binmode, close, closedir, dbmclose, dbmopen, die, eof,
fileno, flock, format, getc, print, printf, read, readdir,
-rewinddir, seek, seekdir, select, syscall, sysread,
+rewinddir, seek, seekdir, select, syscall, sysread, sysseek,
syswrite, tell, telldir, truncate, warn, write
=item Functions for fixed length data or records
$hasargs, $wantarray, $evaltext, $is_require) = caller($i);
Here $subroutine may be C<"(eval)"> if the frame is not a subroutine
-call, but C<L<eval>>. In such a case additional elements $evaltext and
-$is_require are set: $is_require is true if the frame is created by
-C<L<require>> or C<L<use>> statement, $evaltext contains the text of
-C<L<eval EXPR>> statement. In particular, for C<L<eval BLOCK>>
-statement $filename is C<"(eval)">, but $evaltext is undefined. (Note
-also that C<L<use>> statement creates a C<L<require>> frame inside
-an C<L<eval EXPR>>) frame.
+call, but an C<eval>. In such a case additional elements $evaltext and
+$is_require are set: $is_require is true if the frame is created by a
+C<require> or C<use> statement, $evaltext contains the text of the
+C<eval EXPR> statement. In particular, for a C<eval BLOCK> statement,
+$filename is C<"(eval)">, but $evaltext is undefined. (Note also that
+each C<use> statement creates a C<require> frame inside an C<eval EXPR>)
+frame.
Furthermore, when called from within the DB package, caller returns more
detailed information: it sets the list variable @DB::args to be the
list must be the numerical mode, which should probably be an octal
number, and which definitely should I<not> a string of octal digits:
C<0644> is okay, C<'0644'> is not. Returns the number of files
-successfully changed. See also L<oct>, if all you have is a string.
+successfully changed. See also L</oct>, if all you have is a string.
$cnt = chmod 0755, 'foo', 'bar';
chmod 0755, @executables;
=item chr
Returns the character represented by that NUMBER in the character set.
-For example, C<chr(65)> is "A" in ASCII. For the reverse, use L<ord>.
+For example, C<chr(65)> is "A" in ASCII. For the reverse, use L</ord>.
If NUMBER is omitted, uses $_.
avoided.
When used on a hash element, it tells you whether the value is defined,
-not whether the key exists in the hash. Use L<exists> for the latter
+not whether the key exists in the hash. Use L</exists> for the latter
purpose.
Examples:
This counterintuitive behaviour of defined() on aggregates may be
changed, fixed, or broken in a future release of Perl.
-See also L<undef>, L<exists>, L<ref>.
+See also L</undef>, L</exists>, L</ref>.
=item delete EXPR
See L<perlform> for many details and examples.
-=item formline PICTURE, LIST
+=item formline PICTURE,LIST
This is an internal function used by C<format>s, though you may call it
too. It formats (see L<perlform>) a list of values according to the
Interprets EXPR as a hex string and returns the corresponding
value. (To convert strings that might start with either 0 or 0x
-see L<oct>.) If EXPR is omitted, uses $_.
+see L</oct>.) If EXPR is omitted, uses $_.
print hex '0xAf'; # prints '175'
print hex 'aF'; # same
=item ord
Returns the numeric ascii value of the first character of EXPR. If
-EXPR is omitted, uses $_. For the reverse, see L<chr>.
+EXPR is omitted, uses $_. For the reverse, see L</chr>.
=item pack TEMPLATE,LIST
c A signed char value.
C An unsigned char value.
+
s A signed short value.
S An unsigned short value.
+ (This 'short' is _exactly_ 16 bits, which may differ from
+ what a local C compiler calls 'short'.)
+
i A signed integer value.
I An unsigned integer value.
+ (This 'integer' is _at_least_ 32 bits wide. Its exact size
+ depends on what a local C compiler calls 'int', and may
+ even be larger than the 'long' described in the next item.)
+
l A signed long value.
L An unsigned long value.
+ (This 'long' is _exactly_ 32 bits, which may differ from
+ what a local C compiler calls 'long'.)
- n A short in "network" order.
- N A long in "network" order.
+ n A short in "network" (big-endian) order.
+ N A long in "network" (big-endian) order.
v A short in "VAX" (little-endian) order.
V A long in "VAX" (little-endian) order.
+ (These 'shorts' and 'longs' are _exactly_ 16 bits and
+ _exactly_ 32 bits, respectively.)
f A single-precision float in the native format.
d A double-precision float in the native format.
u A uuencoded string.
- w A BER compressed integer. Bytes give an unsigned integer base
- 128, most significant digit first, with as few digits as
- possible, and with the bit 8 of each byte except the last set
- to "1."
+ w A BER compressed integer. Its bytes represent an unsigned
+ integer in base 128, most significant digit first, with as few
+ digits as possible. Bit eight (the high bit) is set on each
+ byte except the last.
x A null byte.
X Back up a byte.
=item seek FILEHANDLE,POSITION,WHENCE
-Randomly positions the file pointer for FILEHANDLE, just like the fseek()
-call of stdio. FILEHANDLE may be an expression whose value gives the name
-of the filehandle. The values for WHENCE are 0 to set the file pointer to
-POSITION, 1 to set the it to current plus POSITION, and 2 to set it to EOF
-plus offset. You may use the values SEEK_SET, SEEK_CUR, and SEEK_END for
-this from the POSIX module. Returns 1 upon success, 0 otherwise.
+Sets FILEHANDLE's position, just like the fseek() call of stdio.
+FILEHANDLE may be an expression whose value gives the name of the
+filehandle. The values for WHENCE are 0 to set the new position to
+POSITION, 1 to set it to the current position plus POSITION, and 2 to
+set it to EOF plus POSITION (typically negative). For WHENCE you may
+use the constants SEEK_SET, SEEK_CUR, and SEEK_END from either the
+IO::Seekable or the POSIX module. Returns 1 upon success, 0 otherwise.
+
+If you want to position file for sysread() or syswrite(), don't use
+seek() -- buffering makes its effect on the file's system position
+unpredictable and non-portable. Use sysseek() instead.
On some systems you have to do a seek whenever you switch between reading
and writing. Amongst other things, this may have the effect of calling
-stdio's clearerr(3). A "whence" of 1 (SEEK_CUR) is useful for not moving
-the file pointer:
+stdio's clearerr(3). A WHENCE of 1 (SEEK_CUR) is useful for not moving
+the file position:
seek(TEST,0,1);
This is also useful for applications emulating C<tail -f>. Once you hit
EOF on your read, and then sleep for a while, you might have to stick in a
-seek() to reset things. First the simple trick listed above to clear the
-filepointer. The seek() doesn't change the current position, but it
-I<does> clear the end-of-file condition on the handle, so that the next
-C<E<lt>FILEE<gt>> makes Perl try again to read something. We hope.
+seek() to reset things. The seek() doesn't change the current position,
+but it I<does> clear the end-of-file condition on the handle, so that the
+next C<E<lt>FILEE<gt>> makes Perl try again to read something. We hope.
If that doesn't work (some stdios are particularly cantankerous), then
you may need something more like this:
=item sysread FILEHANDLE,SCALAR,LENGTH
Attempts to read LENGTH bytes of data into variable SCALAR from the
-specified FILEHANDLE, using the system call read(2). It bypasses
-stdio, so mixing this with other kinds of reads may cause confusion.
-Returns the number of bytes actually read, or undef if there was an
-error. SCALAR will be grown or shrunk so that the last byte actually
-read is the last byte of the scalar after the read.
+specified FILEHANDLE, using the system call read(2). It bypasses stdio,
+so mixing this with other kinds of reads, print(), write(), seek(), or
+tell() can cause confusion. Returns the number of bytes actually read,
+or undef if there was an error. SCALAR will be grown or shrunk so that
+the last byte actually read is the last byte of the scalar after the
+read.
An OFFSET may be specified to place the read data at some place in the
string other than the beginning. A negative OFFSET specifies
in the string being padded to the required size with "\0" bytes before
the result of the read is appended.
+=item sysseek FILEHANDLE,POSITION,WHENCE
+
+Sets FILEHANDLE's system position using the system call lseek(2). It
+bypasses stdio, so mixing this with reads (other than sysread()),
+print(), write(), seek(), or tell() may cause confusion. FILEHANDLE may
+be an expression whose value gives the name of the filehandle. The
+values for WHENCE are 0 to set the new position to POSITION, 1 to set
+the it to the current position plus POSITION, and 2 to set it to EOF
+plus POSITION (typically negative). For WHENCE, you may use the
+constants SEEK_SET, SEEK_CUR, and SEEK_END from either the IO::Seekable
+or the POSIX module.
+
+Returns the new position, or the undefined value on failure. A position
+of zero is returned as the string "0 but true"; thus sysseek() returns
+TRUE on success and FALSE on failure, yet you can still easily determine
+the new position.
+
=item system LIST
Does exactly the same thing as "exec LIST" except that a fork is done
Attempts to write LENGTH bytes of data from variable SCALAR to the
specified FILEHANDLE, using the system call write(2). It bypasses
-stdio, so mixing this with prints may cause confusion. Returns the
-number of bytes actually written, or undef if there was an error.
-If the length is greater than the available data, only as much data as
-is available will be written.
+stdio, so mixing this with reads (other than sysread()), print(),
+write(), seek(), or tell() may cause confusion. Returns the number of
+bytes actually written, or undef if there was an error. If the length
+is greater than the available data, only as much data as is available
+will be written.
An OFFSET may be specified to write the data from some part of the
string other than the beginning. A negative OFFSET specifies writing
=item tell
-Returns the current file position for FILEHANDLE. FILEHANDLE may be an
+Returns the current position for FILEHANDLE. FILEHANDLE may be an
expression whose value gives the name of the actual filehandle. If
FILEHANDLE is omitted, assumes the file last read.
Sets the umask for the process to EXPR and returns the previous value.
If EXPR is omitted, merely returns the current umask. Remember that a
umask is a number, usually given in octal; it is I<not> a string of octal
-digits. See also L<oct>, if all you have is a string.
+digits. See also L</oct>, if all you have is a string.
=item undef EXPR
=item write
-Writes a formatted record (possibly multiline) to the specified file,
+Writes a formatted record (possibly multi-line) to the specified file,
using the format associated with that file. By default the format for
a file is the one having the same name as the filehandle, but the
format for the current output channel (see the select() function) may be set
projects / p5sagit/p5-mst-13.2.git / blobdiff