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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 302284744 by otheus on Friday 6th of February 2009 08:50:29 AM
Old 02-06-2009
Actually, it's not the ""[[ ]]" construct nor the "[ ]" construct, but the && construct that does the trick. There is no standard way, however, of doing negation in the UNIX shell using the && || constructs. One can, however, do something like this:
Code:
not() { 
  "$@"
  if [ $? = 0 ]; then return 1; else return 0; fi
}

# not true || echo false
false
# not false && echo true
true

You can also group things together between { }:
Code:
# not true || { echo false; date; echo really false; false; } || echo Total failure.
false
really false
Total failure.
# not true || { echo false; echo really false; true; } && echo not a total failure.
false
really false
not a total failure.

Does that help?

You should be able now to do:
Code:
command_A && { command_A_worked; command_A_worked_report; true; } || { command_A_failed; command_A_failed_report; false; }

 

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LEARN ABOUT OSF1

false

true(1) 						      General Commands Manual							   true(1)

NAME

       true, false - Returns a standard exit value

SYNOPSIS

       true

       false

STANDARDS

       Interfaces documented on this reference page conform to industry standards as follows:

       true:  XCU5.0

       false:  XCU5.0

       Refer to the standards(5) reference page for more information about industry standards and associated tags.

DESCRIPTION

       The true command returns a 0 (zero) exit value. The false command returns a nonzero exit value. These commands are usually used in input to
       shell commands.

NOTES

       The special built-in utility : (colon) is sometimes more efficient than the true command.

EXIT STATUS

       [Tru64 UNIX]  The nonzero value returned by the false command may vary from system to system.

EXAMPLES

       To construct a loop in a shell procedure, enter: while true do	   date      sleep 60 done

       This procedure displays the date and time once a minute.  To stop it, press the Interrupt key sequence.

SEE ALSO

       Commands:  csh(1), ksh(1), Bourne Shell sh(1b), POSIX shell sh(1p)

       Standards:  standards(5)

																	   true(1)
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