (use a comparison with the null string to test for this, rather than using defined())
@iexist = (1,2,3);
print("defined() The array \@iexist ");
defined @iexist ? print("exists.\n") : print("does not exist.\n");
Category named unary operator (hash) Arguments expression Return Value value
Use this function to delete an element from a hash array, given the key for the element to delete, returning the value of the deleted element.
%Hash = (1, One, 2, Two, 3, Three);
print("delete() Deleted ",delete($Hash{1}),"\n");
Category list operator (i/o) Arguments list Return Value errorlevel
This function terminates execution of the Perl script when called printing the value of the list argument to STDERR (as if called with print(STDERR, list)). The exit value is the current value of $OS_ERROR ($!), which may have been set by a previous function. If this has a value of zero it returns $CHILD_ERROR ($?). If this is zero, it exits with errorlevel 255. If the error message string specified by the list does not end in a newline, the text "at $PROGRAM_NAME at line line, where line is the line number of the Perl script.
die("die() Now we can give an example of die()...exiting");
Category (flow) Arguments block Arguments subroutine(list) Arguments expression Return Value special
This is a syntax structure that allows repeated execution of a block of statements. The value returned is the result of the last statement in the block. Normally an exit condition is supplied after the block. The second form where the argument is subroutine() is a depreciated form. The third form executes the contents of the file name specified by the expression (but it is better to use use() or require() instead, because this has better error checking).
$i=1;
print("do ");
$return = do {
print $i, " ";
$i++;
} until $i==3;
print("Returned $return\n");
Category named unary operator (misc) Arguments label Return Value N/A
This function causes the program to create a binary image core dump. This then allows the dumped image to be reloaded using the undump() function (if supported) which can effectively allow the use of precompiled Perl images. When reloaded, the program begins execution from the label specified. It is possible to set up a program which initializes data structures to dump() after the initialization so that execution is faster when reloading the dumped image.
Category named unary operator (hash) Arguments variable Return Value key, value
This function allows iteration over the elements in an associative array. Each time it is evaluated, it returns another list of two elements (a key, value pair from the associative array). When all the elements have been returned, it returns a null list.
%NumberWord = (1, One, 2, Two, 3, Three);
print("each() ");
while (($number,$wordform)=each(%NumberWord)) {
print("$number:$wordform ");
}
print("\n");
Category (system files) Arguments none Return Value 1 (true) '' (false)
This function closes the /etc/group file used by getgrent() and other group-related functions. It is equivalent to the UNIX system call.
($name,$pw,$gid,@members)=getgrent();
$returned = endgrent();
print("endgrent() Closes /etc/group [$name,$gid]",
" file returning $returned.\n");
Category (system files) Arguments none Return Value 1 (true) '' (false)
This function closes the TCP socket used by name server queries gethostbyname() and host- related functions. It is equivalent to the UNIX system call.
$host = gethostbyname("lynch");
$returned = endhostent();
print("endhostent() Closes /etc/hosts [$host]",
" returning $returned.\n");
Category (system files) Arguments none Return Value 1 (true) '' (false)
This function closes the /etc/networks file used by getnetent() and network-related functions. This function is equivalent to the UNIX system call.
($name,$alias,$net,$net) = getnetent();
$returned = endnetent();
print("endnetent() Closes /etc/networks [$name]",
" returning $returned.\n");
Category (system files) Arguments none Return Value 1 (true) '' (false)
This function closes the /etc/protocols file used by getprotoent() and protocol-related functions. It is equivalent to the UNIX system call.
($name, $alias, $protocol) = getprotoent();
$returned = endprotoent();
print("endprotoent() Closes /etc/protocols ",
"[$name,$alias,$protocol] file returning $returned.\n");
Category (system files) Arguments none Return Value 1 (true) '' (false)
This function closes the /etc/passwd file used by getpwent() and password-related functions. It is equivalent to the UNIX system call.
($name,$pass,$uid,$gid,$quota,$name,$gcos,$logindir,$shell) = getpwent();
$returned = endpwent();
print("endpwent() Closes /etc/passwd [$logindir,$shell] ",
"file returning $returned.\n");
Category (system files) Arguments none Return Value 1 (true) '' (false)
This function closes the /etc/servers file used by getservent() and related functions. It is equivalent to the UNIX system call.
($name,$aliases,$port,$protocol) = getservent();
$returned = endservent();
print("endservent() Closes /etc/servers [$name]",
" file returning $returned.\n");
Category named unary operator (i/o) Arguments handle Arguments () Arguments none Return Value 1 (true) '' (false)
This function tests if the file pointer to file specified by the file handle is at the end of the file. This is done by reading the next character and then undoing this operation (so is only suitable on files where this can be done safely). If no argument is supplied the file tested is the last file that was read. If the empty list is supplied then this tests if all the last files that supplied an argument to the Perl script are eof() (that is, it can be used as a termination condition in a while loop).
open INF, "/tmp/test1.txt";
if (eof INF)
{print "eof() TRUE\n";}
else
{print "eof() FALSE\n";}
close INF;
Category named unary operator (flow) Arguments expression Arguments block Arguments none Return Value special
This function treats the expression like a Perl program and executes
it by returning the return value of the last statement
executed. As the context of this execution is the same as that
of the script itself, variable definitions and subroutine definitions
persist. Syntax errors and runtime errors (including die())
are trapped and an undefined result is returned. If such an error
does occur, $EVAL_ERROR ($@) is set. If no errors are
found, $@ is equal to a defined null string. If no expression
is supplied, $_ is the default argument. If the block
syntax is used, the expressions in the block are evaluated only
once within the script, which may be more efficient for certain
situations.
| TIP |
eval() traps possible error conditions that would otherwise crash a program. Therefore, it can be used to test if certain features are available that would cause runtime errors if used when not available. |
$ans = 3;
eval "$ans = ;";
if ($@ eq "")
{print "eval() returned success.\n";}
else
{print "eval() error: $@";}
Category list operator (process) Arguments list Return Value N/A
This function passes control from the script to an external system command. There is no retain from this call so there is no return value. Note that system() calls external commands and does return to the next line in the calling Perl program.
This is equivalent to the UNIX system call execvp().
exec("cat /etc/motd");
Category named unary operator (hash) Arguments expression Return Value 1 (true) '' (false)
This function tests if a given key value exists in an associative array, returning a Boolean value.
%test = ( One, 1, Two, 2);
if (exists $test{One})
{print "exists() returned success.\n";}
else
{print "exists() returned an error.\n";}
Category named unary operator (flow) Arguments expression Arguments none Return Value value
This function evaluates the expression given as an argument and exits the program with that error. The default value for the error is 0 if no argument is supplied. Note that die() allows an error message.
exit(16);
Category named unary operator (numeric) Arguments expression Arguments none Return Value numeric
This function returns the natural log base (e) to the power of expression (or of $_ if none specified).
print "exp() e**1 is ",exp(1),"\n";
Category list operator (i/o) Arguments handle, function, packed_parameters
This function is equivalent to the UNIX fnctl() call. In Perl 5, use the fntcl module. In Perl 4, there should be some mechanism for linking the Perl functions to the system functions. This is usually executed when Perl is installed.
Category named unary operator (i/o) Arguments handle Return Value descriptor
This function returns the file descriptor given a file handle.
print("fileno() ",fileno(INF),"\n");
Category list operator (i/o) Arguments handle, operation Return Value 1 (true) '' (false)
This calls the UNIX flock() function to access file locks. The handle is a Perl file handle. The operation is any valid flock() operation: place exclusive lock, place shared lock, unlock. These operations are represented by numeric values.
Category (process) Arguments none Return Value pid
The fork function calls the UNIX fork() function or equivalent to fork a subprocess at this point. Returns the process ID (pid) of the child process to the calling process; returns 0 to the child process itself. The calling program should wait() on any child process it forks to avoid creating zombie processes.
$pid = fork;
# Child only prints this
if ($pid != 0) {
print("fork() Forking a process duplicates o/p: $pid \n");
}
waitpid($pid,0);
# Child exits here
if ($$ != $origpid) { die; }
Category: list operator (i/o) Arguments: format
This function declares an output format specification. These formats are used in conjunction with the write() function to control the output of variables and text to conform to a standard layout structure. Normally, the specification i