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1 | =head1 NAME |
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2 | X<debug> X<debugger> |
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3 | |
4 | perldebug - Perl debugging |
5 | |
6 | =head1 DESCRIPTION |
7 | |
8 | First of all, have you tried using the B<-w> switch? |
9 | |
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10 | |
11 | If you're new to the Perl debugger, you may prefer to read |
12 | L<perldebtut>, which is a tutorial introduction to the debugger . |
13 | |
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14 | =head1 The Perl Debugger |
15 | |
16 | If you invoke Perl with the B<-d> switch, your script runs under the |
17 | Perl source debugger. This works like an interactive Perl |
18 | environment, prompting for debugger commands that let you examine |
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19 | source code, set breakpoints, get stack backtraces, change the values of |
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20 | variables, etc. This is so convenient that you often fire up |
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21 | the debugger all by itself just to test out Perl constructs |
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22 | interactively to see what they do. For example: |
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23 | X<-d> |
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24 | |
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25 | $ perl -d -e 42 |
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26 | |
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27 | In Perl, the debugger is not a separate program the way it usually is in the |
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28 | typical compiled environment. Instead, the B<-d> flag tells the compiler |
29 | to insert source information into the parse trees it's about to hand off |
30 | to the interpreter. That means your code must first compile correctly |
31 | for the debugger to work on it. Then when the interpreter starts up, it |
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32 | preloads a special Perl library file containing the debugger. |
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33 | |
34 | The program will halt I<right before> the first run-time executable |
35 | statement (but see below regarding compile-time statements) and ask you |
36 | to enter a debugger command. Contrary to popular expectations, whenever |
37 | the debugger halts and shows you a line of code, it always displays the |
38 | line it's I<about> to execute, rather than the one it has just executed. |
39 | |
40 | Any command not recognized by the debugger is directly executed |
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41 | (C<eval>'d) as Perl code in the current package. (The debugger |
42 | uses the DB package for keeping its own state information.) |
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43 | |
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44 | Note that the said C<eval> is bound by an implicit scope. As a |
45 | result any newly introduced lexical variable or any modified |
46 | capture buffer content is lost after the eval. The debugger is a |
47 | nice environment to learn Perl, but if you interactively experiment using |
48 | material which should be in the same scope, stuff it in one line. |
49 | |
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50 | For any text entered at the debugger prompt, leading and trailing whitespace |
51 | is first stripped before further processing. If a debugger command |
52 | coincides with some function in your own program, merely precede the |
53 | function with something that doesn't look like a debugger command, such |
54 | as a leading C<;> or perhaps a C<+>, or by wrapping it with parentheses |
55 | or braces. |
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56 | |
57 | =head2 Debugger Commands |
58 | |
59 | The debugger understands the following commands: |
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60 | |
61 | =over 12 |
62 | |
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63 | =item h |
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64 | X<debugger command, h> |
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65 | |
66 | Prints out a summary help message |
67 | |
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68 | =item h [command] |
69 | |
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70 | Prints out a help message for the given debugger command. |
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71 | |
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72 | =item h h |
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73 | |
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74 | The special argument of C<h h> produces the entire help page, which is quite long. |
75 | |
76 | If the output of the C<h h> command (or any command, for that matter) scrolls |
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77 | past your screen, precede the command with a leading pipe symbol so |
78 | that it's run through your pager, as in |
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79 | |
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80 | DB> |h h |
81 | |
82 | You may change the pager which is used via C<o pager=...> command. |
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83 | |
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84 | |
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85 | =item p expr |
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86 | X<debugger command, p> |
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87 | |
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88 | Same as C<print {$DB::OUT} expr> in the current package. In particular, |
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89 | because this is just Perl's own C<print> function, this means that nested |
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90 | data structures and objects are not dumped, unlike with the C<x> command. |
91 | |
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92 | The C<DB::OUT> filehandle is opened to F</dev/tty>, regardless of |
93 | where STDOUT may be redirected to. |
94 | |
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95 | =item x [maxdepth] expr |
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96 | X<debugger command, x> |
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97 | |
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98 | Evaluates its expression in list context and dumps out the result in a |
99 | pretty-printed fashion. Nested data structures are printed out |
100 | recursively, unlike the real C<print> function in Perl. When dumping |
101 | hashes, you'll probably prefer 'x \%h' rather than 'x %h'. |
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102 | See L<Dumpvalue> if you'd like to do this yourself. |
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103 | |
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104 | The output format is governed by multiple options described under |
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105 | L<"Configurable Options">. |
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106 | |
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107 | If the C<maxdepth> is included, it must be a numeral I<N>; the value is |
108 | dumped only I<N> levels deep, as if the C<dumpDepth> option had been |
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109 | temporarily set to I<N>. |
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110 | |
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111 | =item V [pkg [vars]] |
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112 | X<debugger command, V> |
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113 | |
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114 | Display all (or some) variables in package (defaulting to C<main>) |
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115 | using a data pretty-printer (hashes show their keys and values so |
116 | you see what's what, control characters are made printable, etc.). |
117 | Make sure you don't put the type specifier (like C<$>) there, just |
118 | the symbol names, like this: |
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119 | |
120 | V DB filename line |
121 | |
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122 | Use C<~pattern> and C<!pattern> for positive and negative regexes. |
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123 | |
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124 | This is similar to calling the C<x> command on each applicable var. |
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125 | |
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126 | =item X [vars] |
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127 | X<debugger command, X> |
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128 | |
129 | Same as C<V currentpackage [vars]>. |
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130 | |
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131 | =item y [level [vars]] |
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132 | X<debugger command, y> |
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133 | |
134 | Display all (or some) lexical variables (mnemonic: C<mY> variables) |
135 | in the current scope or I<level> scopes higher. You can limit the |
136 | variables that you see with I<vars> which works exactly as it does |
137 | for the C<V> and C<X> commands. Requires the C<PadWalker> module |
138 | version 0.08 or higher; will warn if this isn't installed. Output |
139 | is pretty-printed in the same style as for C<V> and the format is |
140 | controlled by the same options. |
141 | |
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142 | =item T |
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143 | X<debugger command, T> X<backtrace> X<stack, backtrace> |
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144 | |
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145 | Produce a stack backtrace. See below for details on its output. |
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146 | |
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147 | =item s [expr] |
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148 | X<debugger command, s> X<step> |
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149 | |
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150 | Single step. Executes until the beginning of another |
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151 | statement, descending into subroutine calls. If an expression is |
152 | supplied that includes function calls, it too will be single-stepped. |
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153 | |
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154 | =item n [expr] |
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155 | X<debugger command, n> |
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156 | |
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157 | Next. Executes over subroutine calls, until the beginning |
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158 | of the next statement. If an expression is supplied that includes |
159 | function calls, those functions will be executed with stops before |
160 | each statement. |
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161 | |
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162 | =item r |
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163 | X<debugger command, r> |
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164 | |
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165 | Continue until the return from the current subroutine. |
166 | Dump the return value if the C<PrintRet> option is set (default). |
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167 | |
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168 | =item <CR> |
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169 | |
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170 | Repeat last C<n> or C<s> command. |
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171 | |
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172 | =item c [line|sub] |
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173 | X<debugger command, c> |
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174 | |
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175 | Continue, optionally inserting a one-time-only breakpoint |
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176 | at the specified line or subroutine. |
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177 | |
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178 | =item l |
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179 | X<debugger command, l> |
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180 | |
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181 | List next window of lines. |
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182 | |
183 | =item l min+incr |
184 | |
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185 | List C<incr+1> lines starting at C<min>. |
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186 | |
187 | =item l min-max |
188 | |
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189 | List lines C<min> through C<max>. C<l -> is synonymous to C<->. |
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190 | |
191 | =item l line |
192 | |
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193 | List a single line. |
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194 | |
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195 | =item l subname |
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196 | |
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197 | List first window of lines from subroutine. I<subname> may |
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198 | be a variable that contains a code reference. |
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199 | |
200 | =item - |
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201 | X<debugger command, -> |
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202 | |
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203 | List previous window of lines. |
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204 | |
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205 | =item v [line] |
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206 | X<debugger command, v> |
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207 | |
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208 | View a few lines of code around the current line. |
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209 | |
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210 | =item . |
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211 | X<debugger command, .> |
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212 | |
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213 | Return the internal debugger pointer to the line last |
214 | executed, and print out that line. |
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215 | |
216 | =item f filename |
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217 | X<debugger command, f> |
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218 | |
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219 | Switch to viewing a different file or C<eval> statement. If I<filename> |
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220 | is not a full pathname found in the values of %INC, it is considered |
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221 | a regex. |
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222 | |
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223 | C<eval>ed strings (when accessible) are considered to be filenames: |
224 | C<f (eval 7)> and C<f eval 7\b> access the body of the 7th C<eval>ed string |
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225 | (in the order of execution). The bodies of the currently executed C<eval> |
226 | and of C<eval>ed strings that define subroutines are saved and thus |
227 | accessible. |
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228 | |
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229 | =item /pattern/ |
230 | |
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231 | Search forwards for pattern (a Perl regex); final / is optional. |
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232 | The search is case-insensitive by default. |
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233 | |
234 | =item ?pattern? |
235 | |
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236 | Search backwards for pattern; final ? is optional. |
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237 | The search is case-insensitive by default. |
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238 | |
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239 | =item L [abw] |
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240 | X<debugger command, L> |
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241 | |
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242 | List (default all) actions, breakpoints and watch expressions |
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243 | |
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244 | =item S [[!]regex] |
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245 | X<debugger command, S> |
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246 | |
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247 | List subroutine names [not] matching the regex. |
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248 | |
249 | =item t |
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250 | X<debugger command, t> |
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251 | |
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252 | Toggle trace mode (see also the C<AutoTrace> option). |
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253 | |
254 | =item t expr |
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255 | X<debugger command, t> |
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256 | |
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257 | Trace through execution of C<expr>. |
258 | See L<perldebguts/"Frame Listing Output Examples"> for examples. |
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259 | |
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260 | =item b |
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261 | X<breakpoint> |
262 | X<debugger command, b> |
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263 | |
264 | Sets breakpoint on current line |
265 | |
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266 | =item b [line] [condition] |
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267 | X<breakpoint> |
268 | X<debugger command, b> |
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269 | |
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270 | Set a breakpoint before the given line. If a condition |
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271 | is specified, it's evaluated each time the statement is reached: a |
272 | breakpoint is taken only if the condition is true. Breakpoints may |
273 | only be set on lines that begin an executable statement. Conditions |
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274 | don't use C<if>: |
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275 | |
276 | b 237 $x > 30 |
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277 | b 237 ++$count237 < 11 |
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278 | b 33 /pattern/i |
279 | |
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280 | =item b subname [condition] |
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281 | X<breakpoint> |
282 | X<debugger command, b> |
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283 | |
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284 | Set a breakpoint before the first line of the named subroutine. I<subname> may |
285 | be a variable containing a code reference (in this case I<condition> |
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286 | is not supported). |
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287 | |
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288 | =item b postpone subname [condition] |
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289 | X<breakpoint> |
290 | X<debugger command, b> |
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291 | |
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292 | Set a breakpoint at first line of subroutine after it is compiled. |
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293 | |
294 | =item b load filename |
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295 | X<breakpoint> |
296 | X<debugger command, b> |
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297 | |
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298 | Set a breakpoint before the first executed line of the I<filename>, |
299 | which should be a full pathname found amongst the %INC values. |
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300 | |
301 | =item b compile subname |
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302 | X<breakpoint> |
303 | X<debugger command, b> |
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304 | |
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305 | Sets a breakpoint before the first statement executed after the specified |
306 | subroutine is compiled. |
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307 | |
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308 | =item B line |
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309 | X<breakpoint> |
310 | X<debugger command, B> |
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311 | |
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312 | Delete a breakpoint from the specified I<line>. |
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313 | |
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314 | =item B * |
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315 | X<breakpoint> |
316 | X<debugger command, B> |
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317 | |
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318 | Delete all installed breakpoints. |
319 | |
320 | =item a [line] command |
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321 | X<debugger command, a> |
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322 | |
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323 | Set an action to be done before the line is executed. If I<line> is |
324 | omitted, set an action on the line about to be executed. |
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325 | The sequence of steps taken by the debugger is |
326 | |
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327 | 1. check for a breakpoint at this line |
328 | 2. print the line if necessary (tracing) |
329 | 3. do any actions associated with that line |
330 | 4. prompt user if at a breakpoint or in single-step |
331 | 5. evaluate line |
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332 | |
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333 | For example, this will print out $foo every time line |
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334 | 53 is passed: |
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335 | |
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336 | a 53 print "DB FOUND $foo\n" |
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337 | |
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338 | =item A line |
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339 | X<debugger command, A> |
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340 | |
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341 | Delete an action from the specified line. |
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342 | |
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343 | =item A * |
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344 | X<debugger command, A> |
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345 | |
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346 | Delete all installed actions. |
347 | |
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348 | =item w expr |
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349 | X<debugger command, w> |
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350 | |
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351 | Add a global watch-expression. We hope you know what one of these |
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352 | is, because they're supposed to be obvious. |
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353 | |
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354 | =item W expr |
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355 | X<debugger command, W> |
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356 | |
357 | Delete watch-expression |
358 | |
359 | =item W * |
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360 | X<debugger command, W> |
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361 | |
362 | Delete all watch-expressions. |
363 | |
492652be |
364 | =item o |
d74e8afc |
365 | X<debugger command, o> |
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366 | |
367 | Display all options |
368 | |
369 | =item o booloption ... |
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370 | X<debugger command, o> |
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371 | |
372 | Set each listed Boolean option to the value C<1>. |
373 | |
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374 | =item o anyoption? ... |
d74e8afc |
375 | X<debugger command, o> |
055fd3a9 |
376 | |
377 | Print out the value of one or more options. |
378 | |
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379 | =item o option=value ... |
d74e8afc |
380 | X<debugger command, o> |
055fd3a9 |
381 | |
382 | Set the value of one or more options. If the value has internal |
492652be |
383 | whitespace, it should be quoted. For example, you could set C<o |
055fd3a9 |
384 | pager="less -MQeicsNfr"> to call B<less> with those specific options. |
385 | You may use either single or double quotes, but if you do, you must |
386 | escape any embedded instances of same sort of quote you began with, |
387 | as well as any escaping any escapes that immediately precede that |
388 | quote but which are not meant to escape the quote itself. In other |
389 | words, you follow single-quoting rules irrespective of the quote; |
492652be |
390 | eg: C<o option='this isn\'t bad'> or C<o option="She said, \"Isn't |
055fd3a9 |
391 | it?\"">. |
392 | |
393 | For historical reasons, the C<=value> is optional, but defaults to |
394 | 1 only where it is safe to do so--that is, mostly for Boolean |
395 | options. It is always better to assign a specific value using C<=>. |
396 | The C<option> can be abbreviated, but for clarity probably should |
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397 | not be. Several options can be set together. See L<"Configurable Options"> |
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398 | for a list of these. |
055fd3a9 |
399 | |
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400 | =item < ? |
d74e8afc |
401 | X<< debugger command, < >> |
055fd3a9 |
402 | |
403 | List out all pre-prompt Perl command actions. |
404 | |
405 | =item < [ command ] |
d74e8afc |
406 | X<< debugger command, < >> |
055fd3a9 |
407 | |
408 | Set an action (Perl command) to happen before every debugger prompt. |
2e8f3c35 |
409 | A multi-line command may be entered by backslashing the newlines. |
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410 | |
2e8f3c35 |
411 | =item < * |
d74e8afc |
412 | X<< debugger command, < >> |
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413 | |
414 | Delete all pre-prompt Perl command actions. |
055fd3a9 |
415 | |
416 | =item << command |
d74e8afc |
417 | X<< debugger command, << >> |
055fd3a9 |
418 | |
419 | Add an action (Perl command) to happen before every debugger prompt. |
420 | A multi-line command may be entered by backwhacking the newlines. |
421 | |
422 | =item > ? |
d74e8afc |
423 | X<< debugger command, > >> |
055fd3a9 |
424 | |
425 | List out post-prompt Perl command actions. |
426 | |
427 | =item > command |
d74e8afc |
428 | X<< debugger command, > >> |
055fd3a9 |
429 | |
430 | Set an action (Perl command) to happen after the prompt when you've |
431 | just given a command to return to executing the script. A multi-line |
432 | command may be entered by backslashing the newlines (we bet you |
2e8f3c35 |
433 | couldn't've guessed this by now). |
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434 | |
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435 | =item > * |
d74e8afc |
436 | X<< debugger command, > >> |
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437 | |
438 | Delete all post-prompt Perl command actions. |
055fd3a9 |
439 | |
440 | =item >> command |
d74e8afc |
441 | X<<< debugger command, >> >>> |
055fd3a9 |
442 | |
443 | Adds an action (Perl command) to happen after the prompt when you've |
444 | just given a command to return to executing the script. A multi-line |
b1866b2d |
445 | command may be entered by backslashing the newlines. |
055fd3a9 |
446 | |
447 | =item { ? |
d74e8afc |
448 | X<debugger command, {> |
055fd3a9 |
449 | |
450 | List out pre-prompt debugger commands. |
451 | |
452 | =item { [ command ] |
453 | |
454 | Set an action (debugger command) to happen before every debugger prompt. |
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455 | A multi-line command may be entered in the customary fashion. |
055fd3a9 |
456 | |
457 | Because this command is in some senses new, a warning is issued if |
458 | you appear to have accidentally entered a block instead. If that's |
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459 | what you mean to do, write it as with C<;{ ... }> or even |
055fd3a9 |
460 | C<do { ... }>. |
461 | |
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462 | =item { * |
d74e8afc |
463 | X<debugger command, {> |
0d6091f7 |
464 | |
465 | Delete all pre-prompt debugger commands. |
466 | |
055fd3a9 |
467 | =item {{ command |
d74e8afc |
468 | X<debugger command, {{> |
055fd3a9 |
469 | |
470 | Add an action (debugger command) to happen before every debugger prompt. |
471 | A multi-line command may be entered, if you can guess how: see above. |
472 | |
473 | =item ! number |
d74e8afc |
474 | X<debugger command, !> |
055fd3a9 |
475 | |
476 | Redo a previous command (defaults to the previous command). |
477 | |
478 | =item ! -number |
d74e8afc |
479 | X<debugger command, !> |
055fd3a9 |
480 | |
481 | Redo number'th previous command. |
482 | |
483 | =item ! pattern |
d74e8afc |
484 | X<debugger command, !> |
055fd3a9 |
485 | |
486 | Redo last command that started with pattern. |
492652be |
487 | See C<o recallCommand>, too. |
055fd3a9 |
488 | |
489 | =item !! cmd |
d74e8afc |
490 | X<debugger command, !!> |
055fd3a9 |
491 | |
492 | Run cmd in a subprocess (reads from DB::IN, writes to DB::OUT) See |
492652be |
493 | C<o shellBang>, also. Note that the user's current shell (well, |
055fd3a9 |
494 | their C<$ENV{SHELL}> variable) will be used, which can interfere |
495 | with proper interpretation of exit status or signal and coredump |
496 | information. |
497 | |
947cb114 |
498 | =item source file |
d74e8afc |
499 | X<debugger command, source> |
5bad0d9e |
500 | |
947cb114 |
501 | Read and execute debugger commands from I<file>. |
502 | I<file> may itself contain C<source> commands. |
5bad0d9e |
503 | |
055fd3a9 |
504 | =item H -number |
d74e8afc |
505 | X<debugger command, H> |
055fd3a9 |
506 | |
507 | Display last n commands. Only commands longer than one character are |
508 | listed. If I<number> is omitted, list them all. |
509 | |
510 | =item q or ^D |
d74e8afc |
511 | X<debugger command, q> |
512 | X<debugger command, ^D> |
055fd3a9 |
513 | |
514 | Quit. ("quit" doesn't work for this, unless you've made an alias) |
515 | This is the only supported way to exit the debugger, though typing |
516 | C<exit> twice might work. |
517 | |
518 | Set the C<inhibit_exit> option to 0 if you want to be able to step |
2e8f3c35 |
519 | off the end the script. You may also need to set $finished to 0 |
055fd3a9 |
520 | if you want to step through global destruction. |
521 | |
522 | =item R |
d74e8afc |
523 | X<debugger command, R> |
055fd3a9 |
524 | |
525 | Restart the debugger by C<exec()>ing a new session. We try to maintain |
526 | your history across this, but internal settings and command-line options |
527 | may be lost. |
528 | |
529 | The following setting are currently preserved: history, breakpoints, |
530 | actions, debugger options, and the Perl command-line |
531 | options B<-w>, B<-I>, and B<-e>. |
532 | |
533 | =item |dbcmd |
d74e8afc |
534 | X<debugger command, |> |
055fd3a9 |
535 | |
536 | Run the debugger command, piping DB::OUT into your current pager. |
537 | |
538 | =item ||dbcmd |
d74e8afc |
539 | X<debugger command, ||> |
055fd3a9 |
540 | |
c997b287 |
541 | Same as C<|dbcmd> but DB::OUT is temporarily C<select>ed as well. |
055fd3a9 |
542 | |
543 | =item = [alias value] |
d74e8afc |
544 | X<debugger command, => |
055fd3a9 |
545 | |
546 | Define a command alias, like |
547 | |
548 | = quit q |
549 | |
550 | or list current aliases. |
551 | |
552 | =item command |
553 | |
554 | Execute command as a Perl statement. A trailing semicolon will be |
555 | supplied. If the Perl statement would otherwise be confused for a |
556 | Perl debugger, use a leading semicolon, too. |
557 | |
558 | =item m expr |
d74e8afc |
559 | X<debugger command, m> |
055fd3a9 |
560 | |
561 | List which methods may be called on the result of the evaluated |
2e8f3c35 |
562 | expression. The expression may evaluated to a reference to a |
055fd3a9 |
563 | blessed object, or to a package name. |
564 | |
492652be |
565 | =item M |
d74e8afc |
566 | X<debugger command, M> |
492652be |
567 | |
568 | Displays all loaded modules and their versions |
569 | |
570 | |
055fd3a9 |
571 | =item man [manpage] |
d74e8afc |
572 | X<debugger command, man> |
055fd3a9 |
573 | |
574 | Despite its name, this calls your system's default documentation |
575 | viewer on the given page, or on the viewer itself if I<manpage> is |
576 | omitted. If that viewer is B<man>, the current C<Config> information |
577 | is used to invoke B<man> using the proper MANPATH or S<B<-M> |
578 | I<manpath>> option. Failed lookups of the form C<XXX> that match |
579 | known manpages of the form I<perlXXX> will be retried. This lets |
580 | you type C<man debug> or C<man op> from the debugger. |
581 | |
582 | On systems traditionally bereft of a usable B<man> command, the |
583 | debugger invokes B<perldoc>. Occasionally this determination is |
584 | incorrect due to recalcitrant vendors or rather more felicitously, |
585 | to enterprising users. If you fall into either category, just |
586 | manually set the $DB::doccmd variable to whatever viewer to view |
587 | the Perl documentation on your system. This may be set in an rc |
588 | file, or through direct assignment. We're still waiting for a |
589 | working example of something along the lines of: |
4e1d3b43 |
590 | |
055fd3a9 |
591 | $DB::doccmd = 'netscape -remote http://something.here/'; |
592 | |
593 | =back |
594 | |
595 | =head2 Configurable Options |
596 | |
492652be |
597 | The debugger has numerous options settable using the C<o> command, |
055fd3a9 |
598 | either interactively or from the environment or an rc file. |
e00d725b |
599 | (./.perldb or ~/.perldb under Unix.) |
600 | |
4e1d3b43 |
601 | |
602 | =over 12 |
603 | |
e7ea3e70 |
604 | =item C<recallCommand>, C<ShellBang> |
d74e8afc |
605 | X<debugger option, recallCommand> |
606 | X<debugger option, ShellBang> |
4e1d3b43 |
607 | |
608 | The characters used to recall command or spawn shell. By |
055fd3a9 |
609 | default, both are set to C<!>, which is unfortunate. |
4e1d3b43 |
610 | |
e7ea3e70 |
611 | =item C<pager> |
d74e8afc |
612 | X<debugger option, pager> |
4e1d3b43 |
613 | |
055fd3a9 |
614 | Program to use for output of pager-piped commands (those beginning |
615 | with a C<|> character.) By default, C<$ENV{PAGER}> will be used. |
616 | Because the debugger uses your current terminal characteristics |
617 | for bold and underlining, if the chosen pager does not pass escape |
618 | sequences through unchanged, the output of some debugger commands |
619 | will not be readable when sent through the pager. |
4e1d3b43 |
620 | |
e7ea3e70 |
621 | =item C<tkRunning> |
d74e8afc |
622 | X<debugger option, tkRunning> |
36477c24 |
623 | |
624 | Run Tk while prompting (with ReadLine). |
625 | |
e7ea3e70 |
626 | =item C<signalLevel>, C<warnLevel>, C<dieLevel> |
d74e8afc |
627 | X<debugger option, signalLevel> X<debugger option, warnLevel> |
628 | X<debugger option, dieLevel> |
e7ea3e70 |
629 | |
4c82ae22 |
630 | Level of verbosity. By default, the debugger leaves your exceptions |
631 | and warnings alone, because altering them can break correctly running |
632 | programs. It will attempt to print a message when uncaught INT, BUS, or |
633 | SEGV signals arrive. (But see the mention of signals in L<BUGS> below.) |
634 | |
635 | To disable this default safe mode, set these values to something higher |
636 | than 0. At a level of 1, you get backtraces upon receiving any kind |
637 | of warning (this is often annoying) or exception (this is |
638 | often valuable). Unfortunately, the debugger cannot discern fatal |
639 | exceptions from non-fatal ones. If C<dieLevel> is even 1, then your |
640 | non-fatal exceptions are also traced and unceremoniously altered if they |
641 | came from C<eval'd> strings or from any kind of C<eval> within modules |
642 | you're attempting to load. If C<dieLevel> is 2, the debugger doesn't |
643 | care where they came from: It usurps your exception handler and prints |
644 | out a trace, then modifies all exceptions with its own embellishments. |
645 | This may perhaps be useful for some tracing purposes, but tends to hopelessly |
646 | destroy any program that takes its exception handling seriously. |
36477c24 |
647 | |
e7ea3e70 |
648 | =item C<AutoTrace> |
d74e8afc |
649 | X<debugger option, AutoTrace> |
36477c24 |
650 | |
e7ea3e70 |
651 | Trace mode (similar to C<t> command, but can be put into |
652 | C<PERLDB_OPTS>). |
36477c24 |
653 | |
e7ea3e70 |
654 | =item C<LineInfo> |
d74e8afc |
655 | X<debugger option, LineInfo> |
36477c24 |
656 | |
e7ea3e70 |
657 | File or pipe to print line number info to. If it is a pipe (say, |
055fd3a9 |
658 | C<|visual_perl_db>), then a short message is used. This is the |
659 | mechanism used to interact with a slave editor or visual debugger, |
660 | such as the special C<vi> or C<emacs> hooks, or the C<ddd> graphical |
661 | debugger. |
36477c24 |
662 | |
663 | =item C<inhibit_exit> |
d74e8afc |
664 | X<debugger option, inhibit_exit> |
36477c24 |
665 | |
666 | If 0, allows I<stepping off> the end of the script. |
667 | |
54310121 |
668 | =item C<PrintRet> |
d74e8afc |
669 | X<debugger option, PrintRet> |
36477c24 |
670 | |
04cf9722 |
671 | Print return value after C<r> command if set (default). |
36477c24 |
672 | |
28d1fb14 |
673 | =item C<ornaments> |
d74e8afc |
674 | X<debugger option, ornaments> |
28d1fb14 |
675 | |
055fd3a9 |
676 | Affects screen appearance of the command line (see L<Term::ReadLine>). |
677 | There is currently no way to disable these, which can render |
678 | some output illegible on some displays, or with some pagers. |
679 | This is considered a bug. |
28d1fb14 |
680 | |
54310121 |
681 | =item C<frame> |
d74e8afc |
682 | X<debugger option, frame> |
36477c24 |
683 | |
055fd3a9 |
684 | Affects the printing of messages upon entry and exit from subroutines. If |
36477c24 |
685 | C<frame & 2> is false, messages are printed on entry only. (Printing |
055fd3a9 |
686 | on exit might be useful if interspersed with other messages.) |
36477c24 |
687 | |
055fd3a9 |
688 | If C<frame & 4>, arguments to functions are printed, plus context |
689 | and caller info. If C<frame & 8>, overloaded C<stringify> and |
690 | C<tie>d C<FETCH> is enabled on the printed arguments. If C<frame |
691 | & 16>, the return value from the subroutine is printed. |
28d1fb14 |
692 | |
693 | The length at which the argument list is truncated is governed by the |
694 | next option: |
e7ea3e70 |
695 | |
696 | =item C<maxTraceLen> |
d74e8afc |
697 | X<debugger option, maxTraceLen> |
e7ea3e70 |
698 | |
055fd3a9 |
699 | Length to truncate the argument list when the C<frame> option's |
e7ea3e70 |
700 | bit 4 is set. |
36477c24 |
701 | |
6f891d7d |
702 | =item C<windowSize> |
d74e8afc |
703 | X<debugger option, windowSize> |
6f891d7d |
704 | |
705 | Change the size of code list window (default is 10 lines). |
706 | |
4e1d3b43 |
707 | =back |
708 | |
709 | The following options affect what happens with C<V>, C<X>, and C<x> |
710 | commands: |
711 | |
712 | =over 12 |
713 | |
e7ea3e70 |
714 | =item C<arrayDepth>, C<hashDepth> |
d74e8afc |
715 | X<debugger option, arrayDepth> X<debugger option, hashDepth> |
4e1d3b43 |
716 | |
717 | Print only first N elements ('' for all). |
718 | |
d03c2a1b |
719 | =item C<dumpDepth> |
d74e8afc |
720 | X<debugger option, dumpDepth> |
d03c2a1b |
721 | |
722 | Limit recursion depth to N levels when dumping structures. |
723 | Negative values are interpreted as infinity. Default: infinity. |
724 | |
e7ea3e70 |
725 | =item C<compactDump>, C<veryCompact> |
d74e8afc |
726 | X<debugger option, compactDump> X<debugger option, veryCompact> |
4e1d3b43 |
727 | |
055fd3a9 |
728 | Change the style of array and hash output. If C<compactDump>, short array |
e7ea3e70 |
729 | may be printed on one line. |
4e1d3b43 |
730 | |
e7ea3e70 |
731 | =item C<globPrint> |
d74e8afc |
732 | X<debugger option, globPrint> |
4e1d3b43 |
733 | |
734 | Whether to print contents of globs. |
735 | |
e7ea3e70 |
736 | =item C<DumpDBFiles> |
d74e8afc |
737 | X<debugger option, DumpDBFiles> |
4e1d3b43 |
738 | |
739 | Dump arrays holding debugged files. |
740 | |
e7ea3e70 |
741 | =item C<DumpPackages> |
d74e8afc |
742 | X<debugger option, DumpPackages> |
4e1d3b43 |
743 | |
744 | Dump symbol tables of packages. |
745 | |
6ee623d5 |
746 | =item C<DumpReused> |
d74e8afc |
747 | X<debugger option, DumpReused> |
6ee623d5 |
748 | |
749 | Dump contents of "reused" addresses. |
750 | |
e7ea3e70 |
751 | =item C<quote>, C<HighBit>, C<undefPrint> |
d74e8afc |
752 | X<debugger option, quote> X<debugger option, HighBit> |
753 | X<debugger option, undefPrint> |
e7ea3e70 |
754 | |
055fd3a9 |
755 | Change the style of string dump. The default value for C<quote> |
756 | is C<auto>; one can enable double-quotish or single-quotish format |
757 | by setting it to C<"> or C<'>, respectively. By default, characters |
758 | with their high bit set are printed verbatim. |
e7ea3e70 |
759 | |
54310121 |
760 | =item C<UsageOnly> |
d74e8afc |
761 | X<debugger option, UsageOnly> |
4e1d3b43 |
762 | |
055fd3a9 |
763 | Rudimentary per-package memory usage dump. Calculates total |
764 | size of strings found in variables in the package. This does not |
765 | include lexicals in a module's file scope, or lost in closures. |
4e1d3b43 |
766 | |
36477c24 |
767 | =back |
4e1d3b43 |
768 | |
e00d725b |
769 | After the rc file is read, the debugger reads the C<$ENV{PERLDB_OPTS}> |
66a1b24b |
770 | environment variable and parses this as the remainder of a "O ..." |
e00d725b |
771 | line as one might enter at the debugger prompt. You may place the |
772 | initialization options C<TTY>, C<noTTY>, C<ReadLine>, and C<NonStop> |
773 | there. |
36477c24 |
774 | |
055fd3a9 |
775 | If your rc file contains: |
4e1d3b43 |
776 | |
055fd3a9 |
777 | parse_options("NonStop=1 LineInfo=db.out AutoTrace"); |
4e1d3b43 |
778 | |
055fd3a9 |
779 | then your script will run without human intervention, putting trace |
780 | information into the file I<db.out>. (If you interrupt it, you'd |
781 | better reset C<LineInfo> to F</dev/tty> if you expect to see anything.) |
4e1d3b43 |
782 | |
36477c24 |
783 | =over 12 |
4e1d3b43 |
784 | |
36477c24 |
785 | =item C<TTY> |
d74e8afc |
786 | X<debugger option, TTY> |
4e1d3b43 |
787 | |
36477c24 |
788 | The TTY to use for debugging I/O. |
789 | |
36477c24 |
790 | =item C<noTTY> |
d74e8afc |
791 | X<debugger option, noTTY> |
36477c24 |
792 | |
055fd3a9 |
793 | If set, the debugger goes into C<NonStop> mode and will not connect to a TTY. If |
794 | interrupted (or if control goes to the debugger via explicit setting of |
795 | $DB::signal or $DB::single from the Perl script), it connects to a TTY |
796 | specified in the C<TTY> option at startup, or to a tty found at |
797 | runtime using the C<Term::Rendezvous> module of your choice. |
36477c24 |
798 | |
055fd3a9 |
799 | This module should implement a method named C<new> that returns an object |
200f06d0 |
800 | with two methods: C<IN> and C<OUT>. These should return filehandles to use |
055fd3a9 |
801 | for debugging input and output correspondingly. The C<new> method should |
802 | inspect an argument containing the value of C<$ENV{PERLDB_NOTTY}> at |
2e8f3c35 |
803 | startup, or C<"$ENV{HOME}/.perldbtty$$"> otherwise. This file is not |
055fd3a9 |
804 | inspected for proper ownership, so security hazards are theoretically |
805 | possible. |
36477c24 |
806 | |
807 | =item C<ReadLine> |
d74e8afc |
808 | X<debugger option, ReadLine> |
36477c24 |
809 | |
055fd3a9 |
810 | If false, readline support in the debugger is disabled in order |
811 | to debug applications that themselves use ReadLine. |
36477c24 |
812 | |
813 | =item C<NonStop> |
d74e8afc |
814 | X<debugger option, NonStop> |
36477c24 |
815 | |
055fd3a9 |
816 | If set, the debugger goes into non-interactive mode until interrupted, or |
36477c24 |
817 | programmatically by setting $DB::signal or $DB::single. |
818 | |
819 | =back |
820 | |
821 | Here's an example of using the C<$ENV{PERLDB_OPTS}> variable: |
4e1d3b43 |
822 | |
055fd3a9 |
823 | $ PERLDB_OPTS="NonStop frame=2" perl -d myprogram |
4e1d3b43 |
824 | |
055fd3a9 |
825 | That will run the script B<myprogram> without human intervention, |
826 | printing out the call tree with entry and exit points. Note that |
827 | C<NonStop=1 frame=2> is equivalent to C<N f=2>, and that originally, |
828 | options could be uniquely abbreviated by the first letter (modulo |
829 | the C<Dump*> options). It is nevertheless recommended that you |
830 | always spell them out in full for legibility and future compatibility. |
4e1d3b43 |
831 | |
055fd3a9 |
832 | Other examples include |
a0d0e21e |
833 | |
1472e7de |
834 | $ PERLDB_OPTS="NonStop LineInfo=listing frame=2" perl -d myprogram |
a0d0e21e |
835 | |
055fd3a9 |
836 | which runs script non-interactively, printing info on each entry |
837 | into a subroutine and each executed line into the file named F<listing>. |
838 | (If you interrupt it, you would better reset C<LineInfo> to something |
36477c24 |
839 | "interactive"!) |
840 | |
055fd3a9 |
841 | Other examples include (using standard shell syntax to show environment |
842 | variable settings): |
36477c24 |
843 | |
055fd3a9 |
844 | $ ( PERLDB_OPTS="NonStop frame=1 AutoTrace LineInfo=tperl.out" |
845 | perl -d myprogram ) |
36477c24 |
846 | |
055fd3a9 |
847 | which may be useful for debugging a program that uses C<Term::ReadLine> |
848 | itself. Do not forget to detach your shell from the TTY in the window that |
849 | corresponds to F</dev/ttyXX>, say, by issuing a command like |
36477c24 |
850 | |
e7ea3e70 |
851 | $ sleep 1000000 |
36477c24 |
852 | |
055fd3a9 |
853 | See L<perldebguts/"Debugger Internals"> for details. |
a0d0e21e |
854 | |
e7ea3e70 |
855 | =head2 Debugger input/output |
856 | |
857 | =over 8 |
858 | |
859 | =item Prompt |
860 | |
4e1d3b43 |
861 | The debugger prompt is something like |
862 | |
863 | DB<8> |
864 | |
865 | or even |
866 | |
867 | DB<<17>> |
868 | |
055fd3a9 |
869 | where that number is the command number, and which you'd use to |
870 | access with the built-in B<csh>-like history mechanism. For example, |
871 | C<!17> would repeat command number 17. The depth of the angle |
872 | brackets indicates the nesting depth of the debugger. You could |
873 | get more than one set of brackets, for example, if you'd already |
874 | at a breakpoint and then printed the result of a function call that |
875 | itself has a breakpoint, or you step into an expression via C<s/n/t |
876 | expression> command. |
4e1d3b43 |
877 | |
54310121 |
878 | =item Multiline commands |
e7ea3e70 |
879 | |
4a6725af |
880 | If you want to enter a multi-line command, such as a subroutine |
055fd3a9 |
881 | definition with several statements or a format, escape the newline |
882 | that would normally end the debugger command with a backslash. |
e7ea3e70 |
883 | Here's an example: |
a0d0e21e |
884 | |
4e1d3b43 |
885 | DB<1> for (1..4) { \ |
886 | cont: print "ok\n"; \ |
887 | cont: } |
888 | ok |
889 | ok |
890 | ok |
891 | ok |
892 | |
893 | Note that this business of escaping a newline is specific to interactive |
894 | commands typed into the debugger. |
895 | |
e7ea3e70 |
896 | =item Stack backtrace |
d74e8afc |
897 | X<backtrace> X<stack, backtrace> |
e7ea3e70 |
898 | |
68dc0745 |
899 | Here's an example of what a stack backtrace via C<T> command might |
e7ea3e70 |
900 | look like: |
4e1d3b43 |
901 | |
902 | $ = main::infested called from file `Ambulation.pm' line 10 |
903 | @ = Ambulation::legs(1, 2, 3, 4) called from file `camel_flea' line 7 |
904 | $ = main::pests('bactrian', 4) called from file `camel_flea' line 4 |
905 | |
055fd3a9 |
906 | The left-hand character up there indicates the context in which the |
907 | function was called, with C<$> and C<@> meaning scalar or list |
908 | contexts respectively, and C<.> meaning void context (which is |
909 | actually a sort of scalar context). The display above says |
910 | that you were in the function C<main::infested> when you ran the |
911 | stack dump, and that it was called in scalar context from line |
912 | 10 of the file I<Ambulation.pm>, but without any arguments at all, |
913 | meaning it was called as C<&infested>. The next stack frame shows |
914 | that the function C<Ambulation::legs> was called in list context |
915 | from the I<camel_flea> file with four arguments. The last stack |
916 | frame shows that C<main::pests> was called in scalar context, |
917 | also from I<camel_flea>, but from line 4. |
4e1d3b43 |
918 | |
055fd3a9 |
919 | If you execute the C<T> command from inside an active C<use> |
920 | statement, the backtrace will contain both a C<require> frame and |
921 | an C<eval>) frame. |
e7ea3e70 |
922 | |
055fd3a9 |
923 | =item Line Listing Format |
e7ea3e70 |
924 | |
055fd3a9 |
925 | This shows the sorts of output the C<l> command can produce: |
e7ea3e70 |
926 | |
927 | DB<<13>> l |
928 | 101: @i{@i} = (); |
929 | 102:b @isa{@i,$pack} = () |
930 | 103 if(exists $i{$prevpack} || exists $isa{$pack}); |
931 | 104 } |
932 | 105 |
933 | 106 next |
934 | 107==> if(exists $isa{$pack}); |
935 | 108 |
936 | 109:a if ($extra-- > 0) { |
937 | 110: %isa = ($pack,1); |
938 | |
055fd3a9 |
939 | Breakable lines are marked with C<:>. Lines with breakpoints are |
940 | marked by C<b> and those with actions by C<a>. The line that's |
941 | about to be executed is marked by C<< ==> >>. |
e7ea3e70 |
942 | |
003183f2 |
943 | Please be aware that code in debugger listings may not look the same |
944 | as your original source code. Line directives and external source |
945 | filters can alter the code before Perl sees it, causing code to move |
946 | from its original positions or take on entirely different forms. |
947 | |
e7ea3e70 |
948 | =item Frame listing |
949 | |
055fd3a9 |
950 | When the C<frame> option is set, the debugger would print entered (and |
951 | optionally exited) subroutines in different styles. See L<perldebguts> |
952 | for incredibly long examples of these. |
e7ea3e70 |
953 | |
954 | =back |
955 | |
956 | =head2 Debugging compile-time statements |
957 | |
055fd3a9 |
958 | If you have compile-time executable statements (such as code within |
3c10abe3 |
959 | BEGIN, UNITCHECK and CHECK blocks or C<use> statements), these will |
960 | I<not> be stopped by debugger, although C<require>s and INIT blocks |
961 | will, and compile-time statements can be traced with C<AutoTrace> |
962 | option set in C<PERLDB_OPTS>). From your own Perl code, however, you |
963 | can transfer control back to the debugger using the following |
964 | statement, which is harmless if the debugger is not running: |
a0d0e21e |
965 | |
966 | $DB::single = 1; |
967 | |
055fd3a9 |
968 | If you set C<$DB::single> to 2, it's equivalent to having |
4e1d3b43 |
969 | just typed the C<n> command, whereas a value of 1 means the C<s> |
970 | command. The C<$DB::trace> variable should be set to 1 to simulate |
971 | having typed the C<t> command. |
972 | |
055fd3a9 |
973 | Another way to debug compile-time code is to start the debugger, set a |
974 | breakpoint on the I<load> of some module: |
e7ea3e70 |
975 | |
976 | DB<7> b load f:/perllib/lib/Carp.pm |
977 | Will stop on load of `f:/perllib/lib/Carp.pm'. |
978 | |
055fd3a9 |
979 | and then restart the debugger using the C<R> command (if possible). One can use C<b |
e7ea3e70 |
980 | compile subname> for the same purpose. |
981 | |
4e1d3b43 |
982 | =head2 Debugger Customization |
a0d0e21e |
983 | |
055fd3a9 |
984 | The debugger probably contains enough configuration hooks that you |
985 | won't ever have to modify it yourself. You may change the behaviour |
492652be |
986 | of debugger from within the debugger using its C<o> command, from |
055fd3a9 |
987 | the command line via the C<PERLDB_OPTS> environment variable, and |
988 | from customization files. |
a0d0e21e |
989 | |
055fd3a9 |
990 | You can do some customization by setting up a F<.perldb> file, which |
a0d0e21e |
991 | contains initialization code. For instance, you could make aliases |
4e1d3b43 |
992 | like these (the last one is one people expect to be there): |
a0d0e21e |
993 | |
4e1d3b43 |
994 | $DB::alias{'len'} = 's/^len(.*)/p length($1)/'; |
a0d0e21e |
995 | $DB::alias{'stop'} = 's/^stop (at|in)/b/'; |
4e1d3b43 |
996 | $DB::alias{'ps'} = 's/^ps\b/p scalar /'; |
055fd3a9 |
997 | $DB::alias{'quit'} = 's/^quit(\s*)/exit/'; |
4e1d3b43 |
998 | |
055fd3a9 |
999 | You can change options from F<.perldb> by using calls like this one; |
36477c24 |
1000 | |
1001 | parse_options("NonStop=1 LineInfo=db.out AutoTrace=1 frame=2"); |
1002 | |
055fd3a9 |
1003 | The code is executed in the package C<DB>. Note that F<.perldb> is |
774d564b |
1004 | processed before processing C<PERLDB_OPTS>. If F<.perldb> defines the |
055fd3a9 |
1005 | subroutine C<afterinit>, that function is called after debugger |
774d564b |
1006 | initialization ends. F<.perldb> may be contained in the current |
055fd3a9 |
1007 | directory, or in the home directory. Because this file is sourced |
1008 | in by Perl and may contain arbitrary commands, for security reasons, |
1009 | it must be owned by the superuser or the current user, and writable |
1010 | by no one but its owner. |
36477c24 |
1011 | |
bea98532 |
1012 | You can mock TTY input to debugger by adding arbitrary commands to |
1013 | @DB::typeahead. For example, your F<.perldb> file might contain: |
1014 | |
1015 | sub afterinit { push @DB::typeahead, "b 4", "b 6"; } |
1016 | |
1017 | Which would attempt to set breakpoints on lines 4 and 6 immediately |
d7f8936a |
1018 | after debugger initialization. Note that @DB::typeahead is not a supported |
bea98532 |
1019 | interface and is subject to change in future releases. |
1020 | |
055fd3a9 |
1021 | If you want to modify the debugger, copy F<perl5db.pl> from the |
1022 | Perl library to another name and hack it to your heart's content. |
1023 | You'll then want to set your C<PERL5DB> environment variable to say |
1024 | something like this: |
36477c24 |
1025 | |
1026 | BEGIN { require "myperl5db.pl" } |
1027 | |
055fd3a9 |
1028 | As a last resort, you could also use C<PERL5DB> to customize the debugger |
1029 | by directly setting internal variables or calling debugger functions. |
1030 | |
1031 | Note that any variables and functions that are not documented in |
1032 | this document (or in L<perldebguts>) are considered for internal |
1033 | use only, and as such are subject to change without notice. |
36477c24 |
1034 | |
4e1d3b43 |
1035 | =head2 Readline Support |
1036 | |
055fd3a9 |
1037 | As shipped, the only command-line history supplied is a simplistic one |
4e1d3b43 |
1038 | that checks for leading exclamation points. However, if you install |
1039 | the Term::ReadKey and Term::ReadLine modules from CPAN, you will |
1040 | have full editing capabilities much like GNU I<readline>(3) provides. |
1041 | Look for these in the F<modules/by-module/Term> directory on CPAN. |
055fd3a9 |
1042 | These do not support normal B<vi> command-line editing, however. |
4e1d3b43 |
1043 | |
055fd3a9 |
1044 | A rudimentary command-line completion is also available. |
e7ea3e70 |
1045 | Unfortunately, the names of lexical variables are not available for |
1046 | completion. |
1047 | |
4e1d3b43 |
1048 | =head2 Editor Support for Debugging |
1049 | |
055fd3a9 |
1050 | If you have the FSF's version of B<emacs> installed on your system, |
1051 | it can interact with the Perl debugger to provide an integrated |
1052 | software development environment reminiscent of its interactions |
1053 | with C debuggers. |
4e1d3b43 |
1054 | |
055fd3a9 |
1055 | Perl comes with a start file for making B<emacs> act like a |
1056 | syntax-directed editor that understands (some of) Perl's syntax. |
1057 | Look in the I<emacs> directory of the Perl source distribution. |
4e1d3b43 |
1058 | |
055fd3a9 |
1059 | A similar setup by Tom Christiansen for interacting with any |
1060 | vendor-shipped B<vi> and the X11 window system is also available. |
1061 | This works similarly to the integrated multiwindow support that |
1062 | B<emacs> provides, where the debugger drives the editor. At the |
1063 | time of this writing, however, that tool's eventual location in the |
1064 | Perl distribution was uncertain. |
4e1d3b43 |
1065 | |
055fd3a9 |
1066 | Users of B<vi> should also look into B<vim> and B<gvim>, the mousey |
2e8f3c35 |
1067 | and windy version, for coloring of Perl keywords. |
a0d0e21e |
1068 | |
055fd3a9 |
1069 | Note that only perl can truly parse Perl, so all such CASE tools |
1070 | fall somewhat short of the mark, especially if you don't program |
1071 | your Perl as a C programmer might. |
e7ea3e70 |
1072 | |
055fd3a9 |
1073 | =head2 The Perl Profiler |
d74e8afc |
1074 | X<profile> X<profiling> X<profiler> |
e7ea3e70 |
1075 | |
055fd3a9 |
1076 | If you wish to supply an alternative debugger for Perl to run, just |
1077 | invoke your script with a colon and a package argument given to the |
1078 | B<-d> flag. The most popular alternative debuggers for Perl is the |
1079 | Perl profiler. Devel::DProf is now included with the standard Perl |
1080 | distribution. To profile your Perl program in the file F<mycode.pl>, |
1081 | just type: |
36477c24 |
1082 | |
055fd3a9 |
1083 | $ perl -d:DProf mycode.pl |
36477c24 |
1084 | |
055fd3a9 |
1085 | When the script terminates the profiler will dump the profile |
1086 | information to a file called F<tmon.out>. A tool like B<dprofpp>, |
1087 | also supplied with the standard Perl distribution, can be used to |
1088 | interpret the information in that profile. |
36477c24 |
1089 | |
055fd3a9 |
1090 | =head1 Debugging regular expressions |
d74e8afc |
1091 | X<regular expression, debugging> |
1092 | X<regex, debugging> X<regexp, debugging> |
36477c24 |
1093 | |
3d555cb8 |
1094 | C<use re 'debug'> enables you to see the gory details of how the Perl |
1095 | regular expression engine works. In order to understand this typically |
1096 | voluminous output, one must not only have some idea about how regular |
1097 | expression matching works in general, but also know how Perl's regular |
1098 | expressions are internally compiled into an automaton. These matters |
1099 | are explored in some detail in |
055fd3a9 |
1100 | L<perldebguts/"Debugging regular expressions">. |
36477c24 |
1101 | |
055fd3a9 |
1102 | =head1 Debugging memory usage |
d74e8afc |
1103 | X<memory usage> |
36477c24 |
1104 | |
055fd3a9 |
1105 | Perl contains internal support for reporting its own memory usage, |
1106 | but this is a fairly advanced concept that requires some understanding |
1107 | of how memory allocation works. |
1108 | See L<perldebguts/"Debugging Perl memory usage"> for the details. |
36477c24 |
1109 | |
055fd3a9 |
1110 | =head1 SEE ALSO |
a0d0e21e |
1111 | |
1112 | You did try the B<-w> switch, didn't you? |
1113 | |
f6b3c421 |
1114 | L<perldebtut>, |
055fd3a9 |
1115 | L<perldebguts>, |
1116 | L<re>, |
1117 | L<DB>, |
fe854a6f |
1118 | L<Devel::DProf>, |
055fd3a9 |
1119 | L<dprofpp>, |
1120 | L<Dumpvalue>, |
1121 | and |
1122 | L<perlrun>. |
a0d0e21e |
1123 | |
fa3aa65a |
1124 | When debugging a script that uses #! and is thus normally found in |
1125 | $PATH, the -S option causes perl to search $PATH for it, so you don't |
66a1b24b |
1126 | have to type the path or C<which $scriptname>. |
fa3aa65a |
1127 | |
1128 | $ perl -Sd foo.pl |
1129 | |
055fd3a9 |
1130 | =head1 BUGS |
1131 | |
1132 | You cannot get stack frame information or in any fashion debug functions |
1133 | that were not compiled by Perl, such as those from C or C++ extensions. |
a0d0e21e |
1134 | |
c997b287 |
1135 | If you alter your @_ arguments in a subroutine (such as with C<shift> |
6edf2346 |
1136 | or C<pop>), the stack backtrace will not show the original values. |
c997b287 |
1137 | |
1138 | The debugger does not currently work in conjunction with the B<-W> |
1139 | command-line switch, because it itself is not free of warnings. |
4c82ae22 |
1140 | |
1141 | If you're in a slow syscall (like C<wait>ing, C<accept>ing, or C<read>ing |
1142 | from your keyboard or a socket) and haven't set up your own C<$SIG{INT}> |
1143 | handler, then you won't be able to CTRL-C your way back to the debugger, |
1144 | because the debugger's own C<$SIG{INT}> handler doesn't understand that |
1145 | it needs to raise an exception to longjmp(3) out of slow syscalls. |