Passing IPython variables as arguments to bash commands

How do I execute a bash command from Ipython/Jupyter notebook passing the value of a python variable as an argument like in this example:

py_var="foo"
!grep py_var bar.txt

(obviously I want to grep for foo and not the literal string py_var)

Simple case

Prefix your variable names with a $.

For example, say you want to copy a file file1 to a path stored in a python variable named dir_path:

dir_path = "/home/foo/bar"
!cp file1 $dir_path

• Note: If using Bash, keep in mind that some strings need to be quoted:

  !cp file1 "$dir_path"
  

General case

Wrap your variable names in {..}:

dir_path = "/home/foo/bar"
!cp file1 {dir_path}

Its behaviour is more predictable and powerful than $... E.g. if you want to concatenate another string sub_dir to your path, $ can't do that, while with {..} you can do:

!cp file1 {dir_path + sub_dir}

• Note: Again for Bash, quotes:

  !cp file1 "{dir_path}"
  

  !cp file1 "{dir_path + sub_dir}"
  

Raw strings

For a related discussion on the use of raw strings (prefixed with r) to pass the variables, see Passing Ipython variables as string arguments to shell command