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1 | =head1 NAME |
2 | |
3 | perldebug - Perl debugging |
4 | |
5 | =head1 DESCRIPTION |
6 | |
7 | First of all, have you tried using the B<-w> switch? |
8 | |
f6b3c421 |
9 | |
10 | If you're new to the Perl debugger, you may prefer to read |
11 | L<perldebtut>, which is a tutorial introduction to the debugger . |
12 | |
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13 | =head1 The Perl Debugger |
14 | |
15 | If you invoke Perl with the B<-d> switch, your script runs under the |
16 | Perl source debugger. This works like an interactive Perl |
17 | environment, prompting for debugger commands that let you examine |
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18 | source code, set breakpoints, get stack backtraces, change the values of |
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19 | variables, etc. This is so convenient that you often fire up |
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20 | the debugger all by itself just to test out Perl constructs |
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21 | interactively to see what they do. For example: |
22 | |
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23 | $ perl -d -e 42 |
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24 | |
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25 | In Perl, the debugger is not a separate program the way it usually is in the |
4e1d3b43 |
26 | typical compiled environment. Instead, the B<-d> flag tells the compiler |
27 | to insert source information into the parse trees it's about to hand off |
28 | to the interpreter. That means your code must first compile correctly |
29 | for the debugger to work on it. Then when the interpreter starts up, it |
055fd3a9 |
30 | preloads a special Perl library file containing the debugger. |
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31 | |
32 | The program will halt I<right before> the first run-time executable |
33 | statement (but see below regarding compile-time statements) and ask you |
34 | to enter a debugger command. Contrary to popular expectations, whenever |
35 | the debugger halts and shows you a line of code, it always displays the |
36 | line it's I<about> to execute, rather than the one it has just executed. |
37 | |
38 | Any command not recognized by the debugger is directly executed |
055fd3a9 |
39 | (C<eval>'d) as Perl code in the current package. (The debugger |
40 | uses the DB package for keeping its own state information.) |
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41 | |
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42 | For any text entered at the debugger prompt, leading and trailing whitespace |
43 | is first stripped before further processing. If a debugger command |
44 | coincides with some function in your own program, merely precede the |
45 | function with something that doesn't look like a debugger command, such |
46 | as a leading C<;> or perhaps a C<+>, or by wrapping it with parentheses |
47 | or braces. |
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48 | |
49 | =head2 Debugger Commands |
50 | |
51 | The debugger understands the following commands: |
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52 | |
53 | =over 12 |
54 | |
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55 | =item h |
56 | |
57 | Prints out a summary help message |
58 | |
4e1d3b43 |
59 | =item h [command] |
60 | |
492652be |
61 | Prints out a help message for the given debugger command. |
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62 | |
492652be |
63 | =item h h |
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64 | |
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65 | The special argument of C<h h> produces the entire help page, which is quite long. |
66 | |
67 | If the output of the C<h h> command (or any command, for that matter) scrolls |
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68 | past your screen, precede the command with a leading pipe symbol so |
69 | that it's run through your pager, as in |
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70 | |
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71 | DB> |h h |
72 | |
73 | You may change the pager which is used via C<o pager=...> command. |
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74 | |
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75 | |
4e1d3b43 |
76 | =item p expr |
77 | |
36477c24 |
78 | Same as C<print {$DB::OUT} expr> in the current package. In particular, |
c997b287 |
79 | because this is just Perl's own C<print> function, this means that nested |
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80 | data structures and objects are not dumped, unlike with the C<x> command. |
81 | |
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82 | The C<DB::OUT> filehandle is opened to F</dev/tty>, regardless of |
83 | where STDOUT may be redirected to. |
84 | |
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85 | =item x [maxdepth] expr |
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86 | |
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87 | Evaluates its expression in list context and dumps out the result in a |
88 | pretty-printed fashion. Nested data structures are printed out |
89 | recursively, unlike the real C<print> function in Perl. When dumping |
90 | hashes, you'll probably prefer 'x \%h' rather than 'x %h'. |
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91 | See L<Dumpvalue> if you'd like to do this yourself. |
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92 | |
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93 | The output format is governed by multiple options described under |
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94 | L<"Configurable Options">. |
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95 | |
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96 | If the C<maxdepth> is included, it must be a numeral I<N>; the value is |
97 | dumped only I<N> levels deep, as if the C<dumpDepth> option had been |
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98 | temporarily set to I<N>. |
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99 | |
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100 | =item V [pkg [vars]] |
101 | |
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102 | Display all (or some) variables in package (defaulting to C<main>) |
103 | using a data pretty-printer (hashes show their keys and values so |
104 | you see what's what, control characters are made printable, etc.). |
105 | Make sure you don't put the type specifier (like C<$>) there, just |
106 | the symbol names, like this: |
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107 | |
108 | V DB filename line |
109 | |
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110 | Use C<~pattern> and C<!pattern> for positive and negative regexes. |
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111 | |
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112 | This is similar to calling the C<x> command on each applicable var. |
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113 | |
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114 | =item X [vars] |
115 | |
116 | Same as C<V currentpackage [vars]>. |
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117 | |
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118 | =item y [level [vars]] |
119 | |
120 | Display all (or some) lexical variables (mnemonic: C<mY> variables) |
121 | in the current scope or I<level> scopes higher. You can limit the |
122 | variables that you see with I<vars> which works exactly as it does |
123 | for the C<V> and C<X> commands. Requires the C<PadWalker> module |
124 | version 0.08 or higher; will warn if this isn't installed. Output |
125 | is pretty-printed in the same style as for C<V> and the format is |
126 | controlled by the same options. |
127 | |
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128 | =item T |
129 | |
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130 | Produce a stack backtrace. See below for details on its output. |
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131 | |
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132 | =item s [expr] |
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133 | |
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134 | Single step. Executes until the beginning of another |
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135 | statement, descending into subroutine calls. If an expression is |
136 | supplied that includes function calls, it too will be single-stepped. |
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137 | |
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138 | =item n [expr] |
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139 | |
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140 | Next. Executes over subroutine calls, until the beginning |
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141 | of the next statement. If an expression is supplied that includes |
142 | function calls, those functions will be executed with stops before |
143 | each statement. |
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144 | |
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145 | =item r |
146 | |
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147 | Continue until the return from the current subroutine. |
148 | Dump the return value if the C<PrintRet> option is set (default). |
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149 | |
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150 | =item <CR> |
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151 | |
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152 | Repeat last C<n> or C<s> command. |
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153 | |
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154 | =item c [line|sub] |
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155 | |
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156 | Continue, optionally inserting a one-time-only breakpoint |
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157 | at the specified line or subroutine. |
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158 | |
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159 | =item l |
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160 | |
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161 | List next window of lines. |
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162 | |
163 | =item l min+incr |
164 | |
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165 | List C<incr+1> lines starting at C<min>. |
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166 | |
167 | =item l min-max |
168 | |
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169 | List lines C<min> through C<max>. C<l -> is synonymous to C<->. |
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170 | |
171 | =item l line |
172 | |
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173 | List a single line. |
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174 | |
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175 | =item l subname |
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176 | |
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177 | List first window of lines from subroutine. I<subname> may |
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178 | be a variable that contains a code reference. |
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179 | |
180 | =item - |
181 | |
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182 | List previous window of lines. |
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183 | |
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184 | =item v [line] |
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185 | |
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186 | View a few lines of code around the current line. |
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187 | |
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188 | =item . |
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189 | |
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190 | Return the internal debugger pointer to the line last |
191 | executed, and print out that line. |
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192 | |
193 | =item f filename |
194 | |
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195 | Switch to viewing a different file or C<eval> statement. If I<filename> |
196 | is not a full pathname found in the values of %INC, it is considered |
197 | a regex. |
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198 | |
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199 | C<eval>ed strings (when accessible) are considered to be filenames: |
200 | C<f (eval 7)> and C<f eval 7\b> access the body of the 7th C<eval>ed string |
055fd3a9 |
201 | (in the order of execution). The bodies of the currently executed C<eval> |
202 | and of C<eval>ed strings that define subroutines are saved and thus |
203 | accessible. |
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204 | |
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205 | =item /pattern/ |
206 | |
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207 | Search forwards for pattern (a Perl regex); final / is optional. |
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208 | The search is case-insensitive by default. |
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209 | |
210 | =item ?pattern? |
211 | |
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212 | Search backwards for pattern; final ? is optional. |
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213 | The search is case-insensitive by default. |
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214 | |
492652be |
215 | =item L [abw] |
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216 | |
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217 | List (default all) actions, breakpoints and watch expressions |
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218 | |
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219 | =item S [[!]regex] |
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220 | |
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221 | List subroutine names [not] matching the regex. |
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222 | |
223 | =item t |
224 | |
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225 | Toggle trace mode (see also the C<AutoTrace> option). |
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226 | |
227 | =item t expr |
228 | |
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229 | Trace through execution of C<expr>. |
230 | See L<perldebguts/"Frame Listing Output Examples"> for examples. |
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231 | |
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232 | =item b |
233 | |
234 | Sets breakpoint on current line |
235 | |
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236 | =item b [line] [condition] |
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237 | |
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238 | Set a breakpoint before the given line. If a condition |
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239 | is specified, it's evaluated each time the statement is reached: a |
240 | breakpoint is taken only if the condition is true. Breakpoints may |
241 | only be set on lines that begin an executable statement. Conditions |
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242 | don't use C<if>: |
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243 | |
244 | b 237 $x > 30 |
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245 | b 237 ++$count237 < 11 |
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246 | b 33 /pattern/i |
247 | |
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248 | =item b subname [condition] |
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249 | |
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250 | Set a breakpoint before the first line of the named subroutine. I<subname> may |
251 | be a variable containing a code reference (in this case I<condition> |
83ee9e09 |
252 | is not supported). |
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253 | |
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254 | =item b postpone subname [condition] |
255 | |
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256 | Set a breakpoint at first line of subroutine after it is compiled. |
36477c24 |
257 | |
258 | =item b load filename |
259 | |
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260 | Set a breakpoint before the first executed line of the I<filename>, |
261 | which should be a full pathname found amongst the %INC values. |
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262 | |
263 | =item b compile subname |
264 | |
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265 | Sets a breakpoint before the first statement executed after the specified |
266 | subroutine is compiled. |
36477c24 |
267 | |
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268 | =item B line |
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269 | |
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270 | Delete a breakpoint from the specified I<line>. |
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271 | |
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272 | =item B * |
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273 | |
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274 | Delete all installed breakpoints. |
275 | |
276 | =item a [line] command |
277 | |
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278 | Set an action to be done before the line is executed. If I<line> is |
279 | omitted, set an action on the line about to be executed. |
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280 | The sequence of steps taken by the debugger is |
281 | |
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282 | 1. check for a breakpoint at this line |
283 | 2. print the line if necessary (tracing) |
284 | 3. do any actions associated with that line |
285 | 4. prompt user if at a breakpoint or in single-step |
286 | 5. evaluate line |
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287 | |
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288 | For example, this will print out $foo every time line |
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289 | 53 is passed: |
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290 | |
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291 | a 53 print "DB FOUND $foo\n" |
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292 | |
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293 | =item A line |
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294 | |
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295 | Delete an action from the specified line. |
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296 | |
492652be |
297 | =item A * |
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298 | |
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299 | Delete all installed actions. |
300 | |
492652be |
301 | =item w expr |
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302 | |
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303 | Add a global watch-expression. We hope you know what one of these |
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304 | is, because they're supposed to be obvious. |
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305 | |
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306 | =item W expr |
307 | |
308 | Delete watch-expression |
309 | |
310 | =item W * |
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311 | |
312 | Delete all watch-expressions. |
313 | |
492652be |
314 | =item o |
315 | |
316 | Display all options |
317 | |
318 | =item o booloption ... |
055fd3a9 |
319 | |
320 | Set each listed Boolean option to the value C<1>. |
321 | |
492652be |
322 | =item o anyoption? ... |
055fd3a9 |
323 | |
324 | Print out the value of one or more options. |
325 | |
492652be |
326 | =item o option=value ... |
055fd3a9 |
327 | |
328 | Set the value of one or more options. If the value has internal |
492652be |
329 | whitespace, it should be quoted. For example, you could set C<o |
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330 | pager="less -MQeicsNfr"> to call B<less> with those specific options. |
331 | You may use either single or double quotes, but if you do, you must |
332 | escape any embedded instances of same sort of quote you began with, |
333 | as well as any escaping any escapes that immediately precede that |
334 | quote but which are not meant to escape the quote itself. In other |
335 | words, you follow single-quoting rules irrespective of the quote; |
492652be |
336 | eg: C<o option='this isn\'t bad'> or C<o option="She said, \"Isn't |
055fd3a9 |
337 | it?\"">. |
338 | |
339 | For historical reasons, the C<=value> is optional, but defaults to |
340 | 1 only where it is safe to do so--that is, mostly for Boolean |
341 | options. It is always better to assign a specific value using C<=>. |
342 | The C<option> can be abbreviated, but for clarity probably should |
13a2d996 |
343 | not be. Several options can be set together. See L<"Configurable Options"> |
344 | for a list of these. |
055fd3a9 |
345 | |
346 | =item < ? |
347 | |
348 | List out all pre-prompt Perl command actions. |
349 | |
350 | =item < [ command ] |
351 | |
352 | Set an action (Perl command) to happen before every debugger prompt. |
353 | A multi-line command may be entered by backslashing the newlines. |
0d6091f7 |
354 | |
355 | =item < * |
356 | |
357 | Delete all pre-prompt Perl command actions. |
055fd3a9 |
358 | |
359 | =item << command |
360 | |
361 | Add an action (Perl command) to happen before every debugger prompt. |
362 | A multi-line command may be entered by backwhacking the newlines. |
363 | |
364 | =item > ? |
365 | |
366 | List out post-prompt Perl command actions. |
367 | |
368 | =item > command |
369 | |
370 | Set an action (Perl command) to happen after the prompt when you've |
371 | just given a command to return to executing the script. A multi-line |
372 | command may be entered by backslashing the newlines (we bet you |
0d6091f7 |
373 | couldn't've guessed this by now). |
374 | |
375 | =item > * |
376 | |
377 | Delete all post-prompt Perl command actions. |
055fd3a9 |
378 | |
379 | =item >> command |
380 | |
381 | Adds an action (Perl command) to happen after the prompt when you've |
382 | just given a command to return to executing the script. A multi-line |
b1866b2d |
383 | command may be entered by backslashing the newlines. |
055fd3a9 |
384 | |
385 | =item { ? |
386 | |
387 | List out pre-prompt debugger commands. |
388 | |
389 | =item { [ command ] |
390 | |
391 | Set an action (debugger command) to happen before every debugger prompt. |
392 | A multi-line command may be entered in the customary fashion. |
055fd3a9 |
393 | |
394 | Because this command is in some senses new, a warning is issued if |
395 | you appear to have accidentally entered a block instead. If that's |
396 | what you mean to do, write it as with C<;{ ... }> or even |
397 | C<do { ... }>. |
398 | |
0d6091f7 |
399 | =item { * |
400 | |
401 | Delete all pre-prompt debugger commands. |
402 | |
055fd3a9 |
403 | =item {{ command |
404 | |
405 | Add an action (debugger command) to happen before every debugger prompt. |
406 | A multi-line command may be entered, if you can guess how: see above. |
407 | |
408 | =item ! number |
409 | |
410 | Redo a previous command (defaults to the previous command). |
411 | |
412 | =item ! -number |
413 | |
414 | Redo number'th previous command. |
415 | |
416 | =item ! pattern |
417 | |
418 | Redo last command that started with pattern. |
492652be |
419 | See C<o recallCommand>, too. |
055fd3a9 |
420 | |
421 | =item !! cmd |
422 | |
423 | Run cmd in a subprocess (reads from DB::IN, writes to DB::OUT) See |
492652be |
424 | C<o shellBang>, also. Note that the user's current shell (well, |
055fd3a9 |
425 | their C<$ENV{SHELL}> variable) will be used, which can interfere |
426 | with proper interpretation of exit status or signal and coredump |
427 | information. |
428 | |
947cb114 |
429 | =item source file |
5bad0d9e |
430 | |
947cb114 |
431 | Read and execute debugger commands from I<file>. |
432 | I<file> may itself contain C<source> commands. |
5bad0d9e |
433 | |
055fd3a9 |
434 | =item H -number |
435 | |
436 | Display last n commands. Only commands longer than one character are |
437 | listed. If I<number> is omitted, list them all. |
438 | |
439 | =item q or ^D |
440 | |
441 | Quit. ("quit" doesn't work for this, unless you've made an alias) |
442 | This is the only supported way to exit the debugger, though typing |
443 | C<exit> twice might work. |
444 | |
445 | Set the C<inhibit_exit> option to 0 if you want to be able to step |
446 | off the end the script. You may also need to set $finished to 0 |
447 | if you want to step through global destruction. |
448 | |
449 | =item R |
450 | |
451 | Restart the debugger by C<exec()>ing a new session. We try to maintain |
452 | your history across this, but internal settings and command-line options |
453 | may be lost. |
454 | |
455 | The following setting are currently preserved: history, breakpoints, |
456 | actions, debugger options, and the Perl command-line |
457 | options B<-w>, B<-I>, and B<-e>. |
458 | |
459 | =item |dbcmd |
460 | |
461 | Run the debugger command, piping DB::OUT into your current pager. |
462 | |
463 | =item ||dbcmd |
464 | |
c997b287 |
465 | Same as C<|dbcmd> but DB::OUT is temporarily C<select>ed as well. |
055fd3a9 |
466 | |
467 | =item = [alias value] |
468 | |
469 | Define a command alias, like |
470 | |
471 | = quit q |
472 | |
473 | or list current aliases. |
474 | |
475 | =item command |
476 | |
477 | Execute command as a Perl statement. A trailing semicolon will be |
478 | supplied. If the Perl statement would otherwise be confused for a |
479 | Perl debugger, use a leading semicolon, too. |
480 | |
481 | =item m expr |
482 | |
483 | List which methods may be called on the result of the evaluated |
484 | expression. The expression may evaluated to a reference to a |
485 | blessed object, or to a package name. |
486 | |
492652be |
487 | =item M |
488 | |
489 | Displays all loaded modules and their versions |
490 | |
491 | |
055fd3a9 |
492 | =item man [manpage] |
493 | |
494 | Despite its name, this calls your system's default documentation |
495 | viewer on the given page, or on the viewer itself if I<manpage> is |
496 | omitted. If that viewer is B<man>, the current C<Config> information |
497 | is used to invoke B<man> using the proper MANPATH or S<B<-M> |
498 | I<manpath>> option. Failed lookups of the form C<XXX> that match |
499 | known manpages of the form I<perlXXX> will be retried. This lets |
500 | you type C<man debug> or C<man op> from the debugger. |
501 | |
502 | On systems traditionally bereft of a usable B<man> command, the |
503 | debugger invokes B<perldoc>. Occasionally this determination is |
504 | incorrect due to recalcitrant vendors or rather more felicitously, |
505 | to enterprising users. If you fall into either category, just |
506 | manually set the $DB::doccmd variable to whatever viewer to view |
507 | the Perl documentation on your system. This may be set in an rc |
508 | file, or through direct assignment. We're still waiting for a |
509 | working example of something along the lines of: |
4e1d3b43 |
510 | |
055fd3a9 |
511 | $DB::doccmd = 'netscape -remote http://something.here/'; |
512 | |
513 | =back |
514 | |
515 | =head2 Configurable Options |
516 | |
492652be |
517 | The debugger has numerous options settable using the C<o> command, |
055fd3a9 |
518 | either interactively or from the environment or an rc file. |
e00d725b |
519 | (./.perldb or ~/.perldb under Unix.) |
520 | |
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521 | |
522 | =over 12 |
523 | |
e7ea3e70 |
524 | =item C<recallCommand>, C<ShellBang> |
4e1d3b43 |
525 | |
526 | The characters used to recall command or spawn shell. By |
055fd3a9 |
527 | default, both are set to C<!>, which is unfortunate. |
4e1d3b43 |
528 | |
e7ea3e70 |
529 | =item C<pager> |
4e1d3b43 |
530 | |
055fd3a9 |
531 | Program to use for output of pager-piped commands (those beginning |
532 | with a C<|> character.) By default, C<$ENV{PAGER}> will be used. |
533 | Because the debugger uses your current terminal characteristics |
534 | for bold and underlining, if the chosen pager does not pass escape |
535 | sequences through unchanged, the output of some debugger commands |
536 | will not be readable when sent through the pager. |
4e1d3b43 |
537 | |
e7ea3e70 |
538 | =item C<tkRunning> |
36477c24 |
539 | |
540 | Run Tk while prompting (with ReadLine). |
541 | |
e7ea3e70 |
542 | =item C<signalLevel>, C<warnLevel>, C<dieLevel> |
543 | |
4c82ae22 |
544 | Level of verbosity. By default, the debugger leaves your exceptions |
545 | and warnings alone, because altering them can break correctly running |
546 | programs. It will attempt to print a message when uncaught INT, BUS, or |
547 | SEGV signals arrive. (But see the mention of signals in L<BUGS> below.) |
548 | |
549 | To disable this default safe mode, set these values to something higher |
550 | than 0. At a level of 1, you get backtraces upon receiving any kind |
551 | of warning (this is often annoying) or exception (this is |
552 | often valuable). Unfortunately, the debugger cannot discern fatal |
553 | exceptions from non-fatal ones. If C<dieLevel> is even 1, then your |
554 | non-fatal exceptions are also traced and unceremoniously altered if they |
555 | came from C<eval'd> strings or from any kind of C<eval> within modules |
556 | you're attempting to load. If C<dieLevel> is 2, the debugger doesn't |
557 | care where they came from: It usurps your exception handler and prints |
558 | out a trace, then modifies all exceptions with its own embellishments. |
559 | This may perhaps be useful for some tracing purposes, but tends to hopelessly |
560 | destroy any program that takes its exception handling seriously. |
36477c24 |
561 | |
e7ea3e70 |
562 | =item C<AutoTrace> |
36477c24 |
563 | |
e7ea3e70 |
564 | Trace mode (similar to C<t> command, but can be put into |
565 | C<PERLDB_OPTS>). |
36477c24 |
566 | |
e7ea3e70 |
567 | =item C<LineInfo> |
36477c24 |
568 | |
e7ea3e70 |
569 | File or pipe to print line number info to. If it is a pipe (say, |
055fd3a9 |
570 | C<|visual_perl_db>), then a short message is used. This is the |
571 | mechanism used to interact with a slave editor or visual debugger, |
572 | such as the special C<vi> or C<emacs> hooks, or the C<ddd> graphical |
573 | debugger. |
36477c24 |
574 | |
575 | =item C<inhibit_exit> |
576 | |
577 | If 0, allows I<stepping off> the end of the script. |
578 | |
54310121 |
579 | =item C<PrintRet> |
36477c24 |
580 | |
04cf9722 |
581 | Print return value after C<r> command if set (default). |
36477c24 |
582 | |
28d1fb14 |
583 | =item C<ornaments> |
584 | |
055fd3a9 |
585 | Affects screen appearance of the command line (see L<Term::ReadLine>). |
586 | There is currently no way to disable these, which can render |
587 | some output illegible on some displays, or with some pagers. |
588 | This is considered a bug. |
28d1fb14 |
589 | |
54310121 |
590 | =item C<frame> |
36477c24 |
591 | |
055fd3a9 |
592 | Affects the printing of messages upon entry and exit from subroutines. If |
36477c24 |
593 | C<frame & 2> is false, messages are printed on entry only. (Printing |
055fd3a9 |
594 | on exit might be useful if interspersed with other messages.) |
36477c24 |
595 | |
055fd3a9 |
596 | If C<frame & 4>, arguments to functions are printed, plus context |
597 | and caller info. If C<frame & 8>, overloaded C<stringify> and |
598 | C<tie>d C<FETCH> is enabled on the printed arguments. If C<frame |
599 | & 16>, the return value from the subroutine is printed. |
28d1fb14 |
600 | |
601 | The length at which the argument list is truncated is governed by the |
602 | next option: |
e7ea3e70 |
603 | |
604 | =item C<maxTraceLen> |
605 | |
055fd3a9 |
606 | Length to truncate the argument list when the C<frame> option's |
e7ea3e70 |
607 | bit 4 is set. |
36477c24 |
608 | |
6f891d7d |
609 | =item C<windowSize> |
610 | |
611 | Change the size of code list window (default is 10 lines). |
612 | |
4e1d3b43 |
613 | =back |
614 | |
615 | The following options affect what happens with C<V>, C<X>, and C<x> |
616 | commands: |
617 | |
618 | =over 12 |
619 | |
e7ea3e70 |
620 | =item C<arrayDepth>, C<hashDepth> |
4e1d3b43 |
621 | |
622 | Print only first N elements ('' for all). |
623 | |
d03c2a1b |
624 | =item C<dumpDepth> |
625 | |
626 | Limit recursion depth to N levels when dumping structures. |
627 | Negative values are interpreted as infinity. Default: infinity. |
628 | |
e7ea3e70 |
629 | =item C<compactDump>, C<veryCompact> |
4e1d3b43 |
630 | |
055fd3a9 |
631 | Change the style of array and hash output. If C<compactDump>, short array |
e7ea3e70 |
632 | may be printed on one line. |
4e1d3b43 |
633 | |
e7ea3e70 |
634 | =item C<globPrint> |
4e1d3b43 |
635 | |
636 | Whether to print contents of globs. |
637 | |
e7ea3e70 |
638 | =item C<DumpDBFiles> |
4e1d3b43 |
639 | |
640 | Dump arrays holding debugged files. |
641 | |
e7ea3e70 |
642 | =item C<DumpPackages> |
4e1d3b43 |
643 | |
644 | Dump symbol tables of packages. |
645 | |
6ee623d5 |
646 | =item C<DumpReused> |
647 | |
648 | Dump contents of "reused" addresses. |
649 | |
e7ea3e70 |
650 | =item C<quote>, C<HighBit>, C<undefPrint> |
651 | |
055fd3a9 |
652 | Change the style of string dump. The default value for C<quote> |
653 | is C<auto>; one can enable double-quotish or single-quotish format |
654 | by setting it to C<"> or C<'>, respectively. By default, characters |
655 | with their high bit set are printed verbatim. |
e7ea3e70 |
656 | |
54310121 |
657 | =item C<UsageOnly> |
4e1d3b43 |
658 | |
055fd3a9 |
659 | Rudimentary per-package memory usage dump. Calculates total |
660 | size of strings found in variables in the package. This does not |
661 | include lexicals in a module's file scope, or lost in closures. |
4e1d3b43 |
662 | |
36477c24 |
663 | =back |
4e1d3b43 |
664 | |
e00d725b |
665 | After the rc file is read, the debugger reads the C<$ENV{PERLDB_OPTS}> |
666 | environment variable and parses this as the remainder of a `O ...' |
667 | line as one might enter at the debugger prompt. You may place the |
668 | initialization options C<TTY>, C<noTTY>, C<ReadLine>, and C<NonStop> |
669 | there. |
36477c24 |
670 | |
055fd3a9 |
671 | If your rc file contains: |
4e1d3b43 |
672 | |
055fd3a9 |
673 | parse_options("NonStop=1 LineInfo=db.out AutoTrace"); |
4e1d3b43 |
674 | |
055fd3a9 |
675 | then your script will run without human intervention, putting trace |
676 | information into the file I<db.out>. (If you interrupt it, you'd |
677 | better reset C<LineInfo> to F</dev/tty> if you expect to see anything.) |
4e1d3b43 |
678 | |
36477c24 |
679 | =over 12 |
4e1d3b43 |
680 | |
36477c24 |
681 | =item C<TTY> |
4e1d3b43 |
682 | |
36477c24 |
683 | The TTY to use for debugging I/O. |
684 | |
36477c24 |
685 | =item C<noTTY> |
686 | |
055fd3a9 |
687 | If set, the debugger goes into C<NonStop> mode and will not connect to a TTY. If |
688 | interrupted (or if control goes to the debugger via explicit setting of |
689 | $DB::signal or $DB::single from the Perl script), it connects to a TTY |
690 | specified in the C<TTY> option at startup, or to a tty found at |
691 | runtime using the C<Term::Rendezvous> module of your choice. |
36477c24 |
692 | |
055fd3a9 |
693 | This module should implement a method named C<new> that returns an object |
200f06d0 |
694 | with two methods: C<IN> and C<OUT>. These should return filehandles to use |
055fd3a9 |
695 | for debugging input and output correspondingly. The C<new> method should |
696 | inspect an argument containing the value of C<$ENV{PERLDB_NOTTY}> at |
697 | startup, or C<"/tmp/perldbtty$$"> otherwise. This file is not |
698 | inspected for proper ownership, so security hazards are theoretically |
699 | possible. |
36477c24 |
700 | |
701 | =item C<ReadLine> |
702 | |
055fd3a9 |
703 | If false, readline support in the debugger is disabled in order |
704 | to debug applications that themselves use ReadLine. |
36477c24 |
705 | |
706 | =item C<NonStop> |
707 | |
055fd3a9 |
708 | If set, the debugger goes into non-interactive mode until interrupted, or |
36477c24 |
709 | programmatically by setting $DB::signal or $DB::single. |
710 | |
711 | =back |
712 | |
713 | Here's an example of using the C<$ENV{PERLDB_OPTS}> variable: |
4e1d3b43 |
714 | |
055fd3a9 |
715 | $ PERLDB_OPTS="NonStop frame=2" perl -d myprogram |
4e1d3b43 |
716 | |
055fd3a9 |
717 | That will run the script B<myprogram> without human intervention, |
718 | printing out the call tree with entry and exit points. Note that |
719 | C<NonStop=1 frame=2> is equivalent to C<N f=2>, and that originally, |
720 | options could be uniquely abbreviated by the first letter (modulo |
721 | the C<Dump*> options). It is nevertheless recommended that you |
722 | always spell them out in full for legibility and future compatibility. |
4e1d3b43 |
723 | |
055fd3a9 |
724 | Other examples include |
a0d0e21e |
725 | |
1472e7de |
726 | $ PERLDB_OPTS="NonStop LineInfo=listing frame=2" perl -d myprogram |
a0d0e21e |
727 | |
055fd3a9 |
728 | which runs script non-interactively, printing info on each entry |
729 | into a subroutine and each executed line into the file named F<listing>. |
730 | (If you interrupt it, you would better reset C<LineInfo> to something |
36477c24 |
731 | "interactive"!) |
732 | |
055fd3a9 |
733 | Other examples include (using standard shell syntax to show environment |
734 | variable settings): |
36477c24 |
735 | |
055fd3a9 |
736 | $ ( PERLDB_OPTS="NonStop frame=1 AutoTrace LineInfo=tperl.out" |
737 | perl -d myprogram ) |
36477c24 |
738 | |
055fd3a9 |
739 | which may be useful for debugging a program that uses C<Term::ReadLine> |
740 | itself. Do not forget to detach your shell from the TTY in the window that |
741 | corresponds to F</dev/ttyXX>, say, by issuing a command like |
36477c24 |
742 | |
e7ea3e70 |
743 | $ sleep 1000000 |
36477c24 |
744 | |
055fd3a9 |
745 | See L<perldebguts/"Debugger Internals"> for details. |
a0d0e21e |
746 | |
e7ea3e70 |
747 | =head2 Debugger input/output |
748 | |
749 | =over 8 |
750 | |
751 | =item Prompt |
752 | |
4e1d3b43 |
753 | The debugger prompt is something like |
754 | |
755 | DB<8> |
756 | |
757 | or even |
758 | |
759 | DB<<17>> |
760 | |
055fd3a9 |
761 | where that number is the command number, and which you'd use to |
762 | access with the built-in B<csh>-like history mechanism. For example, |
763 | C<!17> would repeat command number 17. The depth of the angle |
764 | brackets indicates the nesting depth of the debugger. You could |
765 | get more than one set of brackets, for example, if you'd already |
766 | at a breakpoint and then printed the result of a function call that |
767 | itself has a breakpoint, or you step into an expression via C<s/n/t |
768 | expression> command. |
4e1d3b43 |
769 | |
54310121 |
770 | =item Multiline commands |
e7ea3e70 |
771 | |
4a6725af |
772 | If you want to enter a multi-line command, such as a subroutine |
055fd3a9 |
773 | definition with several statements or a format, escape the newline |
774 | that would normally end the debugger command with a backslash. |
e7ea3e70 |
775 | Here's an example: |
a0d0e21e |
776 | |
4e1d3b43 |
777 | DB<1> for (1..4) { \ |
778 | cont: print "ok\n"; \ |
779 | cont: } |
780 | ok |
781 | ok |
782 | ok |
783 | ok |
784 | |
785 | Note that this business of escaping a newline is specific to interactive |
786 | commands typed into the debugger. |
787 | |
e7ea3e70 |
788 | =item Stack backtrace |
789 | |
68dc0745 |
790 | Here's an example of what a stack backtrace via C<T> command might |
e7ea3e70 |
791 | look like: |
4e1d3b43 |
792 | |
793 | $ = main::infested called from file `Ambulation.pm' line 10 |
794 | @ = Ambulation::legs(1, 2, 3, 4) called from file `camel_flea' line 7 |
795 | $ = main::pests('bactrian', 4) called from file `camel_flea' line 4 |
796 | |
055fd3a9 |
797 | The left-hand character up there indicates the context in which the |
798 | function was called, with C<$> and C<@> meaning scalar or list |
799 | contexts respectively, and C<.> meaning void context (which is |
800 | actually a sort of scalar context). The display above says |
801 | that you were in the function C<main::infested> when you ran the |
802 | stack dump, and that it was called in scalar context from line |
803 | 10 of the file I<Ambulation.pm>, but without any arguments at all, |
804 | meaning it was called as C<&infested>. The next stack frame shows |
805 | that the function C<Ambulation::legs> was called in list context |
806 | from the I<camel_flea> file with four arguments. The last stack |
807 | frame shows that C<main::pests> was called in scalar context, |
808 | also from I<camel_flea>, but from line 4. |
4e1d3b43 |
809 | |
055fd3a9 |
810 | If you execute the C<T> command from inside an active C<use> |
811 | statement, the backtrace will contain both a C<require> frame and |
812 | an C<eval>) frame. |
e7ea3e70 |
813 | |
055fd3a9 |
814 | =item Line Listing Format |
e7ea3e70 |
815 | |
055fd3a9 |
816 | This shows the sorts of output the C<l> command can produce: |
e7ea3e70 |
817 | |
818 | DB<<13>> l |
819 | 101: @i{@i} = (); |
820 | 102:b @isa{@i,$pack} = () |
821 | 103 if(exists $i{$prevpack} || exists $isa{$pack}); |
822 | 104 } |
823 | 105 |
824 | 106 next |
825 | 107==> if(exists $isa{$pack}); |
826 | 108 |
827 | 109:a if ($extra-- > 0) { |
828 | 110: %isa = ($pack,1); |
829 | |
055fd3a9 |
830 | Breakable lines are marked with C<:>. Lines with breakpoints are |
831 | marked by C<b> and those with actions by C<a>. The line that's |
832 | about to be executed is marked by C<< ==> >>. |
e7ea3e70 |
833 | |
003183f2 |
834 | Please be aware that code in debugger listings may not look the same |
835 | as your original source code. Line directives and external source |
836 | filters can alter the code before Perl sees it, causing code to move |
837 | from its original positions or take on entirely different forms. |
838 | |
e7ea3e70 |
839 | =item Frame listing |
840 | |
055fd3a9 |
841 | When the C<frame> option is set, the debugger would print entered (and |
842 | optionally exited) subroutines in different styles. See L<perldebguts> |
843 | for incredibly long examples of these. |
e7ea3e70 |
844 | |
845 | =back |
846 | |
847 | =head2 Debugging compile-time statements |
848 | |
055fd3a9 |
849 | If you have compile-time executable statements (such as code within |
850 | BEGIN and CHECK blocks or C<use> statements), these will I<not> be |
851 | stopped by debugger, although C<require>s and INIT blocks will, and |
852 | compile-time statements can be traced with C<AutoTrace> option set |
853 | in C<PERLDB_OPTS>). From your own Perl code, however, you can |
4e1d3b43 |
854 | transfer control back to the debugger using the following statement, |
855 | which is harmless if the debugger is not running: |
a0d0e21e |
856 | |
857 | $DB::single = 1; |
858 | |
055fd3a9 |
859 | If you set C<$DB::single> to 2, it's equivalent to having |
4e1d3b43 |
860 | just typed the C<n> command, whereas a value of 1 means the C<s> |
861 | command. The C<$DB::trace> variable should be set to 1 to simulate |
862 | having typed the C<t> command. |
863 | |
055fd3a9 |
864 | Another way to debug compile-time code is to start the debugger, set a |
865 | breakpoint on the I<load> of some module: |
e7ea3e70 |
866 | |
867 | DB<7> b load f:/perllib/lib/Carp.pm |
868 | Will stop on load of `f:/perllib/lib/Carp.pm'. |
869 | |
055fd3a9 |
870 | and then restart the debugger using the C<R> command (if possible). One can use C<b |
e7ea3e70 |
871 | compile subname> for the same purpose. |
872 | |
4e1d3b43 |
873 | =head2 Debugger Customization |
a0d0e21e |
874 | |
055fd3a9 |
875 | The debugger probably contains enough configuration hooks that you |
876 | won't ever have to modify it yourself. You may change the behaviour |
492652be |
877 | of debugger from within the debugger using its C<o> command, from |
055fd3a9 |
878 | the command line via the C<PERLDB_OPTS> environment variable, and |
879 | from customization files. |
a0d0e21e |
880 | |
055fd3a9 |
881 | You can do some customization by setting up a F<.perldb> file, which |
a0d0e21e |
882 | contains initialization code. For instance, you could make aliases |
4e1d3b43 |
883 | like these (the last one is one people expect to be there): |
a0d0e21e |
884 | |
4e1d3b43 |
885 | $DB::alias{'len'} = 's/^len(.*)/p length($1)/'; |
a0d0e21e |
886 | $DB::alias{'stop'} = 's/^stop (at|in)/b/'; |
4e1d3b43 |
887 | $DB::alias{'ps'} = 's/^ps\b/p scalar /'; |
055fd3a9 |
888 | $DB::alias{'quit'} = 's/^quit(\s*)/exit/'; |
4e1d3b43 |
889 | |
055fd3a9 |
890 | You can change options from F<.perldb> by using calls like this one; |
36477c24 |
891 | |
892 | parse_options("NonStop=1 LineInfo=db.out AutoTrace=1 frame=2"); |
893 | |
055fd3a9 |
894 | The code is executed in the package C<DB>. Note that F<.perldb> is |
774d564b |
895 | processed before processing C<PERLDB_OPTS>. If F<.perldb> defines the |
055fd3a9 |
896 | subroutine C<afterinit>, that function is called after debugger |
774d564b |
897 | initialization ends. F<.perldb> may be contained in the current |
055fd3a9 |
898 | directory, or in the home directory. Because this file is sourced |
899 | in by Perl and may contain arbitrary commands, for security reasons, |
900 | it must be owned by the superuser or the current user, and writable |
901 | by no one but its owner. |
36477c24 |
902 | |
bea98532 |
903 | You can mock TTY input to debugger by adding arbitrary commands to |
904 | @DB::typeahead. For example, your F<.perldb> file might contain: |
905 | |
906 | sub afterinit { push @DB::typeahead, "b 4", "b 6"; } |
907 | |
908 | Which would attempt to set breakpoints on lines 4 and 6 immediately |
909 | after debugger initilization. Note that @DB::typeahead is not a supported |
910 | interface and is subject to change in future releases. |
911 | |
055fd3a9 |
912 | If you want to modify the debugger, copy F<perl5db.pl> from the |
913 | Perl library to another name and hack it to your heart's content. |
914 | You'll then want to set your C<PERL5DB> environment variable to say |
915 | something like this: |
36477c24 |
916 | |
917 | BEGIN { require "myperl5db.pl" } |
918 | |
055fd3a9 |
919 | As a last resort, you could also use C<PERL5DB> to customize the debugger |
920 | by directly setting internal variables or calling debugger functions. |
921 | |
922 | Note that any variables and functions that are not documented in |
923 | this document (or in L<perldebguts>) are considered for internal |
924 | use only, and as such are subject to change without notice. |
36477c24 |
925 | |
4e1d3b43 |
926 | =head2 Readline Support |
927 | |
055fd3a9 |
928 | As shipped, the only command-line history supplied is a simplistic one |
4e1d3b43 |
929 | that checks for leading exclamation points. However, if you install |
930 | the Term::ReadKey and Term::ReadLine modules from CPAN, you will |
931 | have full editing capabilities much like GNU I<readline>(3) provides. |
932 | Look for these in the F<modules/by-module/Term> directory on CPAN. |
055fd3a9 |
933 | These do not support normal B<vi> command-line editing, however. |
4e1d3b43 |
934 | |
055fd3a9 |
935 | A rudimentary command-line completion is also available. |
e7ea3e70 |
936 | Unfortunately, the names of lexical variables are not available for |
937 | completion. |
938 | |
4e1d3b43 |
939 | =head2 Editor Support for Debugging |
940 | |
055fd3a9 |
941 | If you have the FSF's version of B<emacs> installed on your system, |
942 | it can interact with the Perl debugger to provide an integrated |
943 | software development environment reminiscent of its interactions |
944 | with C debuggers. |
4e1d3b43 |
945 | |
055fd3a9 |
946 | Perl comes with a start file for making B<emacs> act like a |
947 | syntax-directed editor that understands (some of) Perl's syntax. |
948 | Look in the I<emacs> directory of the Perl source distribution. |
4e1d3b43 |
949 | |
055fd3a9 |
950 | A similar setup by Tom Christiansen for interacting with any |
951 | vendor-shipped B<vi> and the X11 window system is also available. |
952 | This works similarly to the integrated multiwindow support that |
953 | B<emacs> provides, where the debugger drives the editor. At the |
954 | time of this writing, however, that tool's eventual location in the |
955 | Perl distribution was uncertain. |
4e1d3b43 |
956 | |
055fd3a9 |
957 | Users of B<vi> should also look into B<vim> and B<gvim>, the mousey |
958 | and windy version, for coloring of Perl keywords. |
a0d0e21e |
959 | |
055fd3a9 |
960 | Note that only perl can truly parse Perl, so all such CASE tools |
961 | fall somewhat short of the mark, especially if you don't program |
962 | your Perl as a C programmer might. |
e7ea3e70 |
963 | |
055fd3a9 |
964 | =head2 The Perl Profiler |
e7ea3e70 |
965 | |
055fd3a9 |
966 | If you wish to supply an alternative debugger for Perl to run, just |
967 | invoke your script with a colon and a package argument given to the |
968 | B<-d> flag. The most popular alternative debuggers for Perl is the |
969 | Perl profiler. Devel::DProf is now included with the standard Perl |
970 | distribution. To profile your Perl program in the file F<mycode.pl>, |
971 | just type: |
36477c24 |
972 | |
055fd3a9 |
973 | $ perl -d:DProf mycode.pl |
36477c24 |
974 | |
055fd3a9 |
975 | When the script terminates the profiler will dump the profile |
976 | information to a file called F<tmon.out>. A tool like B<dprofpp>, |
977 | also supplied with the standard Perl distribution, can be used to |
978 | interpret the information in that profile. |
36477c24 |
979 | |
055fd3a9 |
980 | =head1 Debugging regular expressions |
36477c24 |
981 | |
3d555cb8 |
982 | C<use re 'debug'> enables you to see the gory details of how the Perl |
983 | regular expression engine works. In order to understand this typically |
984 | voluminous output, one must not only have some idea about how regular |
985 | expression matching works in general, but also know how Perl's regular |
986 | expressions are internally compiled into an automaton. These matters |
987 | are explored in some detail in |
055fd3a9 |
988 | L<perldebguts/"Debugging regular expressions">. |
36477c24 |
989 | |
055fd3a9 |
990 | =head1 Debugging memory usage |
36477c24 |
991 | |
055fd3a9 |
992 | Perl contains internal support for reporting its own memory usage, |
993 | but this is a fairly advanced concept that requires some understanding |
994 | of how memory allocation works. |
995 | See L<perldebguts/"Debugging Perl memory usage"> for the details. |
36477c24 |
996 | |
055fd3a9 |
997 | =head1 SEE ALSO |
a0d0e21e |
998 | |
999 | You did try the B<-w> switch, didn't you? |
1000 | |
f6b3c421 |
1001 | L<perldebtut>, |
055fd3a9 |
1002 | L<perldebguts>, |
1003 | L<re>, |
1004 | L<DB>, |
fe854a6f |
1005 | L<Devel::DProf>, |
055fd3a9 |
1006 | L<dprofpp>, |
1007 | L<Dumpvalue>, |
1008 | and |
1009 | L<perlrun>. |
a0d0e21e |
1010 | |
055fd3a9 |
1011 | =head1 BUGS |
1012 | |
1013 | You cannot get stack frame information or in any fashion debug functions |
1014 | that were not compiled by Perl, such as those from C or C++ extensions. |
a0d0e21e |
1015 | |
c997b287 |
1016 | If you alter your @_ arguments in a subroutine (such as with C<shift> |
6edf2346 |
1017 | or C<pop>), the stack backtrace will not show the original values. |
c997b287 |
1018 | |
1019 | The debugger does not currently work in conjunction with the B<-W> |
1020 | command-line switch, because it itself is not free of warnings. |
4c82ae22 |
1021 | |
1022 | If you're in a slow syscall (like C<wait>ing, C<accept>ing, or C<read>ing |
1023 | from your keyboard or a socket) and haven't set up your own C<$SIG{INT}> |
1024 | handler, then you won't be able to CTRL-C your way back to the debugger, |
1025 | because the debugger's own C<$SIG{INT}> handler doesn't understand that |
1026 | it needs to raise an exception to longjmp(3) out of slow syscalls. |