1PERLAPIO(1) Perl Programmers Reference Guide PERLAPIO(1)
2
6 perlapio - perl's IO abstraction interface.
7
9 #define PERLIO_NOT_STDIO 0 /* For co-existence with stdio only */
10 #include <perlio.h> /* Usually via #include <perl.h> */
11 PerlIO *PerlIO_stdin(void);
13 PerlIO *PerlIO_stdout(void);
14 PerlIO *PerlIO_stderr(void);
15 PerlIO *PerlIO_open(const char *path,const char *mode);
17 PerlIO *PerlIO_fdopen(int fd, const char *mode);
18 PerlIO *PerlIO_reopen(const char *path, /* deprecated */
19 const char *mode, PerlIO *old);
20 int PerlIO_close(PerlIO *f);
21 int PerlIO_stdoutf(const char *fmt,...)
23 int PerlIO_puts(PerlIO *f,const char *string);
24 int PerlIO_putc(PerlIO *f,int ch);
25 SSize_t PerlIO_write(PerlIO *f,const void *buf,size_t numbytes);
26 int PerlIO_printf(PerlIO *f, const char *fmt,...);
27 int PerlIO_vprintf(PerlIO *f, const char *fmt, va_list args);
28 int PerlIO_flush(PerlIO *f);
29 int PerlIO_fill(PerlIO *f);
31 int PerlIO_eof(PerlIO *f);
32 int PerlIO_error(PerlIO *f);
33 void PerlIO_clearerr(PerlIO *f);
34 int PerlIO_getc(PerlIO *d);
36 int PerlIO_ungetc(PerlIO *f,int ch);
37 SSize_t PerlIO_read(PerlIO *f, void *buf, size_t numbytes);
38 Size_t PerlIO_unread(PerlIO *f,const void *vbuf, size_t count
39 int PerlIO_fileno(PerlIO *f);
41 void PerlIO_setlinebuf(PerlIO *f);
43 Off_t PerlIO_tell(PerlIO *f);
45 int PerlIO_seek(PerlIO *f, Off_t offset, int whence);
46 void PerlIO_rewind(PerlIO *f);
47 int PerlIO_getpos(PerlIO *f, SV *save); /* prototype changed */
49 int PerlIO_setpos(PerlIO *f, SV *saved); /* prototype changed */
50 int PerlIO_fast_gets(PerlIO *f);
52 int PerlIO_has_cntptr(PerlIO *f);
53 SSize_t PerlIO_get_cnt(PerlIO *f);
54 char *PerlIO_get_ptr(PerlIO *f);
55 void PerlIO_set_ptrcnt(PerlIO *f, char *ptr, SSize_t count);
56 int PerlIO_canset_cnt(PerlIO *f); /* deprecated */
58 void PerlIO_set_cnt(PerlIO *f, int count); /* deprecated */
59 int PerlIO_has_base(PerlIO *f);
61 char *PerlIO_get_base(PerlIO *f);
62 SSize_t PerlIO_get_bufsiz(PerlIO *f);
63 PerlIO *PerlIO_importFILE(FILE *stdio, const char *mode);
65 FILE *PerlIO_exportFILE(PerlIO *f, const char *mode);
66 FILE *PerlIO_findFILE(PerlIO *f);
67 void PerlIO_releaseFILE(PerlIO *f,FILE *stdio);
68 int PerlIO_apply_layers(pTHX_ PerlIO *f, const char *mode,
70 const char *layers);
71 int PerlIO_binmode(pTHX_ PerlIO *f, int ptype, int imode,
72 const char *layers);
73 void PerlIO_debug(const char *fmt,...);
74
76 Perl's source code, and extensions that want maximum portability,
77 should use the above functions instead of those defined in ANSI C's
78 stdio.h. The perl headers (in particular "perlio.h") will "#define"
79 them to the I/O mechanism selected at Configure time.
80 The functions are modeled on those in stdio.h, but parameter order has
82 been "tidied up a little".
83 "PerlIO *" takes the place of FILE *. Like FILE * it should be treated
85 as opaque (it is probably safe to assume it is a pointer to something).
86 There are currently two implementations:
88 1. USE_STDIO
90 All above are #define'd to stdio functions or are trivial wrapper
91 functions which call stdio. In this case only PerlIO * is a FILE *.
92 This has been the default implementation since the abstraction was
93 introduced in perl5.003_02.
94 2. USE_PERLIO
96 Introduced just after perl5.7.0, this is a re-implementation of the
97 above abstraction which allows perl more control over how IO is
98 done as it decouples IO from the way the operating system and C
99 library choose to do things. For USE_PERLIO PerlIO * has an extra
100 layer of indirection - it is a pointer-to-a-pointer. This allows
101 the PerlIO * to remain with a known value while swapping the
102 implementation around underneath at run time. In this case all the
103 above are true (but very simple) functions which call the
104 underlying implementation.
105 This is the only implementation for which "PerlIO_apply_layers()"
107 does anything "interesting".
108 The USE_PERLIO implementation is described in perliol.
110 Because "perlio.h" is a thin layer (for efficiency) the semantics of
112 these functions are somewhat dependent on the underlying
113 implementation. Where these variations are understood they are noted
114 below.
115 Unless otherwise noted, functions return 0 on success, or a negative
117 value (usually "EOF" which is usually -1) and set "errno" on error.
118 PerlIO_stdin(), PerlIO_stdout(), PerlIO_stderr()
120 Use these rather than "stdin", "stdout", "stderr". They are written
121 to look like "function calls" rather than variables because this
122 makes it easier to make them function calls if platform cannot
123 export data to loaded modules, or if (say) different "threads"
124 might have different values.
125 PerlIO_open(path, mode), PerlIO_fdopen(fd,mode)
127 These correspond to fopen()/fdopen() and the arguments are the
128 same. Return "NULL" and set "errno" if there is an error. There
129 may be an implementation limit on the number of open handles, which
130 may be lower than the limit on the number of open files - "errno"
131 may not be set when "NULL" is returned if this limit is exceeded.
132 PerlIO_reopen(path,mode,f)
134 While this currently exists in both implementations, perl itself
135 does not use it. As perl does not use it, it is not well tested.
136 Perl prefers to "dup" the new low-level descriptor to the
138 descriptor used by the existing PerlIO. This may become the
139 behaviour of this function in the future.
140 PerlIO_printf(f,fmt,...), PerlIO_vprintf(f,fmt,a)
142 These are fprintf()/vfprintf() equivalents.
143 PerlIO_stdoutf(fmt,...)
145 This is printf() equivalent. printf is #defined to this function,
146 so it is (currently) legal to use "printf(fmt,...)" in perl
147 sources.
148 PerlIO_read(f,buf,count), PerlIO_write(f,buf,count)
150 These correspond functionally to fread() and fwrite() but the
151 arguments and return values are different. The PerlIO_read() and
152 PerlIO_write() signatures have been modeled on the more sane low
153 level read() and write() functions instead: The "file" argument is
154 passed first, there is only one "count", and the return value can
155 distinguish between error and "EOF".
156 Returns a byte count if successful (which may be zero or positive),
158 returns negative value and sets "errno" on error. Depending on
159 implementation "errno" may be "EINTR" if operation was interrupted
160 by a signal.
161 PerlIO_fill(f)
163 Fills the buffer associated with "f" with data from the layer
164 below. "PerlIO_read" calls this as part of its normal operation.
165 Returns 0 upon success; -1 on failure.
166 PerlIO_close(f)
168 Depending on implementation "errno" may be "EINTR" if operation was
169 interrupted by a signal.
170 PerlIO_puts(f,s), PerlIO_putc(f,c)
172 These correspond to fputs() and fputc(). Note that arguments have
173 been revised to have "file" first.
174 PerlIO_ungetc(f,c)
176 This corresponds to ungetc(). Note that arguments have been
177 revised to have "file" first. Arranges that next read operation
178 will return the byte c. Despite the implied "character" in the
179 name only values in the range 0..0xFF are defined. Returns the byte
180 c on success or -1 ("EOF") on error. The number of bytes that can
181 be "pushed back" may vary, only 1 character is certain, and then
182 only if it is the last character that was read from the handle.
183 PerlIO_unread(f,buf,count)
185 This allows one to unget more than a single byte. It effectively
186 unshifts "count" bytes onto the beginning of the buffer "buf", so
187 that the next read operation(s) will return them before anything
188 else that was in the buffer.
189 Returns the number of unread bytes.
191 PerlIO_getc(f)
193 This corresponds to getc(). Despite the c in the name only byte
194 range 0..0xFF is supported. Returns the character read or -1
195 ("EOF") on error.
196 PerlIO_eof(f)
198 This corresponds to feof(). Returns a true/false indication of
199 whether the handle is at end of file. For terminal devices this
200 may or may not be "sticky" depending on the implementation. The
201 flag is cleared by PerlIO_seek(), or PerlIO_rewind().
202 PerlIO_error(f)
204 This corresponds to ferror(). Returns a true/false indication of
205 whether there has been an IO error on the handle.
206 PerlIO_fileno(f)
208 This corresponds to fileno(), note that on some platforms, the
209 meaning of "fileno" may not match Unix. Returns -1 if the handle
210 has no open descriptor associated with it.
211 PerlIO_clearerr(f)
213 This corresponds to clearerr(), i.e., clears 'error' and (usually)
214 'eof' flags for the "stream". Does not return a value.
215 PerlIO_flush(f)
217 This corresponds to fflush(). Sends any buffered write data to the
218 underlying file. If called with "NULL" this may flush all open
219 streams (or core dump with some USE_STDIO implementations).
220 Calling on a handle open for read only, or on which last operation
221 was a read of some kind may lead to undefined behaviour on some
222 USE_STDIO implementations. The USE_PERLIO (layers) implementation
223 tries to behave better: it flushes all open streams when passed
224 "NULL", and attempts to retain data on read streams either in the
225 buffer or by seeking the handle to the current logical position.
226 PerlIO_seek(f,offset,whence)
228 This corresponds to fseek(). Sends buffered write data to the
229 underlying file, or discards any buffered read data, then positions
230 the file descriptor as specified by offset and whence (sic). This
231 is the correct thing to do when switching between read and write on
232 the same handle (see issues with PerlIO_flush() above). Offset is
233 of type "Off_t" which is a perl Configure value which may not be
234 same as stdio's "off_t".
235 PerlIO_tell(f)
237 This corresponds to ftell(). Returns the current file position, or
238 (Off_t) -1 on error. May just return value system "knows" without
239 making a system call or checking the underlying file descriptor (so
240 use on shared file descriptors is not safe without a
241 PerlIO_seek()). Return value is of type "Off_t" which is a perl
242 Configure value which may not be same as stdio's "off_t".
243 PerlIO_getpos(f,p), PerlIO_setpos(f,p)
245 These correspond (loosely) to fgetpos() and fsetpos(). Rather than
246 stdio's Fpos_t they expect a "Perl Scalar Value" to be passed. What
247 is stored there should be considered opaque. The layout of the data
248 may vary from handle to handle. When not using stdio or if
249 platform does not have the stdio calls then they are implemented in
250 terms of PerlIO_tell() and PerlIO_seek().
251 PerlIO_rewind(f)
253 This corresponds to rewind(). It is usually defined as being
254 PerlIO_seek(f,(Off_t)0L, SEEK_SET);
256 PerlIO_clearerr(f);
257 PerlIO_tmpfile()
259 This corresponds to tmpfile(), i.e., returns an anonymous PerlIO or
260 NULL on error. The system will attempt to automatically delete the
261 file when closed. On Unix the file is usually "unlink"-ed just
262 after it is created so it does not matter how it gets closed. On
263 other systems the file may only be deleted if closed via
264 PerlIO_close() and/or the program exits via "exit". Depending on
265 the implementation there may be "race conditions" which allow other
266 processes access to the file, though in general it will be safer in
267 this regard than ad. hoc. schemes.
268 PerlIO_setlinebuf(f)
270 This corresponds to setlinebuf(). Does not return a value. What
271 constitutes a "line" is implementation dependent but usually means
272 that writing "\n" flushes the buffer. What happens with things
273 like "this\nthat" is uncertain. (Perl core uses it only when
274 "dumping"; it has nothing to do with $| auto-flush.)
275 Co-existence with stdio
277 There is outline support for co-existence of PerlIO with stdio.
278 Obviously if PerlIO is implemented in terms of stdio there is no
279 problem. However in other cases then mechanisms must exist to create a
280 FILE * which can be passed to library code which is going to use stdio
281 calls.
282 The first step is to add this line:
284 #define PERLIO_NOT_STDIO 0
286 before including any perl header files. (This will probably become the
288 default at some point). That prevents "perlio.h" from attempting to
289 #define stdio functions onto PerlIO functions.
290 XS code is probably better using "typemap" if it expects FILE *
292 arguments. The standard typemap will be adjusted to comprehend any
293 changes in this area.
294 PerlIO_importFILE(f,mode)
296 Used to get a PerlIO * from a FILE *.
297 The mode argument should be a string as would be passed to
299 fopen/PerlIO_open. If it is NULL then - for legacy support - the
300 code will (depending upon the platform and the implementation)
301 either attempt to empirically determine the mode in which f is
302 open, or use "r+" to indicate a read/write stream.
303 Once called the FILE * should ONLY be closed by calling
305 "PerlIO_close()" on the returned PerlIO *.
306 The PerlIO is set to textmode. Use PerlIO_binmode if this is not
308 the desired mode.
309 This is not the reverse of PerlIO_exportFILE().
311 PerlIO_exportFILE(f,mode)
313 Given a PerlIO * create a 'native' FILE * suitable for passing to
314 code expecting to be compiled and linked with ANSI C stdio.h. The
315 mode argument should be a string as would be passed to
316 fopen/PerlIO_open. If it is NULL then - for legacy support - the
317 FILE * is opened in same mode as the PerlIO *.
318 The fact that such a FILE * has been 'exported' is recorded,
320 (normally by pushing a new :stdio "layer" onto the PerlIO *), which
321 may affect future PerlIO operations on the original PerlIO *. You
322 should not call "fclose()" on the file unless you call
323 "PerlIO_releaseFILE()" to disassociate it from the PerlIO *. (Do
324 not use PerlIO_importFILE() for doing the disassociation.)
325 Calling this function repeatedly will create a FILE * on each call
327 (and will push an :stdio layer each time as well).
328 PerlIO_releaseFILE(p,f)
330 Calling PerlIO_releaseFILE informs PerlIO that all use of FILE * is
331 complete. It is removed from the list of 'exported' FILE *s, and
332 the associated PerlIO * should revert to its original behaviour.
333 Use this to disassociate a file from a PerlIO * that was associated
335 using PerlIO_exportFILE().
336 PerlIO_findFILE(f)
338 Returns a native FILE * used by a stdio layer. If there is none, it
339 will create one with PerlIO_exportFILE. In either case the FILE *
340 should be considered as belonging to PerlIO subsystem and should
341 only be closed by calling "PerlIO_close()".
342 "Fast gets" Functions
344 In addition to standard-like API defined so far above there is an
345 "implementation" interface which allows perl to get at internals of
346 PerlIO. The following calls correspond to the various FILE_xxx macros
347 determined by Configure - or their equivalent in other implementations.
348 This section is really of interest to only those concerned with
349 detailed perl-core behaviour, implementing a PerlIO mapping or writing
350 code which can make use of the "read ahead" that has been done by the
351 IO system in the same way perl does. Note that any code that uses these
352 interfaces must be prepared to do things the traditional way if a
353 handle does not support them.
354 PerlIO_fast_gets(f)
356 Returns true if implementation has all the interfaces required to
357 allow perl's "sv_gets" to "bypass" normal IO mechanism. This can
358 vary from handle to handle.
359 PerlIO_fast_gets(f) = PerlIO_has_cntptr(f) && \
361 PerlIO_canset_cnt(f) && \
362 'Can set pointer into buffer'
363 PerlIO_has_cntptr(f)
365 Implementation can return pointer to current position in the
366 "buffer" and a count of bytes available in the buffer. Do not use
367 this - use PerlIO_fast_gets.
368 PerlIO_get_cnt(f)
370 Return count of readable bytes in the buffer. Zero or negative
371 return means no more bytes available.
372 PerlIO_get_ptr(f)
374 Return pointer to next readable byte in buffer, accessing via the
375 pointer (dereferencing) is only safe if PerlIO_get_cnt() has
376 returned a positive value. Only positive offsets up to value
377 returned by PerlIO_get_cnt() are allowed.
378 PerlIO_set_ptrcnt(f,p,c)
380 Set pointer into buffer, and a count of bytes still in the buffer.
381 Should be used only to set pointer to within range implied by
382 previous calls to "PerlIO_get_ptr" and "PerlIO_get_cnt". The two
383 values must be consistent with each other (implementation may only
384 use one or the other or may require both).
385 PerlIO_canset_cnt(f)
387 Implementation can adjust its idea of number of bytes in the
388 buffer. Do not use this - use PerlIO_fast_gets.
389 PerlIO_set_cnt(f,c)
391 Obscure - set count of bytes in the buffer. Deprecated. Only
392 usable if PerlIO_canset_cnt() returns true. Currently used in only
393 doio.c to force count less than -1 to -1. Perhaps should be
394 PerlIO_set_empty or similar. This call may actually do nothing if
395 "count" is deduced from pointer and a "limit". Do not use this -
396 use PerlIO_set_ptrcnt().
397 PerlIO_has_base(f)
399 Returns true if implementation has a buffer, and can return pointer
400 to whole buffer and its size. Used by perl for -T / -B tests.
401 Other uses would be very obscure...
402 PerlIO_get_base(f)
404 Return start of buffer. Access only positive offsets in the buffer
405 up to the value returned by PerlIO_get_bufsiz().
406 PerlIO_get_bufsiz(f)
408 Return the total number of bytes in the buffer, this is neither the
409 number that can be read, nor the amount of memory allocated to the
410 buffer. Rather it is what the operating system and/or
411 implementation happened to "read()" (or whatever) last time IO was
412 requested.
413 Other Functions
415 PerlIO_apply_layers(aTHX_ f,mode,layers)
416 The new interface to the USE_PERLIO implementation. The layers
417 ":crlf" and ":raw" are the only ones allowed for other
418 implementations and those are silently ignored. (As of perl5.8
419 ":raw" is deprecated.) Use PerlIO_binmode() below for the portable
420 case.
421 PerlIO_binmode(aTHX_ f,ptype,imode,layers)
423 The hook used by perl's "binmode" operator. ptype is perl's
424 character for the kind of IO:
425 '<' read
427 '>' write
428 '+' read/write
429 imode is "O_BINARY" or "O_TEXT".
431 layers is a string of layers to apply; only ":crlf" makes sense in
433 the non-USE_PERLIO case. (As of perl5.8 ":raw" is deprecated in
434 favour of passing NULL.)
435 Portable cases are:
437 PerlIO_binmode(aTHX_ f,ptype,O_BINARY,NULL);
439 and
440 PerlIO_binmode(aTHX_ f,ptype,O_TEXT,":crlf");
441 On Unix these calls probably have no effect whatsoever. Elsewhere
443 they alter "\n" to CR,LF translation and possibly cause a special
444 text "end of file" indicator to be written or honoured on read. The
445 effect of making the call after doing any IO to the handle depends
446 on the implementation. (It may be ignored, affect any data which is
447 already buffered as well, or only apply to subsequent data.)
448 PerlIO_debug(fmt,...)
450 PerlIO_debug is a printf()-like function which can be used for
451 debugging. No return value. Its main use is inside PerlIO where
452 using real printf, warn() etc. would recursively call PerlIO and be
453 a problem.
454 PerlIO_debug writes to the file named by $ENV{'PERLIO_DEBUG'} or
456 defaults to stderr if the environment variable is not defined.
457 Typical use might be
458 Bourne shells (sh, ksh, bash, zsh, ash, ...):
460 PERLIO_DEBUG=/tmp/perliodebug.log ./perl -Di somescript some args
461 Csh/Tcsh:
463 setenv PERLIO_DEBUG /tmp/perliodebug.log
464 ./perl -Di somescript some args
465 If you have the "env" utility:
467 env PERLIO_DEBUG=/tmp/perliodebug.log ./perl -Di somescript args
468 Win32:
470 set PERLIO_DEBUG=perliodebug.log
471 perl -Di somescript some args
472 On a Perl built without "-DDEBUGGING", or when the "-Di" command-
474 line switch is not specified, or under taint, PerlIO_debug() is a
475 no-op.
476perl v5.36.0 2022-08-30 PERLAPIO(1)