MirOS Manual: perlapio(1)


PERLAPIO(1)     Perl Programmers Reference Guide      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, const char *mode, PerlIO *old);  /* deprecated */
         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);
         int     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);
         int     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);
         int     PerlIO_get_cnt(PerlIO *f);
         char   *PerlIO_get_ptr(PerlIO *f);
         void    PerlIO_set_ptrcnt(PerlIO *f, char *ptr, int count);

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

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         int     PerlIO_has_base(PerlIO *f);
         char   *PerlIO_get_base(PerlIO *f);
         int     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 porta-
     bility, should use the above functions instead of those
     defined in ANSI C's stdio.h.  The perl headers (in particu-
     lar "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_SFIO
         A "legacy" implementation in terms of the "sfio"
         library. Used for some specialist applications on Unix
         machines ("sfio" is not widely ported away from Unix).
         Most of above are #define'd to the sfio functions. Per-
         lIO * is in this case Sfio_t *.

     3. 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

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         time. In this case all the above are true (but very sim-
         ple) 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 under-
     stood 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 dif-
         ferent 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()

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         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 dis-
         tinguish 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 argu-
         ments 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 char-
         acter read or -1 ("EOF") on error.

     PerlIO_eof(f)
         This corresponds to feof().  Returns a true/false indi-
         cation of whether the handle is at end of file.  For
         terminal devices this may or may not be "sticky" depend-
         ing 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 plat-
         forms, the meaning of "fileno" may not match Unix.
         Returns -1 if the handle has no open descriptor

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         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 con-
         sidered 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

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             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 con-
         ditions" 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 func-
     tions.

     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

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         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 Per-
         lIO *.  (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

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     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, access-
         ing 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

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

         On Unix these calls probably have no effect whatsoever.

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         Elsewhere they alter "\n" to CR,LF translation and pos-
         sibly 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 sub-
         sequent 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'} typical use might be

           Bourne shells (sh, ksh, bash, zsh, ash, ...):
            PERLIO_DEBUG=/dev/tty ./perl somescript some args

           Csh/Tcsh:
            setenv PERLIO_DEBUG /dev/tty
            ./perl somescript some args

           If you have the "env" utility:
            env PERLIO_DEBUG=/dev/tty ./perl somescript some args

           Win32:
            set PERLIO_DEBUG=CON
            perl somescript some args

         If $ENV{'PERLIO_DEBUG'} is not set PerlIO_debug() is a
         no-op.

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