The feasibility of this depends totally on the nature of the CGI script you're wanting to call by hand. CGI scripts by their nature expect to be called from a web server, expect their arguments to provided per CGI spec, and will provide CGI output. The script.pl?argument construct is a web/CGI thing, but since you're trying to call your script via standard system() methods, CGI methods don't apply. Fortunately, the "GET" method you're using makes it easy:

system("./1.pl filename.txt");      # to stdout, or:
my $output = `./1.pl filename.txt`  # in $output
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A security note: If, instead of using "filename.txt", you use a user-provided variable, make SURE your script uses taint-checking (-T argument, see perlsec) and un-taint the variable smartly before attempting to use it, or someone can easily put in a filename of "/etc/passwd" or "some.file;rm -rf /etc/httpd|", for example.

Since the script is a CGI script, its output will contain CGI headers. If this is OK, great. Otherwise, you will need to strip them out.

Perhaps you should consider an ASP technique for running a CGI script "within" the context of a page (with SSI this is called a "virtual include").

Hope this helps.