How can I replace “cat” and “echo” read/write command with python/c program?
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
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
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/rtswitch
is 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
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
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/rtswitch
is 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/rtswitch
is 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.
add a comment |
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1 Answer
1
active
oldest
votes
1 Answer
1
active
oldest
votes
active
oldest
votes
active
oldest
votes
Try call file.flush()
after write()
call. It will flush buffer to file and you can read data.
add a comment |
Try call file.flush()
after write()
call. It will flush buffer to file and you can read data.
add a comment |
Try call file.flush()
after write()
call. It will flush buffer to file and you can read data.
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
3781310
3781310
add a comment |
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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: putfile.seek(0)
between the two reads.– chepner
Feb 1 at 14:53