General Programming Tips to Avoid Bugs

• First, have your program well laid out in pseudocode
• Make sure you put in enough comments in your code to explain what you are doing
• Design your program in sections! When you write a function, make sure it works before you go on to the next one. Don't let mistakes pile onto each other.
• Logic errors are the worst. You've done the code right, but you actually told it to do the wrong thing. Work through your code, line by line, and writed down what you would expect at each line.
• If you have a tricky error, add a print statement at each point you define a new variable or do a calculation so you can see what is happening to your data at each step. You can remove them once you get everything working. (ie in Javascript just add a bunch of "document.write(variablename)" at the appropriate places.

PHP Tips

• Have good comments to keep track of what you are doing
• Use print statements to see what a variable is actually being set to at each step in your program (remove or comment them out later)
• Log into the server and check out the server logs

Javascript Tips

First off, in Javascript, type "javascript:" in the "location" bar of netscape to bring up the error console.

• NOTE: The error you get may not be the actual problem, but a symptom. Figure out what calls that part of your program and look for missing pieces of mispellings.
• If it says "unterminated string literal" you have either forgotton a set of quotes, or one of your "document.write" statements has wrapped in a bad place and you need to use a \ to escape it
• If it says "functionname undefined" where functionname is one of your functions, check to make sure that you are not calling the function from the head of the document when the function is down in the body. Always have your function definitions ABOVE where your code actually calls the function.
• Always check spellings and case on variable and function names

Perl Debugging Tips

• If you are getting more lines of output than you want, you probably forgot to chomp off the new line characters from input you got from the user via
• The first line with the "shebang" in it #! points to the wrong directory for perl (Or you forgot the leading / after the #!)
• Also remember the leading "/" in #!/usr/local/bin/perl -wT (Or whatever the path is to your perl program, check out Getting started with Perl for more info.
• You forgot to set the file executable (on unix systems) so go chmod a+x filename.pl
• To test just a normal perl program, go ./filename.pl when you are in the same directory as the file
• Remember, on many web servers, the ending must be .cgi instead of .pl
• To test a CGI program at the prompt, go into cgi-bin and type
  ./progname.cgi fieldname1="value" fieldname2="value" etc
  where progname is the name of your cgi program, and fieldname1 is the "name" from your first form element, and the "value" is what you want it to equal.
• Now, eventually you'll actually want to test this on a real form, so where do the errors show up? In the case of the apache web server, it should be in a file called error_log, so you can try one of the following to find your errors:
  • tail -f /home/web/logs/error_log | grep username (if needed, you can open in a seperate putty window and it will scroll YOUR error messages along)
  • To get back to the command line, hit ctrl c
• Make sure you know what your form is passing to your script!
• Checkboxes give a name=on result (say you had the name=carcolor, then you'd get carcolor=on) unless you specify a value for them.
• When not checked, checkboxes do not send anything. There would be no carcolor=off....it just wouldn't show up at all in the output.