perlapio(1)


NAME

   perlapio - perl's IO abstraction interface.

SYNOPSIS

     #define PERLIO_NOT_STDIO 0    /* For co-existence with stdio only */
     #include <perlio.h>           /* Usually via #include <perl.h> */

     PerlIO *PerlIO_stdin(void);
     PerlIO *PerlIO_stdout(void);
     PerlIO *PerlIO_stderr(void);

     PerlIO *PerlIO_open(const char *path,const char *mode);
     PerlIO *PerlIO_fdopen(int fd, const char *mode);
     PerlIO *PerlIO_reopen(const char *path, /* deprecated */
             const char *mode, PerlIO *old);
     int     PerlIO_close(PerlIO *f);

     int     PerlIO_stdoutf(const char *fmt,...)
     int     PerlIO_puts(PerlIO *f,const char *string);
     int     PerlIO_putc(PerlIO *f,int ch);
     SSize_t PerlIO_write(PerlIO *f,const void *buf,size_t numbytes);
     int     PerlIO_printf(PerlIO *f, const char *fmt,...);
     int     PerlIO_vprintf(PerlIO *f, const char *fmt, va_list args);
     int     PerlIO_flush(PerlIO *f);

     int     PerlIO_eof(PerlIO *f);
     int     PerlIO_error(PerlIO *f);
     void    PerlIO_clearerr(PerlIO *f);

     int     PerlIO_getc(PerlIO *d);
     int     PerlIO_ungetc(PerlIO *f,int ch);
     SSize_t PerlIO_read(PerlIO *f, void *buf, size_t numbytes);

     int     PerlIO_fileno(PerlIO *f);

     void    PerlIO_setlinebuf(PerlIO *f);

     Off_t   PerlIO_tell(PerlIO *f);
     int     PerlIO_seek(PerlIO *f, Off_t offset, int whence);
     void    PerlIO_rewind(PerlIO *f);

     int     PerlIO_getpos(PerlIO *f, SV *save);    /* prototype changed */
     int     PerlIO_setpos(PerlIO *f, SV *saved);   /* prototype changed */

     int     PerlIO_fast_gets(PerlIO *f);
     int     PerlIO_has_cntptr(PerlIO *f);
     SSize_t PerlIO_get_cnt(PerlIO *f);
     char   *PerlIO_get_ptr(PerlIO *f);
     void    PerlIO_set_ptrcnt(PerlIO *f, char *ptr, SSize_t count);

     int     PerlIO_canset_cnt(PerlIO *f);              /* deprecated */
     void    PerlIO_set_cnt(PerlIO *f, int count);      /* deprecated */

     int     PerlIO_has_base(PerlIO *f);
     char   *PerlIO_get_base(PerlIO *f);
     SSize_t PerlIO_get_bufsiz(PerlIO *f);

     PerlIO *PerlIO_importFILE(FILE *stdio, const char *mode);
     FILE   *PerlIO_exportFILE(PerlIO *f, int flags);
     FILE   *PerlIO_findFILE(PerlIO *f);
     void    PerlIO_releaseFILE(PerlIO *f,FILE *stdio);

     int     PerlIO_apply_layers(PerlIO *f, const char *mode,
                                                       const char *layers);
     int     PerlIO_binmode(PerlIO *f, int ptype, int imode,
                                                       const char *layers);
     void    PerlIO_debug(const char *fmt,...)

DESCRIPTION

   Perl's source code, and extensions that want maximum portability,
   should use the above functions instead of those defined in ANSI C's
   stdio.h.  The perl headers (in particular "perlio.h") will "#define"
   them to the I/O mechanism selected at Configure time.

   The functions are modeled on those in stdio.h, but parameter order has
   been "tidied up a little".

   "PerlIO *" takes the place of FILE *. Like FILE * it should be treated
   as opaque (it is probably safe to assume it is a pointer to something).

   There are currently three implementations:

   1. USE_STDIO
       All above are #define'd to stdio functions or are trivial wrapper
       functions which call stdio. In this case only PerlIO * is a FILE *.
       This has been the default implementation since the abstraction was
       introduced in perl5.003_02.

   2. USE_PERLIO
       Introduced just after perl5.7.0, this is a re-implementation of the
       above abstraction which allows perl more control over how IO is
       done as it decouples IO from the way the operating system and C
       library choose to do things. For USE_PERLIO PerlIO * has an extra
       layer of indirection - it is a pointer-to-a-pointer.  This allows
       the PerlIO * to remain with a known value while swapping the
       implementation around underneath at run time. In this case all the
       above are true (but very simple) functions which call the
       underlying implementation.

       This is the only implementation for which "PerlIO_apply_layers()"
       does anything "interesting".

       The USE_PERLIO implementation is described in perliol.

   Because "perlio.h" is a thin layer (for efficiency) the semantics of
   these functions are somewhat dependent on the underlying
   implementation.  Where these variations are understood they are noted
   below.

   Unless otherwise noted, functions return 0 on success, or a negative
   value (usually "EOF" which is usually -1) and set "errno" on error.

   PerlIO_stdin(), PerlIO_stdout(), PerlIO_stderr()
       Use these rather than "stdin", "stdout", "stderr". They are written
       to look like "function calls" rather than variables because this
       makes it easier to make them function calls if platform cannot
       export data to loaded modules, or if (say) different "threads"
       might have different values.

   PerlIO_open(path, mode), PerlIO_fdopen(fd,mode)
       These correspond to fopen()/fdopen() and the arguments are the
       same.  Return "NULL" and set "errno" if there is an error.  There
       may be an implementation limit on the number of open handles, which
       may be lower than the limit on the number of open files - "errno"
       may not be set when "NULL" is returned if this limit is exceeded.

   PerlIO_reopen(path,mode,f)
       While this currently exists in all three implementations perl
       itself does not use it. As perl does not use it, it is not well
       tested.

       Perl prefers to "dup" the new low-level descriptor to the
       descriptor used by the existing PerlIO. This may become the
       behaviour of this function in the future.

   PerlIO_printf(f,fmt,...), PerlIO_vprintf(f,fmt,a)
       These are fprintf()/vfprintf() equivalents.

   PerlIO_stdoutf(fmt,...)
       This is printf() equivalent. printf is #defined to this function,
       so it is (currently) legal to use "printf(fmt,...)" in perl
       sources.

   PerlIO_read(f,buf,count), PerlIO_write(f,buf,count)
       These correspond functionally to fread() and fwrite() but the
       arguments and return values are different.  The PerlIO_read() and
       PerlIO_write() signatures have been modeled on the more sane low
       level read() and write() functions instead: The "file" argument is
       passed first, there is only one "count", and the return value can
       distinguish between error and "EOF".

       Returns a byte count if successful (which may be zero or positive),
       returns negative value and sets "errno" on error.  Depending on
       implementation "errno" may be "EINTR" if operation was interrupted
       by a signal.

   PerlIO_close(f)
       Depending on implementation "errno" may be "EINTR" if operation was
       interrupted by a signal.

   PerlIO_puts(f,s), PerlIO_putc(f,c)
       These correspond to fputs() and fputc().  Note that arguments have
       been revised to have "file" first.

   PerlIO_ungetc(f,c)
       This corresponds to ungetc().  Note that arguments have been
       revised to have "file" first.  Arranges that next read operation
       will return the byte c.  Despite the implied "character" in the
       name only values in the range 0..0xFF are defined. Returns the byte
       c on success or -1 ("EOF") on error.  The number of bytes that can
       be "pushed back" may vary, only 1 character is certain, and then
       only if it is the last character that was read from the handle.

   PerlIO_getc(f)
       This corresponds to getc().  Despite the c in the name only byte
       range 0..0xFF is supported.  Returns the character read or -1
       ("EOF") on error.

   PerlIO_eof(f)
       This corresponds to feof().  Returns a true/false indication of
       whether the handle is at end of file.  For terminal devices this
       may or may not be "sticky" depending on the implementation.  The
       flag is cleared by PerlIO_seek(), or PerlIO_rewind().

   PerlIO_error(f)
       This corresponds to ferror().  Returns a true/false indication of
       whether there has been an IO error on the handle.

   PerlIO_fileno(f)
       This corresponds to fileno(), note that on some platforms, the
       meaning of "fileno" may not match Unix. Returns -1 if the handle
       has no open descriptor associated with it.

   PerlIO_clearerr(f)
       This corresponds to clearerr(), i.e., clears 'error' and (usually)
       'eof' flags for the "stream". Does not return a value.

   PerlIO_flush(f)
       This corresponds to fflush().  Sends any buffered write data to the
       underlying file.  If called with "NULL" this may flush all open
       streams (or core dump with some USE_STDIO implementations).
       Calling on a handle open for read only, or on which last operation
       was a read of some kind may lead to undefined behaviour on some
       USE_STDIO implementations.  The USE_PERLIO (layers) implementation
       tries to behave better: it flushes all open streams when passed
       "NULL", and attempts to retain data on read streams either in the
       buffer or by seeking the handle to the current logical position.

   PerlIO_seek(f,offset,whence)
       This corresponds to fseek().  Sends buffered write data to the
       underlying file, or discards any buffered read data, then positions
       the file descriptor as specified by offset and whence (sic).  This
       is the correct thing to do when switching between read and write on
       the same handle (see issues with PerlIO_flush() above).  Offset is
       of type "Off_t" which is a perl Configure value which may not be
       same as stdio's "off_t".

   PerlIO_tell(f)
       This corresponds to ftell().  Returns the current file position, or
       (Off_t) -1 on error.  May just return value system "knows" without
       making a system call or checking the underlying file descriptor (so
       use on shared file descriptors is not safe without a
       PerlIO_seek()). Return value is of type "Off_t" which is a perl
       Configure value which may not be same as stdio's "off_t".

   PerlIO_getpos(f,p), PerlIO_setpos(f,p)
       These correspond (loosely) to fgetpos() and fsetpos(). Rather than
       stdio's Fpos_t they expect a "Perl Scalar Value" to be passed. What
       is stored there should be considered opaque. The layout of the data
       may vary from handle to handle.  When not using stdio or if
       platform does not have the stdio calls then they are implemented in
       terms of PerlIO_tell() and PerlIO_seek().

   PerlIO_rewind(f)
       This corresponds to rewind(). It is usually defined as being

           PerlIO_seek(f,(Off_t)0L, SEEK_SET);
           PerlIO_clearerr(f);

   PerlIO_tmpfile()
       This corresponds to tmpfile(), i.e., returns an anonymous PerlIO or
       NULL on error.  The system will attempt to automatically delete the
       file when closed.  On Unix the file is usually "unlink"-ed just
       after it is created so it does not matter how it gets closed. On
       other systems the file may only be deleted if closed via
       PerlIO_close() and/or the program exits via "exit".  Depending on
       the implementation there may be "race conditions" which allow other
       processes access to the file, though in general it will be safer in
       this regard than ad. hoc. schemes.

   PerlIO_setlinebuf(f)
       This corresponds to setlinebuf().  Does not return a value. What
       constitutes a "line" is implementation dependent but usually means
       that writing "\n" flushes the buffer.  What happens with things
       like "this\nthat" is uncertain.  (Perl core uses it only when
       "dumping"; it has nothing to do with $| auto-flush.)

   Co-existence with stdio
   There is outline support for co-existence of PerlIO with stdio.
   Obviously if PerlIO is implemented in terms of stdio there is no
   problem. However in other cases then mechanisms must exist to create a
   FILE * which can be passed to library code which is going to use stdio
   calls.

   The first step is to add this line:

      #define PERLIO_NOT_STDIO 0

   before including any perl header files. (This will probably become the
   default at some point).  That prevents "perlio.h" from attempting to
   #define stdio functions onto PerlIO functions.

   XS code is probably better using "typemap" if it expects FILE *
   arguments.  The standard typemap will be adjusted to comprehend any
   changes in this area.

   PerlIO_importFILE(f,mode)
       Used to get a PerlIO * from a FILE *.

       The mode argument should be a string as would be passed to
       fopen/PerlIO_open.  If it is NULL then - for legacy support - the
       code will (depending upon the platform and the implementation)
       either attempt to empirically determine the mode in which f is
       open, or use "r+" to indicate a read/write stream.

       Once called the FILE * should ONLY be closed by calling
       "PerlIO_close()" on the returned PerlIO *.

       The PerlIO is set to textmode. Use PerlIO_binmode if this is not
       the desired mode.

       This is not the reverse of PerlIO_exportFILE().

   PerlIO_exportFILE(f,mode)
       Given a PerlIO * create a 'native' FILE * suitable for passing to
       code expecting to be compiled and linked with ANSI C stdio.h.  The
       mode argument should be a string as would be passed to
       fopen/PerlIO_open.  If it is NULL then - for legacy support - the
       FILE * is opened in same mode as the PerlIO *.

       The fact that such a FILE * has been 'exported' is recorded,
       (normally by pushing a new :stdio "layer" onto the PerlIO *), which
       may affect future PerlIO operations on the original PerlIO *.  You
       should not call "fclose()" on the file unless you call
       "PerlIO_releaseFILE()" to disassociate it from the PerlIO *.  (Do
       not use PerlIO_importFILE() for doing the disassociation.)

       Calling this function repeatedly will create a FILE * on each call
       (and will push an :stdio layer each time as well).

   PerlIO_releaseFILE(p,f)
       Calling PerlIO_releaseFILE informs PerlIO that all use of FILE * is
       complete. It is removed from the list of 'exported' FILE *s, and
       the associated PerlIO * should revert to its original behaviour.

       Use this to disassociate a file from a PerlIO * that was associated
       using PerlIO_exportFILE().

   PerlIO_findFILE(f)
       Returns a native FILE * used by a stdio layer. If there is none, it
       will create one with PerlIO_exportFILE. In either case the FILE *
       should be considered as belonging to PerlIO subsystem and should
       only be closed by calling "PerlIO_close()".

   "Fast gets" Functions
   In addition to standard-like API defined so far above there is an
   "implementation" interface which allows perl to get at internals of
   PerlIO.  The following calls correspond to the various FILE_xxx macros
   determined by Configure - or their equivalent in other implementations.
   This section is really of interest to only those concerned with
   detailed perl-core behaviour, implementing a PerlIO mapping or writing
   code which can make use of the "read ahead" that has been done by the
   IO system in the same way perl does. Note that any code that uses these
   interfaces must be prepared to do things the traditional way if a
   handle does not support them.

   PerlIO_fast_gets(f)
       Returns true if implementation has all the interfaces required to
       allow perl's "sv_gets" to "bypass" normal IO mechanism.  This can
       vary from handle to handle.

         PerlIO_fast_gets(f) = PerlIO_has_cntptr(f) && \
                               PerlIO_canset_cnt(f) && \
                               'Can set pointer into buffer'

   PerlIO_has_cntptr(f)
       Implementation can return pointer to current position in the
       "buffer" and a count of bytes available in the buffer.  Do not use
       this - use PerlIO_fast_gets.

   PerlIO_get_cnt(f)
       Return count of readable bytes in the buffer. Zero or negative
       return means no more bytes available.

   PerlIO_get_ptr(f)
       Return pointer to next readable byte in buffer, accessing via the
       pointer (dereferencing) is only safe if PerlIO_get_cnt() has
       returned a positive value.  Only positive offsets up to value
       returned by PerlIO_get_cnt() are allowed.

   PerlIO_set_ptrcnt(f,p,c)
       Set pointer into buffer, and a count of bytes still in the buffer.
       Should be used only to set pointer to within range implied by
       previous calls to "PerlIO_get_ptr" and "PerlIO_get_cnt". The two
       values must be consistent with each other (implementation may only
       use one or the other or may require both).

   PerlIO_canset_cnt(f)
       Implementation can adjust its idea of number of bytes in the
       buffer.  Do not use this - use PerlIO_fast_gets.

   PerlIO_set_cnt(f,c)
       Obscure - set count of bytes in the buffer. Deprecated.  Only
       usable if PerlIO_canset_cnt() returns true.  Currently used in only
       doio.c to force count less than -1 to -1.  Perhaps should be
       PerlIO_set_empty or similar.  This call may actually do nothing if
       "count" is deduced from pointer and a "limit".  Do not use this -
       use PerlIO_set_ptrcnt().

   PerlIO_has_base(f)
       Returns true if implementation has a buffer, and can return pointer
       to whole buffer and its size. Used by perl for -T / -B tests.
       Other uses would be very obscure...

   PerlIO_get_base(f)
       Return start of buffer. Access only positive offsets in the buffer
       up to the value returned by PerlIO_get_bufsiz().

   PerlIO_get_bufsiz(f)
       Return the total number of bytes in the buffer, this is neither the
       number that can be read, nor the amount of memory allocated to the
       buffer. Rather it is what the operating system and/or
       implementation happened to "read()" (or whatever) last time IO was
       requested.

   Other Functions
   PerlIO_apply_layers(f,mode,layers)
       The new interface to the USE_PERLIO implementation. The layers
       ":crlf" and ":raw" are only ones allowed for other implementations
       and those are silently ignored. (As of perl5.8 ":raw" is
       deprecated.)  Use PerlIO_binmode() below for the portable case.

   PerlIO_binmode(f,ptype,imode,layers)
       The hook used by perl's "binmode" operator.  ptype is perl's
       character for the kind of IO:

       '<' read
       '>' write
       '+' read/write

       imode is "O_BINARY" or "O_TEXT".

       layers is a string of layers to apply, only ":crlf" makes sense in
       the non USE_PERLIO case. (As of perl5.8 ":raw" is deprecated in
       favour of passing NULL.)

       Portable cases are:

           PerlIO_binmode(f,ptype,O_BINARY,NULL);
       and
           PerlIO_binmode(f,ptype,O_TEXT,":crlf");

       On Unix these calls probably have no effect whatsoever.  Elsewhere
       they alter "\n" to CR,LF translation and possibly cause a special
       text "end of file" indicator to be written or honoured on read. The
       effect of making the call after doing any IO to the handle depends
       on the implementation. (It may be ignored, affect any data which is
       already buffered as well, or only apply to subsequent data.)

   PerlIO_debug(fmt,...)
       PerlIO_debug is a printf()-like function which can be used for
       debugging.  No return value. Its main use is inside PerlIO where
       using real printf, warn() etc. would recursively call PerlIO and be
       a problem.

       PerlIO_debug writes to the file named by $ENV{'PERLIO_DEBUG'} or
       defaults to stderr if the environment variable is not defined.
       Typical use might be

         Bourne shells (sh, ksh, bash, zsh, ash, ...):
          PERLIO_DEBUG=/tmp/perliodebug.log ./perl -Di somescript some args

         Csh/Tcsh:
          setenv PERLIO_DEBUG /tmp/perliodebug.log
          ./perl -Di somescript some args

         If you have the "env" utility:
          env PERLIO_DEBUG=/tmp/perliodebug.log ./perl -Di somescript args

         Win32:
          set PERLIO_DEBUG=perliodebug.log
          perl -Di somescript some args

       On a Perl built without "-DDEBUGGING", or when the "-Di" command-
       line switch is not specified, or under taint, PerlIO_debug() is a
       no-op.





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