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Full Discussion: Grab exactly one byte from a FIFO, at random intervals
Top Forums Shell Programming and Scripting Grab exactly one byte from a FIFO, at random intervals Post 302747893 by vomv1988 on Sunday 23rd of December 2012 03:52:53 PM
Old 12-23-2012
Quote:
Originally Posted by bipinajith
This might sound stupid, but can you replace this section:
Code:
# This is 'grab1byte':
                INBYTE=`cat ${MY_FIFO}`
                echo The input byte is:
                printf "${INBYTE}" | xxd -cols 1 | sed 's/^.*: //'

with
Code:
# This is 'grab1byte':
                echo The input byte is:
                xxd -cols 1 ${MY_FIFO} | sed 's/^.*: //'

and give it another try? Let us know the result please.
The output is the same with that change, but thanks for trying anyway. After removing the sed filter from the original script I posted, the output looks something like:

Code:
y: print next byte
n: don't print next byte
q: quit
y
The input byte is:
0000000: 48  H
0000001: 65  e
y: print next byte
n: don't print next byte
q: quit
y
The input byte is:
0000000: 6c  l
0000001: 6c  l
0000002: 6f  o
0000003: 2c  ,
0000004: 20   
0000005: 77  w
y: print next byte
n: don't print next byte
q: quit

So this means that the FIFO buffer contains several bytes instead of just one... Which is weird, because, I thought 'printf "${CHAR}" > ${MY_FIFO}"' was supposed to pause the loop execution, UNTIL FIFO was emptied by something like 'cat ${MY_FIFO}'. After cat-ing FIFO, I thought the loop would freeze again at 'printf "${CHAR}" > ${MY_FIFO}"', until another instance of 'cat ${MY_FIFO}', but, apparently it doesn't. Apparently, it just feeds FIFO a random amount of bytes... WHY???

---------- Post updated at 04:52 PM ---------- Previous update was at 04:44 PM ----------

I'm thinking, maybe, cat opens up the FIFO for a longer time than it takes the loop to iterate, so the loop iterates several times, spitting several bytes into FIFO, until cat stops reading from FIFO (that is, until FIFO's output is closed)... Does this make any sense to you? And, if that is the case: How would I prevent that from happening?
 

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LEARN ABOUT HPUX

orientation

orientation(5)							File Formats Manual						    orientation(5)

NAME

       orientation - the orientation of a stream

DESCRIPTION

       The  orientation  of a stream is a property of a object that is handled as a input/output stream.  It is useful when the input/output model
       assumes that characters are handled as wide-characters within an application and stored as multi-byte characters in files, and that all the
       wide-character input/output functions begin executing with the stream positioned at the boundary between two multi-byte characters.

       After  a  stream is associated with a file, but before any operations are performed on the stream, the stream is without orientation.  If a
       wide-character input or output function is applied to a stream without orientation, the stream becomes wide-oriented implicitly.  Likewise,
       if  a  byte  input  or  output operation is applied to a stream without orientation, the stream becomes byte-oriented implicitly.  Only the
       function can alter the orientation of a stream explicitly when the stream is without orientation.

       Just after a stream is associated with a pipe by the function, the stream is byte-oriented.

       After the stream becomes byte-oriented or wide-oriented, the orientation of a stream will be fixed and can not be changed until the  stream
       is closed.

       The following functions are wide-character input/output functions.

       The following functions are byte input/output functions.

EXAMPLES

       To read characters from a stream when the orientation of the stream is unknown :

WARNINGS

       If  byte  input/output  functions are applied to a wide-oriented stream or wide-character input/output functions are applied to a byte-ori-
       ented stream, the behavior is undefined.

AUTHOR

       The functionality of the orientation of a stream was developed by HP and Mitsubishi Electric Corporation.

SEE ALSO

       fgetws(3C), fopen(3S), fread(3S), fwide(3C), fwprintf(3C), fwscanf(3C), getc(3S), gets(3S),  getwc(3C),	popen(3S),  printf(3S),  putc(3S),
       puts(3S), putwc(3C), putws(3C), scanf(3S), ungetc(3S), ungetwc(3C).

																    orientation(5)
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