UNIX script to check file and start the informatica server

Hi Rockers,
I hope u r dng good one. I have a one question is in unix with informatica . I need a unix script to check whether particular file exists in the folder , If it means we have a informatica server , so we can start the informatica server by accessing that file. Every week we have get the files from source system with same name as 'file1'. I need to run the scripts to check whether files come or not , will start the sever , else it will be dispalyed "file not found". u can write a shell script by using date or filename... Please help me.:o

Regards
guru

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