Final answer:
To pass an IPython variable to the shell, use the exclamation mark followed by the variable name. This allows you to execute shell commands using the value of the variable.
Step-by-step explanation:
To pass an IPython variable to the shell, you can use the ! (exclamation mark) followed by the variable name. This allows you to execute shell commands using the value of the variable.
For example, if you have a variable named filename containing the name of a file, you can pass it to the shell like this:
!cat $filename
This will execute the cat command in the shell, displaying the contents of the file whose name is stored in the filename variable.
$ filename = 'data.txt'
$ !cat {filename}
Where cat is the shell command that will be executed with the content of filename passed to it. This feature of IPython makes it convenient to interact with the shell without leaving the IPython interface.