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