A very common need in SSIS is to check to see if a file exist before you run what could be a very long process in your package.  There are no native tasks inside SSIS that can do this check but you can accomplish this using a Script Task.  Here are the steps to check to see if a file exist.  To view this blog with screenshots visit my regular blog at http://blogs.pragmaticworks.com/devin_knight/.

1.  Setup two variables.  The variable named strFileLocation has a string data type with the value being the location of the file I want to check for.  The variable bolFileExists has a boolean data type with the value changing based on whether the file exist or not.  If the file is found the value will be changed to True otherwise it stays False.

2.  Use a Script Task in the Control Flow and set the ReadOnlyVariables to use the strFileLocation variable and the ReadWriteVariables to use the bolFileExists variable then select Edit Script.

3.  There are two methods for writing this script.  The first method you must first add the namespace System.IO.  The second method does not require this.

4.  Scroll down the editor until you find the green commented out text that says Add your code here.  Replace that with the following code then save and close the editor :

Dts.Variables("bolFileExists").Value = File.Exists(Dts.Variables("strFileLocation").Value)

The second option for the script is (Remember this option is not using the Imports System.IO step) :

Dts.Variables("bolFileExists").Value = My.Computer.FileSystem.FileExists(Dts.Variables("strFileLocation").Value) 

5.  Now that you have the script done you can use things more familiar to you in SSIS like precedence constraints with expressions to get the desired results.  Connect the completed Script Task to a path that you want the package to move if the file does exist.  Open the precedence constraints editor by double clicking on the line. change the Evaluation operation to Expression and Constraint and add the expression @bolFileExists==True.  Remember the double equals is a comparison.  If it was a single equal sign it would be trying to set the value of the variable to True.  Click OK once complete.  If you want a path for if the file is not found then follow the same steps with the precedence constraint but the expression should be @bolFileExists==False.

I’m using script tasks just as placeholders here for how the rest of the package may look.  If my file did exist it would go down the left path.  If it did not exist my package flow would go right.