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