How can I replace “cat” and “echo” read/write command with python/c program?
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I have trouble replacing device in/output commands like:
echo 100 > /dev/rtmotor_raw_l0 # output 100hz frequency
cat /dev/rtswitch0 # read switch state
output problem(python)
I tried replacing that command with python.
file = open('/dev/rtmotor_raw_l0','w')
file.write('100n') # I want output in this timing
file.close() # output reflected after closing file
The problem is that the output appears after closing the file.
Does this mean I have to open and close this device each time I want to change its value? Also, changing 'w' to 'a' did not work.
input problem(python)
Almost the same problem happens in input observation.
file = open('/dev/rtswitch','r')
file.read() # works
file.read() # after first read it does't work anymore
file.close() # need to reopen the file to get newer value
I could only read 1 input in each opening files.
So, currently I have to reopen the devices each time I want to write/read new values.
Are there any way to avoid this problem?
Thank you.
command-line python echo
asked Feb 1 at 12:18
Y. RiY. Ri
84
migrated from superuser.com Feb 1 at 14:31
This question came from our site for computer enthusiasts and power users.
add a comment |
I have trouble replacing device in/output commands like:
echo 100 > /dev/rtmotor_raw_l0 # output 100hz frequency
cat /dev/rtswitch0 # read switch state
output problem(python)
I tried replacing that command with python.
file = open('/dev/rtmotor_raw_l0','w')
file.write('100n') # I want output in this timing
file.close() # output reflected after closing file
The problem is that the output appears after closing the file.
Does this mean I have to open and close this device each time I want to change its value? Also, changing 'w' to 'a' did not work.
input problem(python)
Almost the same problem happens in input observation.
file = open('/dev/rtswitch','r')
file.read() # works
file.read() # after first read it does't work anymore
file.close() # need to reopen the file to get newer value
I could only read 1 input in each opening files.
So, currently I have to reopen the devices each time I want to write/read new values.
Are there any way to avoid this problem?
Thank you.
command-line python echo
asked Feb 1 at 12:18
Y. RiY. Ri
84
migrated from superuser.com Feb 1 at 14:31
This question came from our site for computer enthusiasts and power users.
1
After the first read, the file pointer is at the end of the file; assuming'/dev/rtswitchis seekable, you need to rewind the file pointer to the beginning of the file before you can read the contents again: putfile.seek(0)between the two reads.
– chepner
Feb 1 at 14:53
add a comment |
I have trouble replacing device in/output commands like:
echo 100 > /dev/rtmotor_raw_l0 # output 100hz frequency
cat /dev/rtswitch0 # read switch state
output problem(python)
I tried replacing that command with python.
file = open('/dev/rtmotor_raw_l0','w')
file.write('100n') # I want output in this timing
file.close() # output reflected after closing file
The problem is that the output appears after closing the file.
Does this mean I have to open and close this device each time I want to change its value? Also, changing 'w' to 'a' did not work.
input problem(python)
Almost the same problem happens in input observation.
file = open('/dev/rtswitch','r')
file.read() # works
file.read() # after first read it does't work anymore
file.close() # need to reopen the file to get newer value
I could only read 1 input in each opening files.
So, currently I have to reopen the devices each time I want to write/read new values.
Are there any way to avoid this problem?
Thank you.
command-line python echo
asked Feb 1 at 12:18
Y. RiY. Ri
84
I have trouble replacing device in/output commands like:
echo 100 > /dev/rtmotor_raw_l0 # output 100hz frequency
cat /dev/rtswitch0 # read switch state
output problem(python)
I tried replacing that command with python.
file = open('/dev/rtmotor_raw_l0','w')
file.write('100n') # I want output in this timing
file.close() # output reflected after closing file
The problem is that the output appears after closing the file.
Does this mean I have to open and close this device each time I want to change its value? Also, changing 'w' to 'a' did not work.
input problem(python)
Almost the same problem happens in input observation.
file = open('/dev/rtswitch','r')
file.read() # works
file.read() # after first read it does't work anymore
file.close() # need to reopen the file to get newer value
I could only read 1 input in each opening files.
So, currently I have to reopen the devices each time I want to write/read new values.
Are there any way to avoid this problem?
Thank you.
command-line python echo
command-line python echo
asked Feb 1 at 12:18
Y. RiY. Ri
84
asked Feb 1 at 12:18
Y. RiY. Ri
84
asked Feb 1 at 12:18
Y. RiY. Ri
84
asked Feb 1 at 12:18
Y. RiY. Ri
84
asked Feb 1 at 12:18
Y. RiY. Ri
84
84
migrated from superuser.com Feb 1 at 14:31
This question came from our site for computer enthusiasts and power users.
migrated from superuser.com Feb 1 at 14:31
This question came from our site for computer enthusiasts and power users.
1
After the first read, the file pointer is at the end of the file; assuming'/dev/rtswitchis seekable, you need to rewind the file pointer to the beginning of the file before you can read the contents again: putfile.seek(0)between the two reads.
– chepner
Feb 1 at 14:53
add a comment |
1
After the first read, the file pointer is at the end of the file; assuming'/dev/rtswitchis seekable, you need to rewind the file pointer to the beginning of the file before you can read the contents again: putfile.seek(0)between the two reads.
– chepner
Feb 1 at 14:53
1
1
After the first read, the file pointer is at the end of the file; assuming
'/dev/rtswitch is seekable, you need to rewind the file pointer to the beginning of the file before you can read the contents again: put file.seek(0) between the two reads.– chepner
Feb 1 at 14:53
After the first read, the file pointer is at the end of the file; assuming
'/dev/rtswitch is seekable, you need to rewind the file pointer to the beginning of the file before you can read the contents again: put file.seek(0) between the two reads.– chepner
Feb 1 at 14:53
add a comment |
1 Answer
1
active
oldest
votes
Try call file.flush() after write() call. It will flush buffer to file and you can read data.
answered Feb 1 at 12:44
MatejMatej
3901311
add a comment |
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1 Answer
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1 Answer
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Try call file.flush() after write() call. It will flush buffer to file and you can read data.
answered Feb 1 at 12:44
MatejMatej
3901311
add a comment |
Try call file.flush() after write() call. It will flush buffer to file and you can read data.
answered Feb 1 at 12:44
MatejMatej
3901311
add a comment |
Try call file.flush() after write() call. It will flush buffer to file and you can read data.
answered Feb 1 at 12:44
MatejMatej
3901311
Try call file.flush() after write() call. It will flush buffer to file and you can read data.
answered Feb 1 at 12:44
MatejMatej
3901311
answered Feb 1 at 12:44
MatejMatej
3901311
answered Feb 1 at 12:44
MatejMatej
3901311
answered Feb 1 at 12:44
MatejMatej
3901311
3901311
add a comment |
add a comment |
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After the first read, the file pointer is at the end of the file; assuming
'/dev/rtswitchis seekable, you need to rewind the file pointer to the beginning of the file before you can read the contents again: putfile.seek(0)between the two reads.– chepner
Feb 1 at 14:53