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ERRATA

alarm(10);

$arcTangent = atan2(60,2);

open(FILE, "file.dat");
binmode(FILE);

$temp = { };
bless $temp, 'ATMPCLASS';
print("bless() \$temp is now has type ",
ref($temp), "\n");

Return Value in Scalar Context: SCALAR, true if the current code has been called as a subroutine (this includes code which is included using a require() or an eval() call). Otherwise, false.

Return Value in Array Context: ARRAY, contains details of the calling context comprising the package name, file name, and line of the call.

sub testcaller {
    ($package, $file, $line) = caller;
    print("caller() Package=$package
File=$file Line=$line\n");
}
testcaller();

chdir("/") ?
    print("It worked.\n") :
    print("It didn't work.\n");

chmod(0744, "test1.txt", "test2.txt");

$temp = "AAAAA!\n";
print("chomp(\$temp) returned ", chomp($temp), ".\n");

$tmp = "1234";
print("chop(\$tmp) returned ", chop($tmp), "\n");

chown(1, 1, "test1.txt");

chroot("/usr/~waters");

open(FILE, "test1.txt");
# some file activity
close(FILE);

opendir(DIR, ".");
# some directory activity
closedir(DIR);

$temp = cos(60);

$encyptedString = crypt("Password","TR");

Tip

This function has been superseded by the untie() function.

Tip

This function has been superseded by the tie() function.

@iexist = (1,2,3);
print("exists.\n") if defined(@iexist);
print("does not exist.\n") unless defined(@iexist);

%Hash = ('Jan' => 'One', 'Feb' => 'Two',
  'Mar' => 'Three');
delete($Hash{'Jan'});

die("Something fatal has happened and
  the script must die!");

%NumberWord = ('1' => 'One', '2' => 'Two',
  '3' => 'Three');
while (($key, $value) = each(%NumberWord)) {
    print("$key: $value\n");
}

($name, $pw, $gid, @members) = getgrent();
endgrent();

$host = gethostbyname("lynch");
endhostent();

($name, $aliases, $addrtype, $net) = getnetent();
endnetent();

($name, $alias, $protocol) = getprotoent();
endprotoent();

($name, $pass, $uid, $gid, $quota, $name,
    $gcos, $logindir, $shell) = getpwent();
endpwent();

($name, $aliases, $port, $protocol) = getservent();
endservent();

open(FILE, "test1.txt");
# some file activity
print("eof() returned ",
  eof(FILE) ? "TRUE" : "FALSE", "\n");
close(FILE);

Tip

eval() traps possible error conditions which would otherwise crash a program and so can be used to test if certain features are available which would cause runtime errors if used when not available. See Chapter 13, "Handling Errors and Signals," for more information.

$answer = 3;
eval("$answer = ;");
if ($@ eq "") {
    print("eval() returned success.\n");
}
else {
    print("eval() error: $@");
}

exec("cat /etc/motd");

%test = ( 'One' => '1', 'Two' => '2');
if (exists($test{'One'})) {
    print("exists() returned success.\n");
}
else {
    print("exists() returned an error.\n");
}

exit(16);

print "exp() e**1 is ", exp(1), "\n";

print("fileno() ", fileno(FILE), "\n");

open(FILE, "/etc/motd");
print "getc() ", getc(FILE), "\n";
close(FILE);

Return Value in Scalar Context : Returns the next group name. Or the undefined value if no more groups or an error occured.

Return Value in Array Context : ($name, $passwd, $gid, $members) or an empty list.

($name, $pw, $gid, @members) = getgrent();
print("getgrent() Examines
  /etc/group [$name,$gid] file.\n");

Return Value in Scalar Context: The next group name that belongs to GID.

Return Value in Array Context: ($name, $passwd, $gid, $members) or an empty list.

($grname, $grpw, $gid, @members) = getgrgid(0);
print("getgrgid() Returns group
  name given GID [$grname]\n");

Return Value in Scalar Context: The next group id that belongs to NAME.

Return Value in Array Context: ($name, $passwd, $gid, $members) or an empty list.

($grname, $grpw, $gid, @members) = getgrnam("root");
print("getgrnam() Returns group
  GID given name [$gid]\n");

Return Value in Scalar Context: Name of host addressed by ADDRESS. Or undefined if the host could not be found.

Return Value in Array Context: ($name, $aliases, $addrtype, $length, @addrs) or an empty list.

use Socket;
$addr = pack('C4', (140,203,7,103));
($name, $alias, $addrtype, $length, @addrs) =
gethostbyaddr($addr, AF_INET);
print("gethostbyaddr() [$alias].\n");

Return Value in Scalar Context: Address of the host called NAME. Or undefined if the host could not be found.

Return Value in Array Context: ($name, $aliases, $addrtype, $length, @addrs) or an empty list.

($name, $alias, $addrtype, $length, @addrs) =
   gethostbyname("lynch");
print("gethostbyname() [$alias].\n");

Return Value in Scalar Context: Name of the next host in /etc/hosts. or the undefined value.

Return Value in Array Context: ($name, $aliases, $addrtype, $length, @addrs) Or an empty list.

($name, $alias, $addrtype, $length, @addrs) =
   gethostent();
print("gethostent() [$alias].\n");

print ("getlogin() ", getlogin(), "\n");

Return Value in Scalar Context: The network name that has an address of ADDRESS or undefined.

Return Value in Array Context: ($name, $aliases, $addrtype, $net) or an empty list.

($addrtype) = (getnetent())[2];
($name, $alias, $addrtype, $net) =
  getnetbyaddr($net, $addrtype);
print("getnetbyaddr() Reads /etc/networks
  [$name]\n");

Return Value in Scalar Context: The network address of NAME or undefined.

Return Value in Array Context: ($name, $aliases, $addrtype, $net) or an empty list.

($name, $alias, $addrtype, $net) =
  getnetbyname("localnet");
print("getnetbyname() Reads /etc/networks
  [$name]\n");

Return Value in Scalar Context: The next network name in /etc/networks or undefined.

Return Value in Array Context: ($name, $aliases, $addrtype, $net) or an empty list.

($name, $alias, $addrtype, $net) =
  getnetent();
print("getnetent() Reads /etc/networks [$name,
  $addrtype]\n");

$sockaddr = 'S n a4 x8';
$packedRemoteAddr = getpeername(S);
($family, $port, $remoteAddr) =
   unpack($sockaddr,$packedRemoteAddr);

print("getpgrp() ", getpgrp(0), "\n");

print("getppid() ", getppid(), "\n");

print("getpriority() ", getpriority(0, 0), "\n");

Return Value in Scalar Context: The protocol number assigned to NAME.

Return Value in Array Context: ($name, $aliases, $proto) or an empty list. $proto is the protocol number.

($name, $alias, $proto) = getprotobyname("IP");
print("getprotobyname()
/etc/proto [$name, $alias, $proto].\n");

Return Value in Scalar Context: The protocol name associated with NUMBER.

Return Value in Array Context: ($name, $aliases, $proto) or an empty list.

($name, $alias, $proto) = getprotobynumber(0);
print("getprotobynumber()
/etc/protocols [$name, $alias, $proto].\n");

($name, $alias, $proto) = getprotoent();
print("getprotoent()
Closes /etc/protocols [$name, $alias, $proto].\n");

Return Value in Scalar Context: The username.

Return Value in Array Context: ARRAY. ($name, $passwd, $uid, $gid, $quota, $comment, $gcos, $dir, $shell) or an empty list.

($name, $pass, $uid, $gid,
$quota, $name, $gcos, $dir, $shell) = getpwent();
print("getpwent() /etc/passwd [$dir,
$shell].\n");

Return Value in Scalar Context: The userid of NAME.

Return Value in Array Context: ($name, $passwd, $uid, $gid, $quota, $comment, $gcos, $dir, $shell) or an empty list.

($name, $pass, $uid, $gid,
$quota, $name,
    $gcos, $dir, $shell) = getpwnam("root");
print("getpwnam() /etc/passwd [$dir,
$shell].\n");

Return Value in Scalar Context: The username of UID.

Return Value in Array Context: ($name, $passwd, $uid, $gid, $quota, $comment, $gcos, $dir, $shell) or an empty list.

($name, $pass, $uid, $gid,
$quota, $name,
    $gcos, $dir, $shell) = getpwuid(0);
print("getpwuid() /etc/passwd [$dir,
$shell].\n");

Return Value in Scalar Context: The port number.

Return Value in Array Context: ($name, $aliases, $port, $proto) or an empty list.

($name, $aliases, $port,
$protol) = getservbyname("tcpmux", "tcp");

Return Value in Scalar Context: The service name.

Return Value in Array Context: ($name, $aliases, $port, $proto) or an empty list.

($name, $aliases, $port,
$proto) = getservbyport(512, "tcp");

Return Value in Scalar Context: The next service name.

Return Value in Array Context: ($name, $aliases, $port, $proto) or an empty list.

($name, $aliases, $port,
$proto) = getservent();
print("getservent() /etc/servers
[$name].\n");

$packedAddr =
getsockname(S);
($family, $port, $localAddr) = unpack('S n a4 x8',
$packedAddr);

@files =
glob("*.txt");

Return Value in Scalar Context: A string like 'Sat Jul 13 07:34:46 1986' describing EXPR.

Return Value in Array Context: ($sec, $min, $hour, $mday, $mon, $year, $wday, $ydat, $isdst)

($sec, $min, $hour, $mday,
$mon, $year, $wday, $ydat, $isdst) = gmtime();
print "gmtime() 19$year-$mon-$mday\n";

Return Value in Scalar Context: The number of times that BLOCK or EXPR evaluated to true.

Return Value in Array Context: A list of the elements of LIST that cause BLOCK or EXPR to evaluate as true.

# Look for all elements that
begin with the letter T.
@a = ('One', 'Two', 'Three', 'Four', 'Five');
print("grep(), ", grep(/^T/, @a), "\n");

# Print all elements in a list.
@a = ('One', 'Two', 'Three', 'Four', 'Five');
grep( print("$_\n"), @a);

print("hex() ", hex("ff"),
"\n");

$answer1 =
index("abcdefghijiklmdef:-)", "def");
$answer2 = index("abcdefghijiklmdef", "def", $answer1 +
3);
print("index() def is at $answer1 and next at
$answer2\n");

print("int() ",
int(345.678), "\n");

@listone = (0, 1, 2, 3);
print("join() ", join("-",@listone), "\n");

Return Value in Scalar Context: The number of keys and, therefore, the number of entries in HASH.

Return Value in Array Context: All of the keys to HASH in no particular order.

%hash = ('One' => 1, 'Two'
=> 2, 'Three' => 3, 'Four' => 4);
print("keys() ", join("-", keys(%hash)),
"\n");

print("lc() ", lc("ABCDef"),
"\n");

print("lcfirst() ",
lcfirst("ABCDef"), "\n");

print("length() ",
length("01234"), "\n");

print("The result from
link() is ", link("/usr/local", "/tmp/link"), "\n");

local($numTires) =
10;

Return Value in Scalar Context: A string like 'Sat Jul 13 07:34:46 1986' describing EXPR.

Return Value in Array Context: ($sec, $min, $hour, $mday, $mon, $year, $wday, $ydat, $isdst)

($sec, $min, $hour, $mday,
$mon, $year, $wday, $ydat, $isdst) = localtime();
print("localtime() 19$year-$mon-$mday\n");

print("log() ", log(2.5),
"\n");

($device, $inode, $mode,
$nlink, $uid, $gid, $rdev, $size,
    $atime, $mtime, $ctime, $blksize, $blocks) =
lstat("/tmp/link");
print("lstat() $device, $inode, $ctime \n");

# Increment each element by
one.
@array = (0..3);
@result = map($_ + 1, @array);
print("Before map: @array\n");
print("After  map: @result\n");

# Print all elements in a list.
@array = ('One', 'Two', 'Three', 'Four', 'Five');
map( print("$_\n"), @array);

print("mkdir() ",
mkdir("testdir", 0777), "\n");

# Define the function foo
with four local variables.
sub foo {
    my($numTires) = shift;
    my(@params) = @_;
    my($tireType, $tirePressure);
}

print("oct() ", oct("88"),
"\n");

The file name string may be prefixed with the following values to indicate the mode:

Prefix Value	Description
<	read access, this is the default
>	write access
+>	create a file with read/write access
+<	read/write access to an existing file
>>	append to a file
" CMD |"	Execute CMD as an operating system command and pipe the resulting output back to your Perl script as FILEHANDLE.
"| CMD"	Pipe output to FILEHANDLE into CMD.

$FILE = "foo.dat"
open(FILE) or die("Unable to open $FILE because: $!");

$dir = "/tmp"
opendir(DIR, $dir) or
  die("Unable to open $dir because $!");

print("ord() ", ord('G'), "\n");

Format Specifier	Description
@	Null fill to absolute position.
A	Ascii string with spaces to pad.
a	Ascii string with nulls to pad.
b	Bit string (ascending bit order).
B	Bit string (descending bit order).
c	Signed char value.
C	Unsigned char value.
d	Double-precision float in the native format.
f	Single-precision float in the native format.
h	Hex string (low nybble first).
H	Hex string (high nybble first).
i	Signed integer value.
I	Unsigned integer value.
l	Signed long integer value.
L	Unsigned long integer value.
n	Short integer "network" order.
N	Long integer "network" order.
p	Pointer to a null-terminated string.
P	Pointer to a structure (fixed-length string).
s	Signed short integer value.
S	Unsigned short integer value.
u	UUencoded string.
v	Short integer "VAX" (little-endian) order.
V	Long integer "VAX" (little-endian) order.
x	Null byte.
X	Back up a byte.

A concise form of template can be used by appending a number after any letter to repeat that format specifier. For example, a5 indicates that five letters are expected. b32 indicates that 32 bits are expected. h8 indicates that 8 nybbles ( or 4 bytes) are expected. P10 indicates that the structure is 10 bytes long. Using a * in place of a number means to repeat the format specifier as necessary to use up all list values. Note that some packed structures may not be portable across machines (in particulat network and floating point formats). It should be possible to unpack the data using the same format specification with an unpack() call.

Use Socket;
@address = (140, 203, 7, 103)
$addr = pack('C4', @address);
print("@address is packed as: $addr\n");

@a = (1, 2, 3, 4);
print("pop() ", pop(@a), "leaves ",@a,
"\n");

$name = "alpha1 alpha2 alpha3 alpha4";
$name =~ m/alpha/g;
print("pos() ", pos($name), "\n");

# This example may look funny, but it works. Go ahead and
# try it!
#
    print(" returns ", print("print()"),
" on success.\n");
#
# The inside print() function is evaluated first,
# then the
# outer print() function is evaluated.

printf("printf() An integer printed with leading zeroes %05d.\n", 9);

# Find out how any elements are in @array.
# This works because
# you are essentially appending an empty array.
@array = ('A'..'R');
print("There are ", push(@array), "elements.\n");

@array = ( 1, 2 );
print("There are ", push(@array, (3, 4, 5)),
"elements.\n");

print(q(This is a single quoted string
  without interpolation), "\n");

print(qq(This is a double quoted string
  with interpolation\n));

print quotemeta("AB*\n[.]*");

@array = qw(This is a list of words without interpolation);

# summarize disk usage for the /tmp directory
# and store the output of the command into the
# @output array.
#
@output = qx(du -s /tmp);

# print a random number between 0 and 10.
print("rand(), ", rand(10), "\n");

sub readFile {
   my($buffer) = "";

   open(FILE, "/etc/services") or
     die("Error reading file, stopped");
   read(FILE, $buffer, 10);
   print("read() $buffer\n");
   close(CLOSE)
}

Return Value in Scalar Context: The name of the next file in the directory connected to DIRHANDLE.

Return Value in Array Context: A list containing all of the files in the directory connected to DIRHANDLE.

opendir(DIR, "/tmp");
@file = readdir(DIR);
print("readdir() @files\n");

$foobar = { };
bless($foobar, 'ATMPCLASS');
print("ref() \$foobar is now in class ", ref($foobar),
"\n";

print("rename() returned ",
  rename("/tmp/test", "/tmp/test2"), "\n");

reset('R');
reset('d-f');
reset();

Return Value in Scalar Context: A string with characters of the first element of LIST reversed.

Return Value in Array Context: The elements of LIST in reverse order.

@array = (1, 2, 3);
print("reverse() ", reverse(@array), "\n");

# Open the current directory
opendir(DIR, ".");

# Print all of the directory entries.
print("1st Time: ");
map( print("$_ ") , readdir(DIR));
print("\n");

# Print message verifying that there are
# no more directory entries to read.
print("The last file has already been read!\n\n")
 unless readdir(DIR);

# Go back to the beginning.
rewinddir(DIR);

# Print all of the directory entries again.
print("2nd Time: ");
map( print("$_ ") , readdir(DIR));
print("\n");

closedir(DIR);

$answer1 = rindex("abcdefghijiklmdef", "def");

# use the first position found as the offset to the
# next search.
# note that the length of the target string is
# subtracted from
# the offset to save time.
$answer2 = rindex("abcdefghijiklmdef", "def",
  $answer1 - 3);

print("rindex() \"def\" is at $answer1 and next
  at $answer2\n");

$numElements = scalar(@array);

open(FILE,">t.out");
    $oldHandle = select(FILE);
        print("This is sent to /tmp/t.out.\n");
    select($oldHandle);
print("This is sent to STDOUT.\n");

# Here is an advanced example which selects an alternate
# file handle and restores it in one step. The secret is
# the
# use of parentheses to create a list out of the return
# values
# of the statements evaluated by the comma operator.
open(FILE, ">t.out");
    select((select(FILE),
           print("This is sent to t.out.\n"))[0]);
print("This is sent to STDOUT.\n");

Return Value in Scalar Context: The number of ready descriptors that were found-usually referred to as $nfound.

Return Value in Array Context: ($nfound, $timeleft) - The number of ready descriptors and the amount of time left before a timeout happends.

sethostent(1);

setnetent(1);

print("setpriority() ", setpriority(0, 0, -20), "\n");

setprotoent(1);

setpwent();

setservent(1);

@array = (1..5);
while ($element = shift(@array)) {
    print("$element - ");
}
print("\n");

$temp = sin(4);

sleep(5);

Tip

When using socket(), make sure that you have the statement use Socket; at the top of your file so that the proper definitions get imported.

@array = ("z", "w", "r", "i", "b", "a");
print("sort() ", sort(@array), "\n");

# Replace the first three elements with capitalized
# versions.
@array        = ("a", "e", "i", "o", "u");
@removedItems =
   splice(@array, 0 , 3, ("A", "E", "I"));

Return Value in Scalar Context: Not recommended, but it returns the number of fields found and stored the fields in the @_ array.

Return Value in Array Context: A list of fields found in EXPR or $_ if no expression is specified.

@fields = split(/:/, "1:2:3:4:5");

$text = sprintf("%0d \n", 9);

$result = sqrt(4);

Tip

It is possible to generate exactly the same data repeatedly (without having to save the entire sequence) simply by stetting and saving the seed. Restoring the seed and calling rand() will then produce the same sequence again. srand(26); print("Here's a random number: ", rand(), ".\n"); srand(26); print("Here's the same random number: ", rand(), ".\n");

($device, $inode, $mode, $nlink, $uid, $gid, $rdev, $size,
    $atime, $mtime, $ctime, $blksize, $blocks) =
      stat("/etc/passwd");

print("stat() $device, $inode, $ctime\n");

$temp = substring("okay", 2);

Definition Creates a symbolic link from the existing file to the new file.

symlink("/usr/local", "/tmp/symlink_to_usr_local");

The first element in the list used as an argument to syscall() itself is the name corresponding to the UNIX system call (i.e. with the "SYS_" prefix). The next elements in the list are interpreted as parameters to this call. Numeric values are passed as the C type int. String values are passed as pointers to arrays. The length of these strings must be able to cope with any value assigned to that parameter in the call.

require(""syscall.ph");
syscall(&SYS_getpid);

Caution

This function, along with syswrite(), bypasses the standard low-level input/output functions that other Perl functions use. Therefore, sysread() and syswrite() should be mixed with other types of input and output functions.

Note

To capture the output from a system call use a back-quoted string instead of system().

system("ls -F /var > /tmp/t.tmp");

$filePos = tell(FILE);

opendir(DIR, "/tmp");
readdir(DIR);
print("telldir() ", telldir(DIR), "\n");

The behavior depends on the way the package class is written, and on the type of variable. Most common are package classes written to support associative arrays. In particular, package classes exist to bind associative arrays to various databases.

The tie() mechanism has the effect of hiding all the complexities of implementation behind a simple interface. For example, the records in a database can be accessed by looking at the associative array bound to the database.

The example here uses the Configure.pm module. This module stores the information about the machine on which Perl has been installed. It is possible to bind an associateive array to this class and examine this to find out the value of any of the configuration parameters.

use Configure;
$return = tie %c, Configure;
print("tie() returned \"$return\" and a sample
  value is $c{installbin}\n");

$then = time(); # time passes while code is running. $now = time(); $elaspedTime = $now - $then;

($usertime, $systemtime, $childsystem,
  $childuser) = times();
print("times() $usertime $systemtime $childsystem
  $childuser\n");

print("uc() ", uc("abcdEF"), "\n");

print("ucfirst() ", ucfirst("abcdEF"), "\n");

print("umask() The current umask is: ", umask(), "\n");

unlink("/tmp/t.tst", "/tmp/t.bak");

Return Value in Scalar Context: The first item unpacked from EXPR.

Return Value in Array Context: A list of element produced from EXPR.

@array = qw(a, b, c);
print("unshift() Array has ",
    unshift(@array, 1, 2, 3), " elements: @array\n");

utime(time(), time(), "/tmp/t.tst");

Return Value in Scalar Context: The number of values and, therefore, the number of entries in HASH.

Return Value in Array Context: All of the values in HASH in no particular order.

%hash = ('One' => 1, 'Two' => 2,
  'Three' => 3, 'Four' => 4);
print("keys() ", join("-", values(%hash)), "\n");

$vec = '';
vec($vec,  3, 4) = 1;  # bits 0 to 3
vec($vec,  7, 4) = 10; # bits 4 to 7
vec($vec, 11, 4) = 3;  # bits 8 to 11
vec($vec, 15, 4) = 15; # bits 12 to 15
# As there are 4 bits per number this can
# be decoded by unpack() as a hex number
print("vec() Has a created a string of nybbles,
    in hex: ", unpack("h*", $vec), "\n");

sub foo {
    return(wantarray() ? qw(A, B, C) : '1');
}

$result = foo();    # scalar context
@result = foo();    # array context

print("foo() in a  scalar context: $result\n");
print("foo() in an array  context:
@result\n");

warn("Unable to calculate value, using defaults instead.\n");

A format for use by that file handle must have been declared using a format statement. This defaults to the name of the file handle being used, but other format names can be associated with the current write() operation by using the $~ special variable.