1Data::Dump(3) User Contributed Perl Documentation Data::Dump(3)
2
6 Data::Dump - Pretty printing of data structures
7
9 use Data::Dump qw(dump);
10 $str = dump(@list);
12 @copy_of_list = eval $str;
13 # or use it for easy debug printout
15 use Data::Dump; dd localtime;
16
18 This module provide a few functions that traverse their argument and
19 produces a string as its result. The string contains Perl code that,
20 when "eval"ed, produces a deep copy of the original arguments.
21 The main feature of the module is that it strives to produce output
23 that is easy to read. Example:
24 @a = (1, [2, 3], {4 => 5});
26 dump(@a);
27 Produces:
29 "(1, [2, 3], { 4 => 5 })"
31 If you dump just a little data, it is output on a single line. If you
33 dump data that is more complex or there is a lot of it, line breaks are
34 automatically added to keep it easy to read.
35 The following functions are provided (only the dd* functions are
37 exported by default):
38 dump( ... )
40 pp( ... )
41 Returns a string containing a Perl expression. If you pass this
42 string to Perl's built-in eval() function it should return a copy
43 of the arguments you passed to dump().
44 If you call the function with multiple arguments then the output
46 will be wrapped in parenthesis "( ..., ... )". If you call the
47 function with a single argument the output will not have the
48 wrapping. If you call the function with a single scalar (non-
49 reference) argument it will just return the scalar quoted if
50 needed, but never break it into multiple lines. If you pass
51 multiple arguments or references to arrays of hashes then the
52 return value might contain line breaks to format it for easier
53 reading. The returned string will never be "\n" terminated, even
54 if contains multiple lines. This allows code like this to place
55 the semicolon in the expected place:
56 print '$obj = ', dump($obj), ";\n";
58 If dump() is called in void context, then the dump is printed on
60 STDERR and then "\n" terminated. You might find this useful for
61 quick debug printouts, but the dd*() functions might be better
62 alternatives for this.
63 There is no difference between dump() and pp(), except that dump()
65 shares its name with a not-so-useful perl builtin. Because of this
66 some might want to avoid using that name.
67 quote( $string )
69 Returns a quoted version of the provided string.
70 It differs from "dump($string)" in that it will quote even numbers
72 and not try to come up with clever expressions that might shorten
73 the output. If a non-scalar argument is provided then it's just
74 stringified instead of traversed.
75 dd( ... )
77 ddx( ... )
78 These functions will call dump() on their argument and print the
79 result to STDOUT (actually, it's the currently selected output
80 handle, but STDOUT is the default for that).
81 The difference between them is only that ddx() will prefix the
83 lines it prints with "# " and mark the first line with the file and
84 line number where it was called. This is meant to be useful for
85 debug printouts of state within programs.
86 dumpf( ..., \&filter )
88 Short hand for calling the dump_filtered() function of
89 Data::Dump::Filtered. This works like dump(), but the last
90 argument should be a filter callback function. As objects are
91 visited the filter callback is invoked and it can modify how the
92 objects are dumped.
93
95 There are a few global variables that can be set to modify the output
96 generated by the dump functions. It's wise to localize the setting of
97 these.
98 $Data::Dump::INDENT
100 This holds the string that's used for indenting multiline data
101 structures. It's default value is " " (two spaces). Set it to ""
102 to suppress indentation. Setting it to "| " makes for nice visuals
103 even if the dump output then fails to be valid Perl.
104 $Data::Dump::TRY_BASE64
106 How long must a binary string be before we try to use the base64
107 encoding for the dump output. The default is 50. Set it to 0 to
108 disable base64 dumps.
109
111 Code references will be dumped as "sub { ... }". Thus, "eval"ing them
112 will not reproduce the original routine. The "..."-operator used will
113 also require perl-5.12 or better to be evaled.
114 If you forget to explicitly import the "dump" function, your code will
116 core dump. That's because you just called the builtin "dump" function
117 by accident, which intentionally dumps core. Because of this you can
118 also import the same function as "pp", mnemonic for "pretty-print".
119
121 The "Data::Dump" module grew out of frustration with Sarathy's in-most-
122 cases-excellent "Data::Dumper". Basic ideas and some code are shared
123 with Sarathy's module.
124 The "Data::Dump" module provides a much simpler interface than
126 "Data::Dumper". No OO interface is available and there are fewer
127 configuration options to worry about. The other benefit is that the
128 dump produced does not try to set any variables. It only returns what
129 is needed to produce a copy of the arguments. This means that
130 "dump("foo")" simply returns '"foo"', and "dump(1..3)" simply returns
131 '(1, 2, 3)'.
132
134 Data::Dump::Filtered, Data::Dump::Trace, Data::Dumper, JSON, Storable
135
137 The "Data::Dump" module is written by Gisle Aas <gisle@aas.no>, based
138 on "Data::Dumper" by Gurusamy Sarathy <gsar@umich.edu>.
139 Copyright 1998-2010 Gisle Aas.
141 Copyright 1996-1998 Gurusamy Sarathy.
142 This library is free software; you can redistribute it and/or modify it
144 under the same terms as Perl itself.
145perl v5.30.1 2020-01-29 Data::Dump(3)