How to Find Files Using Regular Expressions in Ubuntu (find -regex)

The Complex Match Requirement

In Ubuntu Linux, the standard -name flag in the find command is limited to simple wildcard matching (like *.log or backup_*.tar.gz). However, if you are a system administrator auditing a server for complex file patterns—such as searching for temporary files that end in exactly three numbers, or locating all PHP files that contain a specific alphanumeric hex code in their filename—simple wildcards are mathematically insufficient. You must instruct the search engine to parse the directory tree using strict Regular Expressions (Regex).

Using the find Command with -regex

The Linux find command utilizes the -regex flag to evaluate the entire file path against a defined regular expression pattern.

1. Open your Terminal application (Ctrl + Alt + T) or log into your server via SSH.
2. To search the /var/www/ directory for any files that end in .php followed by exactly two digits (e.g., script.php12), type the following command exactly:
3. find /var/www/ -regex ".*\.php[0-9][0-9]"
4. Press Enter.

Full Path Evaluation

Unlike -name which only looks at the final file name, the -regex flag evaluates the entire absolute path (e.g., /var/www/html/script.php12). This is why the regular expression must begin with .* to account for the preceding directory structure. By default, find utilizes Emacs regular expression syntax. This powerful command is an absolute necessity for developers writing automated cleanup scripts that need to surgically target highly specific, machine-generated file patterns while ignoring standard files.