Debugging
Debugging
If you are running the script from the command line or
in the perl debugger, you can pass the script a list of keywords or
parameter=value pairs on the command line or from standard input (you don't have
to worry about tricking your script into reading from environment variables).
You can pass keywords like this:
my_script.pl keyword1 keyword2
keyword3
or this:
my_script.pl
keyword1+keyword2+keyword3
or this:
my_script.pl name1=value1
name2=value2
or this:
my_script.pl
name1=value1&name2=value2
If you pass the -debug pragma to CGI.pm, you can
send CGI name-value pairs as newline-delimited parameters on standard input:
% my_script.pl
first_name=fred
last_name=flintstone
occupation='granite miner'
^D
When debugging, you can use quotation marks and the
backslash character to escape spaces and other funny characters in exactly the
way you would in the shell (which isn't surprising since CGI.pm uses
"shellwords.pl" internally). This lets you do this sort of thing:
my_script.pl 'name 1=I am a long value' name\ 2=two\
words
If you run a script that uses CGI.pm from the command
line and fail to provide it with any arguments, it will print out the line
(offline mode: enter name=value pairs on standard
input)
then appear to hang. In fact, the library is waiting for
you to give it some parameters to process on its standard input. If you want to
give it some parameters, enter them as shown above, then indicate that you're
finished with input by pressing ^D (^Z on NT/DOS systems). If you don't want to
give CGI.pm parameters, just press ^D.
You can suppress this behavior in any of the following
ways:
1. Call the script with an empty parameter.
Example:
my_script.pl ''
2. Redirect standard input from /dev/null or an empty
file.
Example:
my_script.pl </dev/null
3. Include "-no_debug" in the list of symbols to import
on the "use" line.
Example:
use CGI qw/:standard -no_debug/;
Dumping Out All The Name/Value
Pairs
The Dump() method produces a string consisting of
all the query's name/value pairs formatted nicely as a nested list. This is
useful for debugging purposes:
print $query->Dump
Produces something that looks like this:
<UL>
<LI>name1
<UL>
<LI>value1
<LI>value2
</UL>
<LI>name2
<UL>
<LI>value1
</UL>
</UL>
You can achieve the same effect by incorporating the CGI
object directly into a string, as in:
print "<H2>Current
Contents:</H2>\n$query\n";
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