## open

`open filename`

Opens `filename`, which should be the name of a GrADS data descriptor file, also called a control file.

### Usage Notes

1. The standard file extension for Grads data descriptor files is `.ctl`. Provided you adhere to this standard, there is no need to type the extension `.ctl` when issuing the `open` command.

2. You will need to open at least one data-descriptor file before you can enter other GrADS commands.

3. You can open more than one data-descriptor file. Each file is numbered according to the order in which it was opened.

### Examples

`open jandata.1966
open jandata.1966.ctl`

Both of these commands will have the same effect -- opening the GrADS data descriptor file `"jandata.1966.ctl"`.