removing last character

Hi,

I have a file that has data something like below:

A
B
C
D
.....
......
.....and so on

I am trying to bring it in one line with comma delimited something like below :

A,B,C,D

I tried the something below in the code section:

cat File.txt | tr '\n' ','

but getting a comma at the line something like below, which I don't want:

A,B,C,D, --> I don't want comma at the end of the line.

Try this:

paste -sd, infile