Shell commands in IPython

The IPython Notebook allows simple UNIX/Linux commands to be executed in a single input cell. There are no limits but when using, please keep in mind that in contrast to a regular UNIX/Linux shell, start each shell command with a !, for example !ls for the command ls (see below for further explanations about the command). Furthermore, each shell command is executed in its own subshell. For this reason, the results of previous shell commands are not available to you.

To begin with, the command ls lists the files in the current working directory. The output is shown below the input cell, and lists the single file shell.ipynb:

!ls

debugging.ipynb                         mypackage
debugging.ipynb.license                 myscript.py
display.ipynb                           shell.ipynb
display.ipynb.license                   shell.ipynb.license
examples.ipynb                          start.rst
examples.ipynb.license                  tab-completion-for-anything.png
extensions.rst                          tab-completion-for-anything.png.license
importing.ipynb                         tab-completion-for-modules.png
importing.ipynb.license                 tab-completion-for-modules.png.license
index.rst                               tab-completion-for-objects.png
magics.ipynb                            tab-completion-for-objects.png.license
magics.ipynb.license                    unix-shell

The command !pwd displays the path to working directory:

!pwd

/Users/veit/cusy/trn/Python4DataScience/docs/workspace/ipython

The command !echo outputs text given as parameter to the echo command. The example below demonstrates how to print Hello world:

!echo "Hello world!"

Hello world!

Passing values to and from the shell

There is a clever way through which you can access the output of a UNIX/Linux command as a variable in Python. Assign the output of a UNIX/Linux command to a variable as follows:

contents = !ls

Here the Python variable contents has been assigned the output of the command ls. As a result, contents is a list, where each list element corresponds to a line in the output. With the print command you output the list contents:

print(contents)

['debugging.ipynb', 'debugging.ipynb.license', 'display.ipynb', 'display.ipynb.license', 'examples.ipynb', 'examples.ipynb.license', 'extensions.rst', 'importing.ipynb', 'importing.ipynb.license', 'index.rst', 'magics.ipynb', 'magics.ipynb.license', '\x1b[34mmypackage\x1b[m\x1b[m', 'myscript.py', 'shell.ipynb', 'shell.ipynb.license', 'start.rst', '\x1b[31mtab-completion-for-anything.png\x1b[m\x1b[m', 'tab-completion-for-anything.png.license', '\x1b[31mtab-completion-for-modules.png\x1b[m\x1b[m', 'tab-completion-for-modules.png.license', '\x1b[31mtab-completion-for-objects.png\x1b[m\x1b[m', 'tab-completion-for-objects.png.license', '\x1b[34munix-shell\x1b[m\x1b[m']

You will see the same result below when executing the pwd command. The current directory is stored in the variable directory:

directory = !pwd

print(directory)

['/Users/veit/cusy/trn/Python4DataScience/docs/workspace/ipython']