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| 129 | .\" ======================================================================== |
| 130 | .\" |
| 131 | .IX Title "diagnostics 3" |
| 132 | .TH diagnostics 3 "2001-09-21" "perl v5.8.8" "Perl Programmers Reference Guide" |
| 133 | .SH "NAME" |
| 134 | diagnostics, splain \- produce verbose warning diagnostics |
| 135 | .SH "SYNOPSIS" |
| 136 | .IX Header "SYNOPSIS" |
| 137 | Using the \f(CW\*(C`diagnostics\*(C'\fR pragma: |
| 138 | .PP |
| 139 | .Vb 2 |
| 140 | \& use diagnostics; |
| 141 | \& use diagnostics -verbose; |
| 142 | .Ve |
| 143 | .PP |
| 144 | .Vb 2 |
| 145 | \& enable diagnostics; |
| 146 | \& disable diagnostics; |
| 147 | .Ve |
| 148 | .PP |
| 149 | Using the \f(CW\*(C`splain\*(C'\fR standalone filter program: |
| 150 | .PP |
| 151 | .Vb 2 |
| 152 | \& perl program 2>diag.out |
| 153 | \& splain [-v] [-p] diag.out |
| 154 | .Ve |
| 155 | .PP |
| 156 | Using diagnostics to get stack traces from a misbehaving script: |
| 157 | .PP |
| 158 | .Vb 1 |
| 159 | \& perl -Mdiagnostics=-traceonly my_script.pl |
| 160 | .Ve |
| 161 | .SH "DESCRIPTION" |
| 162 | .IX Header "DESCRIPTION" |
| 163 | .ie n .Sh "The ""diagnostics"" Pragma" |
| 164 | .el .Sh "The \f(CWdiagnostics\fP Pragma" |
| 165 | .IX Subsection "The diagnostics Pragma" |
| 166 | This module extends the terse diagnostics normally emitted by both the |
| 167 | perl compiler and the perl interpreter (from running perl with a \-w |
| 168 | switch or \f(CW\*(C`use warnings\*(C'\fR), augmenting them with the more |
| 169 | explicative and endearing descriptions found in perldiag. Like the |
| 170 | other pragmata, it affects the compilation phase of your program rather |
| 171 | than merely the execution phase. |
| 172 | .PP |
| 173 | To use in your program as a pragma, merely invoke |
| 174 | .PP |
| 175 | .Vb 1 |
| 176 | \& use diagnostics; |
| 177 | .Ve |
| 178 | .PP |
| 179 | at the start (or near the start) of your program. (Note |
| 180 | that this \fIdoes\fR enable perl's \fB\-w\fR flag.) Your whole |
| 181 | compilation will then be subject(ed :\-) to the enhanced diagnostics. |
| 182 | These still go out \fB\s-1STDERR\s0\fR. |
| 183 | .PP |
| 184 | Due to the interaction between runtime and compiletime issues, |
| 185 | and because it's probably not a very good idea anyway, |
| 186 | you may not use \f(CW\*(C`no diagnostics\*(C'\fR to turn them off at compiletime. |
| 187 | However, you may control their behaviour at runtime using the |
| 188 | \&\fIdisable()\fR and \fIenable()\fR methods to turn them off and on respectively. |
| 189 | .PP |
| 190 | The \fB\-verbose\fR flag first prints out the perldiag introduction before |
| 191 | any other diagnostics. The \f(CW$diagnostics::PRETTY\fR variable can generate nicer |
| 192 | escape sequences for pagers. |
| 193 | .PP |
| 194 | Warnings dispatched from perl itself (or more accurately, those that match |
| 195 | descriptions found in perldiag) are only displayed once (no duplicate |
| 196 | descriptions). User code generated warnings a la \fIwarn()\fR are unaffected, |
| 197 | allowing duplicate user messages to be displayed. |
| 198 | .PP |
| 199 | This module also adds a stack trace to the error message when perl dies. |
| 200 | This is useful for pinpointing what caused the death. The \fB\-traceonly\fR (or |
| 201 | just \fB\-t\fR) flag turns off the explanations of warning messages leaving just |
| 202 | the stack traces. So if your script is dieing, run it again with |
| 203 | .PP |
| 204 | .Vb 1 |
| 205 | \& perl -Mdiagnostics=-traceonly my_bad_script |
| 206 | .Ve |
| 207 | .PP |
| 208 | to see the call stack at the time of death. By supplying the \fB\-warntrace\fR |
| 209 | (or just \fB\-w\fR) flag, any warnings emitted will also come with a stack |
| 210 | trace. |
| 211 | .Sh "The \fIsplain\fP Program" |
| 212 | .IX Subsection "The splain Program" |
| 213 | While apparently a whole nuther program, \fIsplain\fR is actually nothing |
| 214 | more than a link to the (executable) \fIdiagnostics.pm\fR module, as well as |
| 215 | a link to the \fIdiagnostics.pod\fR documentation. The \fB\-v\fR flag is like |
| 216 | the \f(CW\*(C`use diagnostics \-verbose\*(C'\fR directive. |
| 217 | The \fB\-p\fR flag is like the |
| 218 | \&\f(CW$diagnostics::PRETTY\fR variable. Since you're post-processing with |
| 219 | \&\fIsplain\fR, there's no sense in being able to \fIenable()\fR or \fIdisable()\fR processing. |
| 220 | .PP |
| 221 | Output from \fIsplain\fR is directed to \fB\s-1STDOUT\s0\fR, unlike the pragma. |
| 222 | .SH "EXAMPLES" |
| 223 | .IX Header "EXAMPLES" |
| 224 | The following file is certain to trigger a few errors at both |
| 225 | runtime and compiletime: |
| 226 | .PP |
| 227 | .Vb 8 |
| 228 | \& use diagnostics; |
| 229 | \& print NOWHERE "nothing\en"; |
| 230 | \& print STDERR "\en\etThis message should be unadorned.\en"; |
| 231 | \& warn "\etThis is a user warning"; |
| 232 | \& print "\enDIAGNOSTIC TESTER: Please enter a <CR> here: "; |
| 233 | \& my $a, $b = scalar <STDIN>; |
| 234 | \& print "\en"; |
| 235 | \& print $x/$y; |
| 236 | .Ve |
| 237 | .PP |
| 238 | If you prefer to run your program first and look at its problem |
| 239 | afterwards, do this: |
| 240 | .PP |
| 241 | .Vb 2 |
| 242 | \& perl -w test.pl 2>test.out |
| 243 | \& ./splain < test.out |
| 244 | .Ve |
| 245 | .PP |
| 246 | Note that this is not in general possible in shells of more dubious heritage, |
| 247 | as the theoretical |
| 248 | .PP |
| 249 | .Vb 2 |
| 250 | \& (perl -w test.pl >/dev/tty) >& test.out |
| 251 | \& ./splain < test.out |
| 252 | .Ve |
| 253 | .PP |
| 254 | Because you just moved the existing \fBstdout\fR to somewhere else. |
| 255 | .PP |
| 256 | If you don't want to modify your source code, but still have on-the-fly |
| 257 | warnings, do this: |
| 258 | .PP |
| 259 | .Vb 1 |
| 260 | \& exec 3>&1; perl -w test.pl 2>&1 1>&3 3>&- | splain 1>&2 3>&- |
| 261 | .Ve |
| 262 | .PP |
| 263 | Nifty, eh? |
| 264 | .PP |
| 265 | If you want to control warnings on the fly, do something like this. |
| 266 | Make sure you do the \f(CW\*(C`use\*(C'\fR first, or you won't be able to get |
| 267 | at the \fIenable()\fR or \fIdisable()\fR methods. |
| 268 | .PP |
| 269 | .Vb 4 |
| 270 | \& use diagnostics; # checks entire compilation phase |
| 271 | \& print "\entime for 1st bogus diags: SQUAWKINGS\en"; |
| 272 | \& print BOGUS1 'nada'; |
| 273 | \& print "done with 1st bogus\en"; |
| 274 | .Ve |
| 275 | .PP |
| 276 | .Vb 4 |
| 277 | \& disable diagnostics; # only turns off runtime warnings |
| 278 | \& print "\entime for 2nd bogus: (squelched)\en"; |
| 279 | \& print BOGUS2 'nada'; |
| 280 | \& print "done with 2nd bogus\en"; |
| 281 | .Ve |
| 282 | .PP |
| 283 | .Vb 4 |
| 284 | \& enable diagnostics; # turns back on runtime warnings |
| 285 | \& print "\entime for 3rd bogus: SQUAWKINGS\en"; |
| 286 | \& print BOGUS3 'nada'; |
| 287 | \& print "done with 3rd bogus\en"; |
| 288 | .Ve |
| 289 | .PP |
| 290 | .Vb 4 |
| 291 | \& disable diagnostics; |
| 292 | \& print "\entime for 4th bogus: (squelched)\en"; |
| 293 | \& print BOGUS4 'nada'; |
| 294 | \& print "done with 4th bogus\en"; |
| 295 | .Ve |
| 296 | .SH "INTERNALS" |
| 297 | .IX Header "INTERNALS" |
| 298 | Diagnostic messages derive from the \fIperldiag.pod\fR file when available at |
| 299 | runtime. Otherwise, they may be embedded in the file itself when the |
| 300 | splain package is built. See the \fIMakefile\fR for details. |
| 301 | .PP |
| 302 | If an extant \f(CW$SIG\fR{_\|_WARN_\|_} handler is discovered, it will continue |
| 303 | to be honored, but only after the \fIdiagnostics::splainthis()\fR function |
| 304 | (the module's \f(CW$SIG\fR{_\|_WARN_\|_} interceptor) has had its way with your |
| 305 | warnings. |
| 306 | .PP |
| 307 | There is a \f(CW$diagnostics::DEBUG\fR variable you may set if you're desperately |
| 308 | curious what sorts of things are being intercepted. |
| 309 | .PP |
| 310 | .Vb 1 |
| 311 | \& BEGIN { $diagnostics::DEBUG = 1 } |
| 312 | .Ve |
| 313 | .SH "BUGS" |
| 314 | .IX Header "BUGS" |
| 315 | Not being able to say \*(L"no diagnostics\*(R" is annoying, but may not be |
| 316 | insurmountable. |
| 317 | .PP |
| 318 | The \f(CW\*(C`\-pretty\*(C'\fR directive is called too late to affect matters. |
| 319 | You have to do this instead, and \fIbefore\fR you load the module. |
| 320 | .PP |
| 321 | .Vb 1 |
| 322 | \& BEGIN { $diagnostics::PRETTY = 1 } |
| 323 | .Ve |
| 324 | .PP |
| 325 | I could start up faster by delaying compilation until it should be |
| 326 | needed, but this gets a \*(L"panic: top_level\*(R" when using the pragma form |
| 327 | in Perl 5.001e. |
| 328 | .PP |
| 329 | While it's true that this documentation is somewhat subserious, if you use |
| 330 | a program named \fIsplain\fR, you should expect a bit of whimsy. |
| 331 | .SH "AUTHOR" |
| 332 | .IX Header "AUTHOR" |
| 333 | Tom Christiansen <\fItchrist@mox.perl.com\fR>, 25 June 1995. |