Odd results on base64 operations

I am having weird output on base64 operations. I have something I want to programmatically download, and found that the links contains base64 encoded data ({date}.zip. This is evidenced by the following:

> echo "MjAyMS0wMS0xMy56aXA="  | base64 --decode
2021-01-13.zip%

If I pipe that back into base64, I get the same result back:

> echo "MjAyMS0wMS0xMy56aXA="  | base64 --decode | base64
MjAyMS0wMS0xMy56aXA=

However, if I pass the decoded string directly to base64, I get a different result:

> echo "2021-01-13.zip"  | base64
MjAyMS0wMS0xMy56aXAK

Curious as to why this is happening, and how I can resolve.

Thanks!

Solution 1:

Compare the output of these two commands:

echo "MjAyMS0wMS0xMy56aXA="  | base64 --decode | od -c
echo "2021-01-13.zip" | od -c

You will see there is no newline character in what base64 --decode prints (because the string you start with apparently does not encode a newline character). There is a newline character in what echo prints (because this is how echo works). Now try this:

echo -n "2021-01-13.zip"  | base64

Or better:

printf '%s' "2021-01-13.zip"  | base64

Solution 2:

Echo adds by default a trailing end of line character.

Try without adding the end of line:

> echo -n "2021-01-13.zip"  | base64
MjAyMS0wMS0xMy56aXA=