Shared Hosting CGI Setup
CGI on shared hosting: cgi-bin, permissions, and getting your first script running
How do I run a CGI script on shared hosting?
On most shared hosts, CGI scripts must be placed in the cgi-bin directory (or a subdirectory of it), set to execute permissions (chmod 755), and begin with a shebang line pointing to the correct interpreter path on that host. The URL to reach the script is typically https://yourdomain.com/cgi-bin/scriptname.cgi. Errors nearly always fall into three categories: wrong interpreter path, wrong permissions, or output printed before the Content-Type header.
Finding the cgi-bin directory
Most traditional cPanel-based shared hosts create a cgi-bin directory at the root of your hosting account, accessible via FTP at /home/username/public_html/cgi-bin or similar. The URL path is /cgi-bin/ on your domain. Some hosts configure the entire account home to allow CGI, others restrict it to specific directories. Log into your hosting control panel and look for a CGI or Perl section in the documentation, or ask your host's support.
Some hosts also allow you to create additional CGI-enabled directories using a .htaccess file with Options +ExecCGI and AddHandler cgi-script .cgi .pl. This lets you put CGI scripts in a more logical URL path rather than under /cgi-bin. Whether this is permitted depends on the host's server configuration; not all allow .htaccess overrides of ExecCGI.
File permissions and the shebang
CGI scripts need two things to execute: the correct shebang and execute permission. The shebang must point to the exact path of the interpreter on your host. Common paths are /usr/bin/perl, /usr/local/bin/perl, /usr/bin/python3, /usr/bin/env perl, and /usr/bin/env python3. Run 'which perl' or 'which python3' via SSH to find the right path, or ask your host. A wrong shebang path causes a 500 error that can look identical to a syntax error or permission problem.
Permissions must be exactly 755 (rwxr-xr-x) for CGI scripts on most hosts. 777 (world-writable) is often rejected as a security risk; 644 (no execute bit) means the server will not execute the script. Set permissions after uploading via your FTP client or with chmod 755 scriptname.cgi via SSH.
Testing before you go live
The fastest way to debug a CGI script on shared hosting is via SSH. Run perl -c scriptname.cgi to check for syntax errors without the web server involved. Then set the minimum required environment variables and run the script directly: REQUEST_METHOD=GET QUERY_STRING='' perl scriptname.cgi. You will see exactly what the script would print as an HTTP response, making header and output errors obvious without needing to check web server logs.
If SSH is not available, add use CGI::Carp qw(fatalsToBrowser) (Perl) or import cgitb; cgitb.enable() (Python) at the top of the script during debugging to redirect fatal errors to the browser. Remove these before leaving the script in production, since they expose internal paths and error details to visitors.
What to know
Key points
- Find the correct interpreter path with 'which perl' or 'which python3'. A wrong shebang path causes a 500 error that looks just like other errors; verify the exact path first.
- Set permissions to exactly 755. 644 lacks the execute bit; 777 is often rejected; 755 is the standard for CGI scripts.
- Test via SSH before troubleshooting through the browser. Running the script directly shows you the raw output and makes header problems obvious.
- Ask your host if .htaccess ExecCGI is permitted. Enabling CGI outside cgi-bin via .htaccess requires the host to allow AllowOverride Options.
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