To concatenate all files in a directory using the cat command on a UNIX system, you can use a wildcard character to match all files in the directory, then redirect the output to a new file. The command would look something like this:
cat /path/to/directory/* > combined_file.txt
This command will concatenate all files in the specified directory and output the result to a new file named combined_file.txt. Note that the order in which the files are concatenated may not be the same as the order in which they appear in the directory.
If you want to concatenate only certain types of files, you can use a more specific wildcard pattern, such as:
cat /path/to/directory/*.txt > combined_file.txt
This will only concatenate files with a .txt extension. You can use any other pattern that matches the files you want to concatenate.