What does ${x} mean? Post: 303031695

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Top Forums Shell Programming and Scripting What does ${x} mean? Post 303031695 by rbatte1 on Monday 4th of March 2019 12:17:04 PM

03-04-2019

Moderator

The { and } are very useful for clarity. It is also very useful for these cases too:-

You want to refer to command line parameter ten or over. Some OSes would interpret $10 as actually the first parameter suffixed with a zero. You would need to refer to ${10} instead.
You might want to refer to a variable and put in a suffix of your own, then $var_suffix will not work, but ${var}_suffix will. The _suffix will be treated as though it is part of the variable name with the first format, but is just literal text appended after the value of the variable in the latter.

The second case might be a bit obscure, so perhaps a demonstration on the command line is better:-

Code:

$ a=Hello
$ a_b=world
$ echo $a
Hello
$ echo $a_b
world
$ echo ${a}_b
Hello_b

I hope that this helps and that I haven't confused things.
Robin

Last edited by rbatte1; 03-05-2019 at 06:41 AM.. Reason: Corrected my example. Oh how wrong I was trying to illustrate the issue but getting it backwards!

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LEARN ABOUT DEBIAN

irsend

IRSEND(1)							   User Commands							 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 0.9.0-pre1						   October 2010 							 IRSEND(1)