Most of the development of your CGI script should be done in this mode of execution. To get offline execution, you simply run the CGI script as a normal Perl script on, for example, an IBM workstation. Suppose you execute the script add.cgi. You will get the following prompt:
(offline mode: enter name=value pairs on standard input)
If you hit 
at this point, the script should produce the HTML
corresponding to the form that the user will use to enter input. As
long as you use the routines header(), start_html(),
start_form(), end_form(), and end_html() with HTML
emitting functions placed between start_html() and
end_html() and HTML form widgets only placed between
start_form() and end_form(), the HTML produced should be
valid (if not aesthetically pleasing when printed). However, this is
a good way to check for run-time warnings and other problems.
Continuing the above example, a would give us
Content-type: text/html <!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN"> <HTML><HEAD><TITLE>Add Me</TITLE> </HEAD><BODY><H1>Add Me</H1><HR><FORM METHOD="POST" ENCTYPE="application/x-www-form-urlencoded"> <P>First Number: <INPUT TYPE="text" NAME="field1" VALUE=""></P> <P>Second Number: <INPUT TYPE="text" NAME="field2" VALUE=""></P> <P><INPUT TYPE="submit" NAME="add" VALUE="add"> <INPUT TYPE="reset" VALUE="clear"></P> </FORM><HR></BODY></HTML>
To make your script execute as if it received user input, enter the
-NAME that you gave each widget followed by an equals sign and
a test value you would like it to have. Note that giving a widget a
name containing spaces will work in online mode but will be a problem
in offline mode. If the value has spaces in it, like hello
there, it should be enclosed in quotes. When you are done with the
list, type . For add.cgi, we could enter
field1=3 
field2=4
The script would emit:
Content-type: text/html <!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML//EN"> <HTML><HEAD><TITLE>Add Me</TITLE> </HEAD><BODY><H1>Add Me</H1><P>3 + 4 = <B>7</B> </P></BODY></HTML>Again, it could also generate Perl warnings or programmer-defined error messages.
What if you have a widget that allows the user to select several
values to return to the CGI script (for example, a
checkbox_group)? Then you simply repeat the
widget-name-equals-value combination for each value:
operating_systems=AIX
operating_systems='Sun OS'
Instead of typing in the data each time, you can create several files of the proper format and then run the script by redirecting standard input to come from a file. For example, if we have a file called input.batch, with the following contents:
N03=yes G11=yes QN03=1 QG11=3 name="Louis Ziantz" address="CS Dept, RPI" city=Troy state=NY zip=12180 comm_stat=Noncommercial username=ziantzl password=youkilledkenny password2=youkilledkenny
we can run cart.cgi as cart.cgi < input.batch.