How Actions reads files
Actions guesses some things about the files it imports from S3 (or elsewhere) base on the filename.
File Compression
Actions can read files compressed with gzip or bzip2 as well as zip archives. In the case of zip archives, Actions will read every file in the archive.
zip files will be read with zip compression
.gz or .gz2 files will be read with gzip compression
.bz or bz2 will be read with bzip2 compression
File Delimiters
Actions guesses the file delimiter based on its file extension.
.csv files are treated as comma separated
.txt or .tsv files are treated as tab separated
.psv files are treated as pipe (pipe: |) separated
.tilde files are treated as tilde (tilde: ~) separated
Anything else defaults to comma separated
A Note About Zip Archives
The combination of these two things can create a bit of wonkiness with zip archives, so the suggested format there would be {whatever}.csv.zip. Include the .csv (or whatever other extensions) ensure that actions guess the correct delimited for all files in the archive.
Compression Encouraged
Using a compressed file is strongly encouraged as it can speed up the time it takes actions to download the file from S3 or elsewhere.