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Top Forums UNIX for Advanced & Expert Users Redirection? (I do find some of the strangest things.) Post 302989217 by RudiC on Tuesday 10th of January 2017 05:06:14 AM
Old 01-10-2017
Hmmm, quite some questions in one post. And, I can't comment for all thoses OSes nor all shells, nor on shellcheck. For bash on linux and FreeBSD,
- You can have any number of redirections in a command line any place; they're evaluated left to right, and the last one will be effective. Check what >/tmp/1 cat file1 > /tmp/2 > /tmp/3 does.
- In your line > /dev/null 2>&1 cat /tmp/noise.raw > /dev/dsp it might be interesting to check where the error msgs go. What be your first guess?
- You don't need a command nor a NOP; >/tmp/1 will just open the file, empty it, and close it. This can be (and is) used to effectively create an empty file.
- That shellcheck comment seems to be a warning, not an error. shells allow for that construct.
- Your conclusion about non-existence of /dev/dsp from the permission error might be incorrect.
 

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rmvb(9F)						   Kernel Functions for Drivers 						  rmvb(9F)

NAME
rmvb - remove a message block from a message SYNOPSIS
#include <sys/stream.h> mblk_t *rmvb(mblk_t *mp, mblk_t *bp); INTERFACE LEVEL
Architecture independent level 1 (DDI/DKI). PARAMETERS
mp Message from which a block is to be removed. mblk_t is an instance of the msgb(9S) structure. bp Message block to be removed. DESCRIPTION
The rmvb() function removes a message block (bp) from a message (mp), and returns a pointer to the altered message. The message block is not freed, merely removed from the message. It is the module or driver's responsibility to free the message block. RETURN VALUES
If successful, a pointer to the message (minus the removed block) is returned. The pointer is NULL if bp was the only block of the message before rmvb() was called. If the designated message block (bp) does not exist, -1 is returned. CONTEXT
The rmvb() function can be called from user, interrupt, or kernel context. EXAMPLES
This routine removes all zero-length M_DATA message blocks from the given message. For each message block in the message, save the next message block (line 10). If the current message block is of type M_DATA and has no data in its buffer (line 11), then remove it from the message (line 12) and free it (line 13). In either case, continue with the next message block in the message (line 16). 1 void 2 xxclean(mp) 3 mblk_t *mp; 4 { 5 mblk_t *tmp; 6 mblk_t *nmp; 7 8 tmp = mp; 9 while (tmp) { 10 nmp = tmp->b_cont; 11 if ((tmp->b_datap->db_type == M_DATA) && (tmp->b_rptr == tmp->b_wptr)) { 12 (void) rmvb(mp, tmp); 13 freeb(tmp); 14 } 15 tmp = nmp; 16 } 17 } SEE ALSO
freeb(9F), msgb(9S) Writing Device Drivers STREAMS Programming Guide SunOS 5.11 16 Jan 2006 rmvb(9F)
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