X3270INPUT environment variable

The  environment variable is passed from the emulator to a program run by the Script action. It indicates the file descriptor of a pipe used to send actions to the emulator to execute. The results are reported on the file descriptor of a pipe defined by the X3270OUTPUT environment variable. The s3270 protocol defines the format of the data sent on these pipes.

These two variables are used only on POSIX systems.

Example
Send the Enter action from a bash script. echo >&$X3270INPUT "Enter"