[Tutor] regular expression

[Kent Johnson]

arbaro arbaro wrote:
> Hello,
>
> I'm trying to mount an usb device from python under linux.
> To do so, I read the kernel log /proc/kmsg and watch for something like:
>   "<6> /dev/scsi/host3/bus0/target0/lun0/:<7>usb-storage: device scan 
> complete"
>
> When I compile a regular expression like:
>   "r = re.compile('<\d+>\s/dev/scsi/host\d+/bus\d+/target\d+/lun\d+')"
You should use raw strings for regular expressions that contain \ 
characters.
> It is found. But I don't want the <\d+>\s or '<6> ' in front of the 
> path, so I tried:
>    "r = re.compile('/dev/scsi/host\d+/bus\d+/target\d+/lun\d+')"
> But this way the usb device path it is not found.
You are using re.match(), which just looks for a match at the start of 
the string. Try using re.search() instead.
http://docs.python.org/lib/matching-searching.html

Kent
>
> So what i'm trying to do is:
> - find the usb device path from the kernel log with the regular 
> expression.
> - Determine the start and end positions of the match (and add /disc or 
> /part1 to the match).
> - And use that to mount the usb stick on /mnt/usb -> mount -t auto 
> match /mnt/usb
>
> If anyone can see what i'm doing wrong, please tell me, because I 
> don't understand it anymore.
> Thanks.
>
> Below is the code:
>
> # \d+ = 1 or more digits
> # \s  = an empty space
>
> import re
>
> def findusbdevice():
>     ''' Returns path of usb device '''
>     # I did a 'cat /proc/kmsg /log/kmsg' to be able to read the kernel 
> message.
>     # Somehow I can't read /proc/kmsg directly.
>     kmsg = open('/log/kmsg', 'r')
>     r = re.compile('/dev/scsi/host\d+/bus\d+/target\d+/lun\d+')
>     #r = re.compile('<\d+>\s/dev/scsi/host\d+/bus\d+/target\d+/lun\d+')
>     for line in kmsg:
>         if 'usb-storage' in line and r.match(line):
>             print 'Success', line
> ------------------------------------------------------------------------
>
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