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Full Discussion: Question on using "[[ ]]" in lieu of IF Construct
Top Forums Shell Programming and Scripting Question on using "[[ ]]" in lieu of IF Construct Post 302285085 by cfajohnson on Saturday 7th of February 2009 03:07:24 AM
Old 02-07-2009
Quote:
Originally Posted by sunpraveen
Unix gurus,

I have a piece of code as below.

Code:
[[ -n ${ORACLE_SID} ]] && INST="${ORACLE_SID}" || INST="${TWO_TASK}"


The [[ ... ]] syntax is non-standard. In almost all cases, you can use the standard [ ... ].
Quote:

I know that the above code can be used in lieu of an IF construct. I also know that the above code can be extended for the "true" condition to include more than one command (as below):

Code:
[[ -n ${ORACLE_SID} ]] && INST="${ORACLE_SID}" && echo "INST=${INST}" || INST="${TWO_TASK}"

But I am unable to extend the "false" condition to include more than one command.

Code:
[ -n "$ORACLE_SID" ] && {
 INST=$ORACLE_SID"
 echo "INST=$INST"
} || {
 INST=$TWO_TASK
 echo "INST=$INST"
}

However, you should note that, in the general case, that is not the same as:

Code:
if [ -n "$ORACLE_SID" ]
then
 : do whatever
else
 : do something else
fi

A simplified example:

Code:
[ -n "$qwerty" ] && false || echo "FAIL!"

"FAIL!" will always be printed. The command after || is executed if either of the preceding commands fails.
 

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LEARN ABOUT DEBIAN

acpi_wmi

ACPI_WMI(4)						 BSD/i386 Kernel Interfaces Manual					       ACPI_WMI(4)

NAME

     acpi_wmi -- ACPI to WMI mapping driver

SYNOPSIS

     To compile this driver into the kernel, place the following line in your kernel configuration file:

	   device acpi_wmi

     Alternatively, to load the driver as a module at boot time, place the following line in loader.conf(5):

	   acpi_wmi_load="YES"

DESCRIPTION

     The acpi_wmi driver provides an interface for vendor specific WMI implementations (e.g. HP and Acer laptops).  It creates /dev/wmistat, which
     can be read to get information about GUIDs found in the system.

FILES

     /dev/wmistat  WMI status device.

EXAMPLES

     # cat /dev/wmistat GUID				      INST EXPE METH STR EVENT OID {5FB7F034-2C63-45E9-BE91-3D44E2C707E4}   1 NO   WMAA NO
     NO    AA {95F24279-4D7B-4334-9387-ACCDC67EF61C}   1 NO   NO   NO  0x80+ - {2B814318-4BE8-4707-9D84-A190A859B5D0}	1 NO   NO   NO	0xA0  -
     {05901221-D566-11D1-B2F0-00A0C9062910}   1 NO   NO   NO  NO    AB {1F4C91EB-DC5C-460B-951D-C7CB9B4B8D5E}	1 NO   WMBA NO	NO    BA
     {2D114B49-2DFB-4130-B8FE-4A3C09E75133}  57 NO   NO   NO  NO    BC {988D08E3-68F4-4C35-AF3E-6A1B8106F83C}  20 NO   NO   NO	NO    BD
     {14EA9746-CE1F-4098-A0E0-7045CB4DA745}   1 NO   NO   NO  NO    BE {322F2028-0F84-4901-988E-015176049E2D}	2 NO   NO   NO	NO    BF
     {8232DE3D-663D-4327-A8F4-E293ADB9BF05}   0 NO   NO   NO  NO    BG {8F1F6436-9F42-42C8-BADC-0E9424F20C9A}	0 NO   NO   NO	NO    BH
     {8F1F6435-9F42-42C8-BADC-0E9424F20C9A}   0 NO   NO   NO  NO    BI

SEE ALSO

     acpi(4),

HISTORY

     The acpi_wmi device driver first appeared in FreeBSD CURRENT.

AUTHORS

     The acpi_wmi driver was written by Michael Gmelin <freebsd@grem.de>

     Work has been inspired by the Linux acpi-wmi driver written by Carlos Corbacho

     See http://www.microsoft.com/whdc/system/pnppwr/wmi/wmi-acpi.mspx for the specification of ACPI-WMI.

     This manual page was written by Michael Gmelin <freebsd@grem.de>

BSD
								   June 30, 2009							       BSD
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