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129 | .\" ======================================================================== | |
130 | .\" | |
131 | .IX Title "diagnostics 3" | |
132 | .TH diagnostics 3 "2002-06-01" "perl v5.8.0" "Perl Programmers Reference Guide" | |
133 | .SH "NAME" | |
134 | diagnostics \- Perl compiler pragma to force verbose warning diagnostics | |
135 | .PP | |
136 | splain \- standalone program to do the same thing | |
137 | .SH "SYNOPSIS" | |
138 | .IX Header "SYNOPSIS" | |
139 | As a pragma: | |
140 | .PP | |
141 | .Vb 2 | |
142 | \& use diagnostics; | |
143 | \& use diagnostics -verbose; | |
144 | .Ve | |
145 | .PP | |
146 | .Vb 2 | |
147 | \& enable diagnostics; | |
148 | \& disable diagnostics; | |
149 | .Ve | |
150 | .PP | |
151 | Aa a program: | |
152 | .PP | |
153 | .Vb 2 | |
154 | \& perl program 2>diag.out | |
155 | \& splain [-v] [-p] diag.out | |
156 | .Ve | |
157 | .SH "DESCRIPTION" | |
158 | .IX Header "DESCRIPTION" | |
159 | .ie n .Sh "The ""diagnostics"" Pragma" | |
160 | .el .Sh "The \f(CWdiagnostics\fP Pragma" | |
161 | .IX Subsection "The diagnostics Pragma" | |
162 | This module extends the terse diagnostics normally emitted by both the | |
163 | perl compiler and the perl interpreter, augmenting them with the more | |
164 | explicative and endearing descriptions found in perldiag. Like the | |
165 | other pragmata, it affects the compilation phase of your program rather | |
166 | than merely the execution phase. | |
167 | .PP | |
168 | To use in your program as a pragma, merely invoke | |
169 | .PP | |
170 | .Vb 1 | |
171 | \& use diagnostics; | |
172 | .Ve | |
173 | .PP | |
174 | at the start (or near the start) of your program. (Note | |
175 | that this \fIdoes\fR enable perl's \fB\-w\fR flag.) Your whole | |
176 | compilation will then be subject(ed :\-) to the enhanced diagnostics. | |
177 | These still go out \fB\s-1STDERR\s0\fR. | |
178 | .PP | |
179 | Due to the interaction between runtime and compiletime issues, | |
180 | and because it's probably not a very good idea anyway, | |
181 | you may not use \f(CW\*(C`no diagnostics\*(C'\fR to turn them off at compiletime. | |
182 | However, you may control their behaviour at runtime using the | |
183 | \&\fIdisable()\fR and \fIenable()\fR methods to turn them off and on respectively. | |
184 | .PP | |
185 | The \fB\-verbose\fR flag first prints out the perldiag introduction before | |
186 | any other diagnostics. The \f(CW$diagnostics::PRETTY\fR variable can generate nicer | |
187 | escape sequences for pagers. | |
188 | .PP | |
189 | Warnings dispatched from perl itself (or more accurately, those that match | |
190 | descriptions found in perldiag) are only displayed once (no duplicate | |
191 | descriptions). User code generated warnings ala \fIwarn()\fR are unaffected, | |
192 | allowing duplicate user messages to be displayed. | |
193 | .Sh "The \fIsplain\fP Program" | |
194 | .IX Subsection "The splain Program" | |
195 | While apparently a whole nuther program, \fIsplain\fR is actually nothing | |
196 | more than a link to the (executable) \fIdiagnostics.pm\fR module, as well as | |
197 | a link to the \fIdiagnostics.pod\fR documentation. The \fB\-v\fR flag is like | |
198 | the \f(CW\*(C`use diagnostics \-verbose\*(C'\fR directive. | |
199 | The \fB\-p\fR flag is like the | |
200 | \&\f(CW$diagnostics::PRETTY\fR variable. Since you're post-processing with | |
201 | \&\fIsplain\fR, there's no sense in being able to \fIenable()\fR or \fIdisable()\fR processing. | |
202 | .PP | |
203 | Output from \fIsplain\fR is directed to \fB\s-1STDOUT\s0\fR, unlike the pragma. | |
204 | .SH "EXAMPLES" | |
205 | .IX Header "EXAMPLES" | |
206 | The following file is certain to trigger a few errors at both | |
207 | runtime and compiletime: | |
208 | .PP | |
209 | .Vb 8 | |
210 | \& use diagnostics; | |
211 | \& print NOWHERE "nothing\en"; | |
212 | \& print STDERR "\en\etThis message should be unadorned.\en"; | |
213 | \& warn "\etThis is a user warning"; | |
214 | \& print "\enDIAGNOSTIC TESTER: Please enter a <CR> here: "; | |
215 | \& my $a, $b = scalar <STDIN>; | |
216 | \& print "\en"; | |
217 | \& print $x/$y; | |
218 | .Ve | |
219 | .PP | |
220 | If you prefer to run your program first and look at its problem | |
221 | afterwards, do this: | |
222 | .PP | |
223 | .Vb 2 | |
224 | \& perl -w test.pl 2>test.out | |
225 | \& ./splain < test.out | |
226 | .Ve | |
227 | .PP | |
228 | Note that this is not in general possible in shells of more dubious heritage, | |
229 | as the theoretical | |
230 | .PP | |
231 | .Vb 2 | |
232 | \& (perl -w test.pl >/dev/tty) >& test.out | |
233 | \& ./splain < test.out | |
234 | .Ve | |
235 | .PP | |
236 | Because you just moved the existing \fBstdout\fR to somewhere else. | |
237 | .PP | |
238 | If you don't want to modify your source code, but still have on-the-fly | |
239 | warnings, do this: | |
240 | .PP | |
241 | .Vb 1 | |
242 | \& exec 3>&1; perl -w test.pl 2>&1 1>&3 3>&- | splain 1>&2 3>&- | |
243 | .Ve | |
244 | .PP | |
245 | Nifty, eh? | |
246 | .PP | |
247 | If you want to control warnings on the fly, do something like this. | |
248 | Make sure you do the \f(CW\*(C`use\*(C'\fR first, or you won't be able to get | |
249 | at the \fIenable()\fR or \fIdisable()\fR methods. | |
250 | .PP | |
251 | .Vb 4 | |
252 | \& use diagnostics; # checks entire compilation phase | |
253 | \& print "\entime for 1st bogus diags: SQUAWKINGS\en"; | |
254 | \& print BOGUS1 'nada'; | |
255 | \& print "done with 1st bogus\en"; | |
256 | .Ve | |
257 | .PP | |
258 | .Vb 4 | |
259 | \& disable diagnostics; # only turns off runtime warnings | |
260 | \& print "\entime for 2nd bogus: (squelched)\en"; | |
261 | \& print BOGUS2 'nada'; | |
262 | \& print "done with 2nd bogus\en"; | |
263 | .Ve | |
264 | .PP | |
265 | .Vb 4 | |
266 | \& enable diagnostics; # turns back on runtime warnings | |
267 | \& print "\entime for 3rd bogus: SQUAWKINGS\en"; | |
268 | \& print BOGUS3 'nada'; | |
269 | \& print "done with 3rd bogus\en"; | |
270 | .Ve | |
271 | .PP | |
272 | .Vb 4 | |
273 | \& disable diagnostics; | |
274 | \& print "\entime for 4th bogus: (squelched)\en"; | |
275 | \& print BOGUS4 'nada'; | |
276 | \& print "done with 4th bogus\en"; | |
277 | .Ve | |
278 | .SH "INTERNALS" | |
279 | .IX Header "INTERNALS" | |
280 | Diagnostic messages derive from the \fIperldiag.pod\fR file when available at | |
281 | runtime. Otherwise, they may be embedded in the file itself when the | |
282 | splain package is built. See the \fIMakefile\fR for details. | |
283 | .PP | |
284 | If an extant \f(CW$SIG\fR{_\|_WARN_\|_} handler is discovered, it will continue | |
285 | to be honored, but only after the \fIdiagnostics::splainthis()\fR function | |
286 | (the module's \f(CW$SIG\fR{_\|_WARN_\|_} interceptor) has had its way with your | |
287 | warnings. | |
288 | .PP | |
289 | There is a \f(CW$diagnostics::DEBUG\fR variable you may set if you're desperately | |
290 | curious what sorts of things are being intercepted. | |
291 | .PP | |
292 | .Vb 1 | |
293 | \& BEGIN { $diagnostics::DEBUG = 1 } | |
294 | .Ve | |
295 | .SH "BUGS" | |
296 | .IX Header "BUGS" | |
297 | Not being able to say \*(L"no diagnostics\*(R" is annoying, but may not be | |
298 | insurmountable. | |
299 | .PP | |
300 | The \f(CW\*(C`\-pretty\*(C'\fR directive is called too late to affect matters. | |
301 | You have to do this instead, and \fIbefore\fR you load the module. | |
302 | .PP | |
303 | .Vb 1 | |
304 | \& BEGIN { $diagnostics::PRETTY = 1 } | |
305 | .Ve | |
306 | .PP | |
307 | I could start up faster by delaying compilation until it should be | |
308 | needed, but this gets a \*(L"panic: top_level\*(R" when using the pragma form | |
309 | in Perl 5.001e. | |
310 | .PP | |
311 | While it's true that this documentation is somewhat subserious, if you use | |
312 | a program named \fIsplain\fR, you should expect a bit of whimsy. | |
313 | .SH "AUTHOR" | |
314 | .IX Header "AUTHOR" | |
315 | Tom Christiansen <\fItchrist@mox.perl.com\fR>, 25 June 1995. |