issue on ssh command in ksh shell

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http://www.unix.com – Hi guru, I'm making crazy cause an issue on a ksh shell I made. In this shell I want to execute unix command on a remote machine using an ssh connection like ssh user@host 'command'..... The command is very simply, is an ls on a remote directory but it give me an unexpected result. The command is built using a variable: ssh user@host 'ls ${var}' where var is a concatenation of others variables. Whith this command I want to retrieve a specific file with a specific format like 20120917_filename.csv.gz So the first variable contain the path in which I looking for the file, the second contai (HowTos)