The base64 command wraps its output every 76 characters by default. This is because of its original use which was to encode binary files to include in emails.

The base64 command wraps its output every 76 characters by default. This is because of its original use which was to encode binary files to include in emails. Very long lines in emails don't work well. See the precursor to base64 which is the uuencode command which you probably have installed too if you have the base64 command. base64 is a better, standardised version of uuencode. Use --wrap=0 to disable.