Cat the first file returned by ls command

Here we use ls -1 to get a list of the directory contents, pipe it to head -n 1 to get one line, and pipe that to xargs cat.

ls -1 | head -n 1 | xargs cat

This might fail if the argument piped to cat is a directory. You could use a more convoluted strategy to prevent this scenario.

ls -p | grep -v / | head -n 1 | xargs cat

Use the ls -t flag to sort the directory by timestamp.

ls -pt | grep -v / | head -n 1 | xargs cat