PERLAPIO(1) Perl Programmers Reference Guide PERLAPIO(1)

PERLAPIO(1) Perl Programmers Reference Guide PERLAPIO(1) #

PERLAPIO(1) Perl Programmers Reference Guide PERLAPIO(1)

NNAAMMEE #

 perlapio - perl's IO abstraction interface.

SSYYNNOOPPSSIISS #

   #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_fill(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);
   Size_t  PerlIO_unread(PerlIO *f,const void *vbuf, size_t count

   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, const char *mode);
   FILE   *PerlIO_findFILE(PerlIO *f);
   void    PerlIO_releaseFILE(PerlIO *f,FILE *stdio);

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

DDEESSCCRRIIPPTTIIOONN #

 Perl's source code, and extensions that want maximum portability, should
 use the above functions instead of those defined in ANSI C's _s_t_d_i_o_._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 _s_t_d_i_o_._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 two implementations:

1. USE_STDIO #

     All above are #define'd to stdio functions or are trivial wrapper
     functions which call stdio. In this case _o_n_l_y 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 _a_t _r_u_n _t_i_m_e. 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.

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

 PPeerrllIIOO__ooppeenn((ppaatthh,, mmooddee)), PPeerrllIIOO__ffddooppeenn((ffdd,,mmooddee))
     These correspond to ffooppeenn(())/ffddooppeenn(()) 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.

 PPeerrllIIOO__rreeooppeenn((ppaatthh,,mmooddee,,ff))
     While this currently exists in both implementations, perl itself does
     not use it. _A_s _p_e_r_l _d_o_e_s _n_o_t _u_s_e _i_t_, _i_t _i_s _n_o_t _w_e_l_l _t_e_s_t_e_d_.

     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.

 PPeerrllIIOO__pprriinnttff((ff,,ffmmtt,,......)), PPeerrllIIOO__vvpprriinnttff((ff,,ffmmtt,,aa))
     These are ffpprriinnttff(())/vvffpprriinnttff(()) equivalents.

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

 PPeerrllIIOO__rreeaadd((ff,,bbuuff,,ccoouunntt)), PPeerrllIIOO__wwrriittee((ff,,bbuuff,,ccoouunntt))
     These correspond functionally to ffrreeaadd(()) and ffwwrriittee(()) but the
     arguments and return values are different.  The PPeerrllIIOO__rreeaadd(()) and
     PPeerrllIIOO__wwrriittee(()) signatures have been modeled on the more sane low
     level rreeaadd(()) and wwrriittee(()) 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.

 PPeerrllIIOO__ffiillll((ff))
     Fills the buffer associated with "f" with data from the layer below.
     "PerlIO_read" calls this as part of its normal operation.  Returns 0
     upon success; -1 on failure.

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

 PPeerrllIIOO__ppuuttss((ff,,ss)), PPeerrllIIOO__ppuuttcc((ff,,cc))
     These correspond to ffppuuttss(()) and ffppuuttcc(()).  Note that arguments have
     been revised to have "file" first.

 PPeerrllIIOO__uunnggeettcc((ff,,cc))
     This corresponds to uunnggeettcc(()).  Note that arguments have been revised
     to have "file" first.  Arranges that next read operation will return
     the byte cc.  Despite the implied "character" in the name only values
     in the range 0..0xFF are defined. Returns the byte cc 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.

 PPeerrllIIOO__uunnrreeaadd((ff,,bbuuff,,ccoouunntt))
     This allows one to unget more than a single byte.  It effectively
     unshifts "count" bytes onto the beginning of the buffer "buf", so
     that the next read operation(s) will return them before anything else
     that was in the buffer.

     Returns the number of unread bytes.

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

 PPeerrllIIOO__eeooff((ff))
     This corresponds to ffeeooff(()).  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 PPeerrllIIOO__sseeeekk(()), or PPeerrllIIOO__rreewwiinndd(()).

 PPeerrllIIOO__eerrrroorr((ff))
     This corresponds to ffeerrrroorr(()).  Returns a true/false indication of
     whether there has been an IO error on the handle.

 PPeerrllIIOO__ffiilleennoo((ff))
     This corresponds to ffiilleennoo(()), 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.

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

 PPeerrllIIOO__fflluusshh((ff))
     This corresponds to fffflluusshh(()).  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.

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

 PPeerrllIIOO__tteellll((ff))
     This corresponds to fftteellll(()).  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 PPeerrllIIOO__sseeeekk(())).
     Return value is of type "Off_t" which is a perl Configure value which
     may not be same as stdio's "off_t".

 PPeerrllIIOO__ggeettppooss((ff,,pp)), PPeerrllIIOO__sseettppooss((ff,,pp))
     These correspond (loosely) to ffggeettppooss(()) and ffsseettppooss(()). 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
     PPeerrllIIOO__tteellll(()) and PPeerrllIIOO__sseeeekk(()).

 PPeerrllIIOO__rreewwiinndd((ff))
     This corresponds to rreewwiinndd(()). It is usually defined as being

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

 PPeerrllIIOO__ttmmppffiillee(())
     This corresponds to ttmmppffiillee(()), 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 PPeerrllIIOO__cclloossee(())
     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.

 PPeerrllIIOO__sseettlliinneebbuuff((ff))
     This corresponds to sseettlliinneebbuuff(()).  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 _o_n_l_y when "dumping";
     it has nothing to do with $| auto-flush.)

CCoo--eexxiisstteennccee wwiitthh ssttddiioo 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

 _b_e_f_o_r_e 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.

 PPeerrllIIOO__iimmppoorrttFFIILLEE((ff,,mmooddee))
     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 _O_N_L_Y 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 nnoott the reverse of PPeerrllIIOO__eexxppoorrttFFIILLEE(()).

 PPeerrllIIOO__eexxppoorrttFFIILLEE((ff,,mmooddee))
     Given a PerlIO * create a 'native' FILE * suitable for passing to
     code expecting to be compiled and linked with ANSI C _s_t_d_i_o_._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 PPeerrllIIOO__iimmppoorrttFFIILLEE(()) 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).

 PPeerrllIIOO__rreelleeaasseeFFIILLEE((pp,,ff))
     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 PPeerrllIIOO__eexxppoorrttFFIILLEE(()).

 PPeerrllIIOO__ffiinnddFFIILLEE((ff))
     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()".

“"FFaasstt ggeettss"” FFuunnccttiioonnss 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.

 PPeerrllIIOO__ffaasstt__ggeettss((ff))
     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'

 PPeerrllIIOO__hhaass__ccnnttppttrr((ff))
     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.

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

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

 PPeerrllIIOO__sseett__ppttrrccnntt((ff,,pp,,cc))
     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 _m_u_s_t be consistent with each other (implementation may only
     use one or the other or may require both).

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

 PPeerrllIIOO__sseett__ccnntt((ff,,cc))
     Obscure - set count of bytes in the buffer. Deprecated.  Only usable
     if PPeerrllIIOO__ccaannsseett__ccnntt(()) 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
     PPeerrllIIOO__sseett__ppttrrccnntt(()).

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

 PPeerrllIIOO__ggeett__bbaassee((ff))
     Return _s_t_a_r_t of buffer. Access only positive offsets in the buffer up
     to the value returned by PPeerrllIIOO__ggeett__bbuuffssiizz(()).

 PPeerrllIIOO__ggeett__bbuuffssiizz((ff))
     Return the _t_o_t_a_l _n_u_m_b_e_r _o_f _b_y_t_e_s 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.

OOtthheerr FFuunnccttiioonnss PerlIO_apply_layers(aTHX_ f,mode,layers) The new interface to the USE_PERLIO implementation. The layers “:crlf” and “:raw” are the only ones allowed for other implementations and those are silently ignored. (As of perl5.8 “:raw” is deprecated.) Use PPeerrllIIOO__bbiinnmmooddee(()) below for the portable case.

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

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

     iimmooddee is "O_BINARY" or "O_TEXT".

     llaayyeerrss 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(aTHX_ f,ptype,O_BINARY,NULL);
     and
         PerlIO_binmode(aTHX_ 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 pprriinnttff(())-like function which can be used for
     debugging.  No return value. Its main use is inside PerlIO where
     using real printf, wwaarrnn(()) 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, PPeerrllIIOO__ddeebbuugg(()) is a no-op.

perl v5.36.3 2023-02-15 PERLAPIO(1)