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