Check the size of the file on different server

Hello,
I have two servers A and B, My script is written on Server A. I am picking up the file say "abc.txt" from Server B using sftp command and putting it in a directory at Server A.

Now the catch is, If the file size of "abc.txt" is greater thn the available size on Server A, thn an email should be sent with the error msg.
question::
1) How to check the size of the file "abc.txt" from server A. Also, I tried ls -ltr abc.txt on ftp prompt but its not working

Please Help
Thanks in advance

Double post. Continued here: