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Top Forums UNIX for Advanced & Expert Users meaning of the construction: ${1+"$@"} ? Post 302489072 by alex_5161 on Wednesday 19th of January 2011 11:58:05 AM
Old 01-19-2011
meaning of the construction: ${1+"$@"} ?

Whoud anybody explain the reason to have such construction in code: ${1+"$@"}

It is used in the function that replasing functionality of the 'cd' command by processing the 'cd' itself and after that processing some other stuff:
Code:
chdir() {
   'cd' ${1+"$@"}
   ...  #other stuff
}

I understand it intends to aply function parameters to the 'cd' command.
I do not understand NEEDS for that extra-smartness.
Why not just '$*' or '$@'?
Also I am not clear about that syntaxis: I see it use the first parameter: $1, ${1}; but the '+"..."' - what is it?
If that is kind of concatenation, the "$@" - means all parameters (as set of words, I guess); so it would duplicate the first parameter: it is already mentioned before '+' and also included in $@; but, not, it is not repeating.

If someone could explain what is used here and what is the benefit from that sysntax, I will appreciate!
 

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IRSEND(1)								FSF								 IRSEND(1)

NAME
irsend - basic LIRC program to send infra-red commands SYNOPSIS
irsend [options] DIRECTIVE REMOTE CODE [CODE...] DESCRIPTION
Asks the lircd daemon to send one or more CIR (Consumer Infra-Red) commands. This is intended for remote control of electronic devices such as TV boxes, HiFi sets, etc. DIRECTIVE can be: SEND_ONCE - send CODE [CODE ...] once SEND_START - start repeating CODE SEND_STOP - stop repeating CODE LIST - list configured remote items SET_TRANSMITTERS - set transmitters NUM [NUM ...] SIMULATE - simulate IR event REMOTE is the name of a remote, as described in the lircd configuration file. CODE is the name of a remote control key of REMOTE, as it appears in the lircd configuration file. NUM is the transmitter number of the hardware device. For the LIST DIRECTIVE, REMOTE and/or CODE can be empty: LIST "" "" - list all configured remote names LIST REMOTE "" - list all codes of REMOTE LIST REMOTE CODE - list only CODE of REMOTE The SIMULATE command only works if it has been explicitly enabled in lircd. -h --help display usage summary -v --version display version -d --device use given lircd socket [/var/run/lirc/lircd] -a --address=host[:port] connect to lircd at this address -# --count=n send command n times EXAMPLES
irsend LIST DenonTuner "" irsend SEND_ONCE DenonTuner PROG-SCAN irsend SEND_ONCE OnkyoAmpli VOL-UP VOL-UP VOL-UP VOL-UP irsend SEND_START OnkyoAmpli VOL-DOWN ; sleep 3 irsend SEND_STOP OnkyoAmpli VOL-DOWN irsend SET_TRANSMITTERS 1 irsend SET_TRANSMITTERS 1 3 4 irsend SIMULATE "0000000000000476 00 OK TECHNISAT_ST3004S" FILES
/etc/lirc/lircd.conf Default lircd configuration file. It should contain all the remotes, their infra-red codes and the corresponding timing and wave- form details. DIAGNOSTICS
If lircd is not running (or /var/run/lirc/lircd lacks write permissions) irsend aborts with the following diagnostics: "irsend: could not connect to socket" "irsend: Connection refused" (or "Permission denied"). SEE ALSO
The documentation for lirc is maintained as html pages. They are located under html/ in the documentation directory. lircd(8), mode2(1), smode2(1), xmode2(1), irrecord(1), irw(1), http://www.lirc.org. irsend 0.8.7pre1 May 2010 IRSEND(1)
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