Reporting new USB storage devices on Linux and macOS with Python

Synopsis:

I wanted something for macOS (and Linux; maybe eventually Windows) that would simply wait for the user to connect a storage device and automatically select, or otherwise output the information to be used, read, manipulated, etc.

In its current form, it just prints to the shell, but you could assign the output to a list or variable for read/write operations and so on. It will respond to any new entries in the /dev system directory, including most USB devices, SD Cards, Webcams, and so on. You can test it by running the script in one window, and running something like sudo touch /dev/{x,y,z} in another.

I plan to use it to help people (those of us who are less technically inclined) migrate to Linux by automating the creation of bootable flash drives, but you can do what you like with it.

Open-ended feedback and suggestions are welcome. Please try to post example code pertaining to your suggestions, and don't be afraid to say something positive.

Usage:

user@macOS:~$ ./devlisten.py

/dev/disk2

/dev/rdisk2

/dev/disk2s1

/dev/rdisk2s1

Code:

#!/usr/bin/env python3



import os

import re

import time

import difflib



try:

    os.mkdir('/tmp/dev')

except FileExistsError:

    pass

except FileNotFoundError:

    print('No /tmp directory found.')

    exit()

except OSError:

    print('Read-only file system.')

    exit()



file1 = open('/tmp/dev/1', 'w')

for x in os.listdir('/dev'):

    file1.write(x + 'n')

file1.close()



try:



    diff = False

    while diff == False:

        time.sleep(0.25)



        file2 = open('/tmp/dev/2', 'w')

        for x in os.listdir('/dev'):

            file2.write(x + 'n')

        file2.close()



        text1 = open('/tmp/dev/1').readlines()

        text2 = open('/tmp/dev/2').readlines()



        for line in difflib.unified_diff(text1, text2):

            for line in re.finditer(r'(?<=^+)w.*$', line, re.MULTILINE):

                print('/dev/' + line.group(0))

                diff = True



except KeyboardInterrupt:



    print()

    exit()

edited Jan 15 at 17:34

200_success

129k15153416

asked Jan 15 at 13:48

tjt263

34639

add a comment |

Synopsis:

I plan to use it to help people (those of us who are less technically inclined) migrate to Linux by automating the creation of bootable flash drives, but you can do what you like with it.

Open-ended feedback and suggestions are welcome. Please try to post example code pertaining to your suggestions, and don't be afraid to say something positive.

Usage:

user@macOS:~$ ./devlisten.py

/dev/disk2

/dev/rdisk2

/dev/disk2s1

/dev/rdisk2s1

Code:

#!/usr/bin/env python3



import os

import re

import time

import difflib



try:

    os.mkdir('/tmp/dev')

except FileExistsError:

    pass

except FileNotFoundError:

    print('No /tmp directory found.')

    exit()

except OSError:

    print('Read-only file system.')

    exit()



file1 = open('/tmp/dev/1', 'w')

for x in os.listdir('/dev'):

    file1.write(x + 'n')

file1.close()



try:



    diff = False

    while diff == False:

        time.sleep(0.25)



        file2 = open('/tmp/dev/2', 'w')

        for x in os.listdir('/dev'):

            file2.write(x + 'n')

        file2.close()



        text1 = open('/tmp/dev/1').readlines()

        text2 = open('/tmp/dev/2').readlines()



        for line in difflib.unified_diff(text1, text2):

            for line in re.finditer(r'(?<=^+)w.*$', line, re.MULTILINE):

                print('/dev/' + line.group(0))

                diff = True



except KeyboardInterrupt:



    print()

    exit()

edited Jan 15 at 17:34

200_success

129k15153416

asked Jan 15 at 13:48

tjt263

34639

add a comment |

Synopsis:

I plan to use it to help people (those of us who are less technically inclined) migrate to Linux by automating the creation of bootable flash drives, but you can do what you like with it.

Open-ended feedback and suggestions are welcome. Please try to post example code pertaining to your suggestions, and don't be afraid to say something positive.

Usage:

user@macOS:~$ ./devlisten.py

/dev/disk2

/dev/rdisk2

/dev/disk2s1

/dev/rdisk2s1

Code:

#!/usr/bin/env python3



import os

import re

import time

import difflib



try:

    os.mkdir('/tmp/dev')

except FileExistsError:

    pass

except FileNotFoundError:

    print('No /tmp directory found.')

    exit()

except OSError:

    print('Read-only file system.')

    exit()



file1 = open('/tmp/dev/1', 'w')

for x in os.listdir('/dev'):

    file1.write(x + 'n')

file1.close()



try:



    diff = False

    while diff == False:

        time.sleep(0.25)



        file2 = open('/tmp/dev/2', 'w')

        for x in os.listdir('/dev'):

            file2.write(x + 'n')

        file2.close()



        text1 = open('/tmp/dev/1').readlines()

        text2 = open('/tmp/dev/2').readlines()



        for line in difflib.unified_diff(text1, text2):

            for line in re.finditer(r'(?<=^+)w.*$', line, re.MULTILINE):

                print('/dev/' + line.group(0))

                diff = True



except KeyboardInterrupt:



    print()

    exit()

edited Jan 15 at 17:34

200_success

129k15153416

asked Jan 15 at 13:48

tjt263

34639

Synopsis:

I plan to use it to help people (those of us who are less technically inclined) migrate to Linux by automating the creation of bootable flash drives, but you can do what you like with it.

Open-ended feedback and suggestions are welcome. Please try to post example code pertaining to your suggestions, and don't be afraid to say something positive.

Usage:

user@macOS:~$ ./devlisten.py

/dev/disk2

/dev/rdisk2

/dev/disk2s1

/dev/rdisk2s1

Code:

#!/usr/bin/env python3



import os

import re

import time

import difflib



try:

    os.mkdir('/tmp/dev')

except FileExistsError:

    pass

except FileNotFoundError:

    print('No /tmp directory found.')

    exit()

except OSError:

    print('Read-only file system.')

    exit()



file1 = open('/tmp/dev/1', 'w')

for x in os.listdir('/dev'):

    file1.write(x + 'n')

file1.close()



try:



    diff = False

    while diff == False:

        time.sleep(0.25)



        file2 = open('/tmp/dev/2', 'w')

        for x in os.listdir('/dev'):

            file2.write(x + 'n')

        file2.close()



        text1 = open('/tmp/dev/1').readlines()

        text2 = open('/tmp/dev/2').readlines()



        for line in difflib.unified_diff(text1, text2):

            for line in re.finditer(r'(?<=^+)w.*$', line, re.MULTILINE):

                print('/dev/' + line.group(0))

                diff = True



except KeyboardInterrupt:



    print()

    exit()

python beginner python-3.x linux macos

edited Jan 15 at 17:34

200_success

129k15153416

asked Jan 15 at 13:48

tjt263

34639

edited Jan 15 at 17:34

200_success

129k15153416

asked Jan 15 at 13:48

tjt263

34639

edited Jan 15 at 17:34

200_success

129k15153416

edited Jan 15 at 17:34

200_success

129k15153416

edited Jan 15 at 17:34

200_success

129k15153416

asked Jan 15 at 13:48

tjt263

34639

asked Jan 15 at 13:48

tjt263

34639

asked Jan 15 at 13:48

tjt263

34639

add a comment |

4 Answers
4

active

oldest

votes

This script might get the job done, but it is a rather crude and inefficient hack. Ideally, you should avoid polling every quarter second (or polling at all). Also, I see no reason to write any files to /tmp.

The ideal way to do it in Linux is to use udev. If you don't want to write a persistent udev rule, or you don't have root access, you can run /sbin/udevadm monitor --udev --property as a child process, and trigger your test whenever udevadm offers output. For a smarter script, you can can look for the ACTION=add line and take advantage of the information in the SUBSYSTEM=… and DEVPATH=… lines. DEVPATH tells you path to the device within /sys. But, even if you simply trigger your script only when any output appears, that would be a huge improvement over polling four times a second.

import itertools

from subprocess import Popen, PIPE

import re

import sys



KEYVALUE_RE = re.compile(r'([^=]+)=(.*)')



def events(stream):

    """

    Read udev events from the stream, yielding them as dictionaries.

    """

    while True:

        event = dict(

            KEYVALUE_RE.match(line).groups()

            for line in itertools.takewhile(KEYVALUE_RE.match, stream)

        )

        if event:

            yield event



try:

    UDEVADM = ['/sbin/udevadm', 'monitor', '--udev', '--property']

    with Popen(UDEVADM, stdout=PIPE, encoding='UTF-8') as udevadm:

        for event in events(udevadm.stdout):

            if event['ACTION'] == 'add' and event.get('DRIVER') == 'usb-storage':

                print(event)

                break

except KeyboardInterrupt:

    sys.exit(1)

On macOS, you can get similar information by running and monitoring the output of /usr/sbin/diskutil activity, if you are interested in storage devices. Look for lines starting with ***DiskAppeared.

from subprocess import Popen, PIPE

import sys



try:

    DISKUTIL = ['/usr/sbin/diskutil', 'activity']

    with Popen(DISKUTIL, stdout=PIPE, encoding='UTF-8') as diskutil:

        # Ignore events that describe the present state

        for line in diskutil.stdout:            

            if line.startswith('***DAIdle'):    

                break

        # Detect the first subsequent "Disk Appeared" event 

        for line in diskutil.stdout:

            if line.startswith('***DiskAppeared'):

                print(line)

                break

except KeyboardInterrupt:

    sys.exit(1)

If you are interested in non-storage devices as well, then you could take advantage of the File System Events API, possibly through the MacFSEvents Python package or the cross-platform fswatch program.

edited Jan 15 at 20:19

answered Jan 15 at 18:48

200_success

129k15153416

add a comment |

Prefer to use $TMPDIR if set, and /tmp only as a fallback. That's the standard practice that allows users to have separate, private temporary directories, for example, so don't subvert it! You probably ought to consider tempfile.TemporaryDirectory() as an alternative.

Error messages should go to standard error channel, not standard output.

I don't know Mac OS, but on Linux I'd expect you to wait on inotify, rather than polling the dev directory. There's a choice of Python interface to inotify, but I'm not in a position to recommend any in particular.

answered Jan 15 at 14:08

Toby Speight

24.5k740115

2

$begingroup$
macOS has FSEvents (en.wikipedia.org/wiki/FSEvents). I don't know much about it.
$endgroup$
– tjt263
Jan 15 at 18:17

add a comment |

context managers

You should really open and close files with the with statement see PEP343

if __name__ == '__main__': guard

Python idiom is to use a guard to ensure main is not run when being imported by another script

tempfile

As mentioned by @Toby already, there is module for creating Temporary files/directories

Why does it need to be in a file though?

You could create a list of filenames and poll for changes

And compare the lists instead of the files

answered Jan 15 at 14:29

Ludisposed

8,06222160

$begingroup$
It doesn't have to be stored in a file. I just thought it would be better than storing it in RAM the whole time.
$endgroup$
– tjt263
Jan 15 at 18:01

3

$begingroup$
@tjt263 Why would it?
$endgroup$
– Konrad Rudolph
Jan 16 at 0:46

add a comment |

Another point I didn't see mentioned:

try:

    os.mkdir('/tmp/dev')

except FileExistsError:

    pass

except blocks with pass are usually a sign that there is probably a better way. In this case, assuming you are using Python 3.2 or later, is to use os.makedirs with the exist_ok argument set to True:

os.makedirs('/tmp/dev', exist_ok=True)

answered Jan 15 at 19:21

DeepSpace

29519

$begingroup$
Why's that better? What's the difference?
$endgroup$
– tjt263
Jan 15 at 22:48

add a comment |

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4 Answers
4

active

oldest

votes

4 Answers
4

active

oldest

votes

import itertools

from subprocess import Popen, PIPE

import re

import sys



KEYVALUE_RE = re.compile(r'([^=]+)=(.*)')



def events(stream):

    """

    Read udev events from the stream, yielding them as dictionaries.

    """

    while True:

        event = dict(

            KEYVALUE_RE.match(line).groups()

            for line in itertools.takewhile(KEYVALUE_RE.match, stream)

        )

        if event:

            yield event



try:

    UDEVADM = ['/sbin/udevadm', 'monitor', '--udev', '--property']

    with Popen(UDEVADM, stdout=PIPE, encoding='UTF-8') as udevadm:

        for event in events(udevadm.stdout):

            if event['ACTION'] == 'add' and event.get('DRIVER') == 'usb-storage':

                print(event)

                break

except KeyboardInterrupt:

    sys.exit(1)

from subprocess import Popen, PIPE

import sys



try:

    DISKUTIL = ['/usr/sbin/diskutil', 'activity']

    with Popen(DISKUTIL, stdout=PIPE, encoding='UTF-8') as diskutil:

        # Ignore events that describe the present state

        for line in diskutil.stdout:            

            if line.startswith('***DAIdle'):    

                break

        # Detect the first subsequent "Disk Appeared" event 

        for line in diskutil.stdout:

            if line.startswith('***DiskAppeared'):

                print(line)

                break

except KeyboardInterrupt:

    sys.exit(1)

edited Jan 15 at 20:19

answered Jan 15 at 18:48

200_success

129k15153416

add a comment |

import itertools

from subprocess import Popen, PIPE

import re

import sys



KEYVALUE_RE = re.compile(r'([^=]+)=(.*)')



def events(stream):

    """

    Read udev events from the stream, yielding them as dictionaries.

    """

    while True:

        event = dict(

            KEYVALUE_RE.match(line).groups()

            for line in itertools.takewhile(KEYVALUE_RE.match, stream)

        )

        if event:

            yield event



try:

    UDEVADM = ['/sbin/udevadm', 'monitor', '--udev', '--property']

    with Popen(UDEVADM, stdout=PIPE, encoding='UTF-8') as udevadm:

        for event in events(udevadm.stdout):

            if event['ACTION'] == 'add' and event.get('DRIVER') == 'usb-storage':

                print(event)

                break

except KeyboardInterrupt:

    sys.exit(1)

from subprocess import Popen, PIPE

import sys



try:

    DISKUTIL = ['/usr/sbin/diskutil', 'activity']

    with Popen(DISKUTIL, stdout=PIPE, encoding='UTF-8') as diskutil:

        # Ignore events that describe the present state

        for line in diskutil.stdout:            

            if line.startswith('***DAIdle'):    

                break

        # Detect the first subsequent "Disk Appeared" event 

        for line in diskutil.stdout:

            if line.startswith('***DiskAppeared'):

                print(line)

                break

except KeyboardInterrupt:

    sys.exit(1)

edited Jan 15 at 20:19

answered Jan 15 at 18:48

200_success

129k15153416

add a comment |

import itertools

from subprocess import Popen, PIPE

import re

import sys



KEYVALUE_RE = re.compile(r'([^=]+)=(.*)')



def events(stream):

    """

    Read udev events from the stream, yielding them as dictionaries.

    """

    while True:

        event = dict(

            KEYVALUE_RE.match(line).groups()

            for line in itertools.takewhile(KEYVALUE_RE.match, stream)

        )

        if event:

            yield event



try:

    UDEVADM = ['/sbin/udevadm', 'monitor', '--udev', '--property']

    with Popen(UDEVADM, stdout=PIPE, encoding='UTF-8') as udevadm:

        for event in events(udevadm.stdout):

            if event['ACTION'] == 'add' and event.get('DRIVER') == 'usb-storage':

                print(event)

                break

except KeyboardInterrupt:

    sys.exit(1)

from subprocess import Popen, PIPE

import sys



try:

    DISKUTIL = ['/usr/sbin/diskutil', 'activity']

    with Popen(DISKUTIL, stdout=PIPE, encoding='UTF-8') as diskutil:

        # Ignore events that describe the present state

        for line in diskutil.stdout:            

            if line.startswith('***DAIdle'):    

                break

        # Detect the first subsequent "Disk Appeared" event 

        for line in diskutil.stdout:

            if line.startswith('***DiskAppeared'):

                print(line)

                break

except KeyboardInterrupt:

    sys.exit(1)

edited Jan 15 at 20:19

answered Jan 15 at 18:48

200_success

129k15153416

import itertools

from subprocess import Popen, PIPE

import re

import sys



KEYVALUE_RE = re.compile(r'([^=]+)=(.*)')



def events(stream):

    """

    Read udev events from the stream, yielding them as dictionaries.

    """

    while True:

        event = dict(

            KEYVALUE_RE.match(line).groups()

            for line in itertools.takewhile(KEYVALUE_RE.match, stream)

        )

        if event:

            yield event



try:

    UDEVADM = ['/sbin/udevadm', 'monitor', '--udev', '--property']

    with Popen(UDEVADM, stdout=PIPE, encoding='UTF-8') as udevadm:

        for event in events(udevadm.stdout):

            if event['ACTION'] == 'add' and event.get('DRIVER') == 'usb-storage':

                print(event)

                break

except KeyboardInterrupt:

    sys.exit(1)

from subprocess import Popen, PIPE

import sys



try:

    DISKUTIL = ['/usr/sbin/diskutil', 'activity']

    with Popen(DISKUTIL, stdout=PIPE, encoding='UTF-8') as diskutil:

        # Ignore events that describe the present state

        for line in diskutil.stdout:            

            if line.startswith('***DAIdle'):    

                break

        # Detect the first subsequent "Disk Appeared" event 

        for line in diskutil.stdout:

            if line.startswith('***DiskAppeared'):

                print(line)

                break

except KeyboardInterrupt:

    sys.exit(1)

edited Jan 15 at 20:19

answered Jan 15 at 18:48

200_success

129k15153416

edited Jan 15 at 20:19

answered Jan 15 at 18:48

200_success

129k15153416

answered Jan 15 at 18:48

200_success

129k15153416

answered Jan 15 at 18:48

200_success

129k15153416

add a comment |

Error messages should go to standard error channel, not standard output.

answered Jan 15 at 14:08

Toby Speight

24.5k740115

2

$begingroup$
macOS has FSEvents (en.wikipedia.org/wiki/FSEvents). I don't know much about it.
$endgroup$
– tjt263
Jan 15 at 18:17

add a comment |

Error messages should go to standard error channel, not standard output.

answered Jan 15 at 14:08

Toby Speight

24.5k740115

2

$begingroup$
macOS has FSEvents (en.wikipedia.org/wiki/FSEvents). I don't know much about it.
$endgroup$
– tjt263
Jan 15 at 18:17

add a comment |

Error messages should go to standard error channel, not standard output.

answered Jan 15 at 14:08

Toby Speight

24.5k740115

Error messages should go to standard error channel, not standard output.

answered Jan 15 at 14:08

Toby Speight

24.5k740115

answered Jan 15 at 14:08

Toby Speight

24.5k740115

answered Jan 15 at 14:08

Toby Speight

24.5k740115

answered Jan 15 at 14:08

Toby Speight

24.5k740115

2

$begingroup$
macOS has FSEvents (en.wikipedia.org/wiki/FSEvents). I don't know much about it.
$endgroup$
– tjt263
Jan 15 at 18:17

add a comment |

2

$begingroup$
macOS has FSEvents (en.wikipedia.org/wiki/FSEvents). I don't know much about it.
$endgroup$
– tjt263
Jan 15 at 18:17

macOS has FSEvents (en.wikipedia.org/wiki/FSEvents). I don't know much about it.

– tjt263
Jan 15 at 18:17

add a comment |

context managers

You should really open and close files with the with statement see PEP343

if __name__ == '__main__': guard

Python idiom is to use a guard to ensure main is not run when being imported by another script

tempfile

As mentioned by @Toby already, there is module for creating Temporary files/directories

Why does it need to be in a file though?

You could create a list of filenames and poll for changes

And compare the lists instead of the files

answered Jan 15 at 14:29

Ludisposed

8,06222160

$begingroup$
It doesn't have to be stored in a file. I just thought it would be better than storing it in RAM the whole time.
$endgroup$
– tjt263
Jan 15 at 18:01

3

$begingroup$
@tjt263 Why would it?
$endgroup$
– Konrad Rudolph
Jan 16 at 0:46

add a comment |

context managers

You should really open and close files with the with statement see PEP343

if __name__ == '__main__': guard

Python idiom is to use a guard to ensure main is not run when being imported by another script

tempfile

As mentioned by @Toby already, there is module for creating Temporary files/directories

Why does it need to be in a file though?

You could create a list of filenames and poll for changes

And compare the lists instead of the files

answered Jan 15 at 14:29

Ludisposed

8,06222160

$begingroup$
It doesn't have to be stored in a file. I just thought it would be better than storing it in RAM the whole time.
$endgroup$
– tjt263
Jan 15 at 18:01

3

$begingroup$
@tjt263 Why would it?
$endgroup$
– Konrad Rudolph
Jan 16 at 0:46

add a comment |

context managers

You should really open and close files with the with statement see PEP343

if __name__ == '__main__': guard

Python idiom is to use a guard to ensure main is not run when being imported by another script

tempfile

As mentioned by @Toby already, there is module for creating Temporary files/directories

Why does it need to be in a file though?

You could create a list of filenames and poll for changes

And compare the lists instead of the files

answered Jan 15 at 14:29

Ludisposed

8,06222160

context managers

You should really open and close files with the with statement see PEP343

if __name__ == '__main__': guard

Python idiom is to use a guard to ensure main is not run when being imported by another script

tempfile

As mentioned by @Toby already, there is module for creating Temporary files/directories

Why does it need to be in a file though?

You could create a list of filenames and poll for changes

And compare the lists instead of the files

answered Jan 15 at 14:29

Ludisposed

8,06222160

answered Jan 15 at 14:29

Ludisposed

8,06222160

answered Jan 15 at 14:29

Ludisposed

8,06222160

answered Jan 15 at 14:29

Ludisposed

8,06222160

$begingroup$
It doesn't have to be stored in a file. I just thought it would be better than storing it in RAM the whole time.
$endgroup$
– tjt263
Jan 15 at 18:01

3

$begingroup$
@tjt263 Why would it?
$endgroup$
– Konrad Rudolph
Jan 16 at 0:46

add a comment |

$begingroup$
It doesn't have to be stored in a file. I just thought it would be better than storing it in RAM the whole time.
$endgroup$
– tjt263
Jan 15 at 18:01

3

$begingroup$
@tjt263 Why would it?
$endgroup$
– Konrad Rudolph
Jan 16 at 0:46

It doesn't have to be stored in a file. I just thought it would be better than storing it in RAM the whole time.

– tjt263
Jan 15 at 18:01

@tjt263 Why would it?

– Konrad Rudolph
Jan 16 at 0:46

add a comment |

Another point I didn't see mentioned:

try:

    os.mkdir('/tmp/dev')

except FileExistsError:

    pass

os.makedirs('/tmp/dev', exist_ok=True)

answered Jan 15 at 19:21

DeepSpace

29519

$begingroup$
Why's that better? What's the difference?
$endgroup$
– tjt263
Jan 15 at 22:48

add a comment |

Another point I didn't see mentioned:

try:

    os.mkdir('/tmp/dev')

except FileExistsError:

    pass

os.makedirs('/tmp/dev', exist_ok=True)

answered Jan 15 at 19:21

DeepSpace

29519

$begingroup$
Why's that better? What's the difference?
$endgroup$
– tjt263
Jan 15 at 22:48

add a comment |

Another point I didn't see mentioned:

try:

    os.mkdir('/tmp/dev')

except FileExistsError:

    pass

os.makedirs('/tmp/dev', exist_ok=True)

answered Jan 15 at 19:21

DeepSpace

29519

Another point I didn't see mentioned:

try:

    os.mkdir('/tmp/dev')

except FileExistsError:

    pass

os.makedirs('/tmp/dev', exist_ok=True)

answered Jan 15 at 19:21

DeepSpace

29519

answered Jan 15 at 19:21

DeepSpace

29519

answered Jan 15 at 19:21

DeepSpace

29519

answered Jan 15 at 19:21

DeepSpace

29519

$begingroup$
Why's that better? What's the difference?
$endgroup$
– tjt263
Jan 15 at 22:48

add a comment |

$begingroup$
Why's that better? What's the difference?
$endgroup$
– tjt263
Jan 15 at 22:48

Why's that better? What's the difference?

– tjt263
Jan 15 at 22:48

add a comment |

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