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Top Forums Shell Programming and Scripting What does the "!" in "${!VARIABLE:-\n}" mean? Post 303023693 by da1 on Friday 21st of September 2018 04:16:19 AM
Old 09-21-2018
What does the "!" in "${!VARIABLE:-\n}" mean?

so I'm going over this script someone else wrote and I haven't seen the aforementioned construct before.


The code says:
Code:
declare VAR1="${!VARIABLE:-\n}"


I know what the ":-\n" does but I don't understand why would one negate ("!") the variable in the first place. Am I reading this right that even if VARIABLE is set, always fall back to the default (:-\n)?



PS: "VARIABLE" is defined at the beginning of the script as "VARIABLE=test"
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CTL(5)                                              CTL file format of ASIM/LIP6/CAO-VLSI lab.                                              CTL(5)

NAME
ctl - Control Temporal Logic file format. ORIGIN
This software belongs to the ALLIANCE CAD SYSTEM developed by the ASIM team at LIP6 laboratory of Universite Pierre et Marie CURIE, in Paris, France. Web : http://asim.lip6.fr/recherche/alliance/ E-mail : alliance-users@asim.lip6.fr DESCRIPTION
This document describes the CTL file format used by moka(1) for model checking of finite states machine description. This CTL file format subset is defined to enable classical CTL formulae description. A CTL file is made of two parts: a declaration part and a formulae statement part. The declaration part described types, constants, macros and all variables used in CTL formulae. It also describes assumption conditions and initial conditions that have to be applied by moka(1) during the model checking. The formulae statement part described all the CTL formulae that have to be verified. All boolean and relational VHDL operators are supported (see vbe(5)) and also the 8 CTL operators AF, AG, AX, AU, EF, EG, EX and EU. The CTL file format support also the imply boolean operator '->' and the equivalence operator '<=>'. EXAMPLE
-- user type definition TYPE A_ETAT_TYPE IS (A_E0, A_E1); TYPE B_ETAT_TYPE IS (B_E0, B_E1); -- variables definition VARIABLE A_NS, A_CS : A_ETAT_TYPE; VARIABLE B_NS, B_CS : B_ETAT_TYPE; VARIABLE ck : BIT; VARIABLE data_in : BIT; VARIABLE data_out : BIT; VARIABLE reset : BIT; VARIABLE ack : BIT; VARIABLE req : BIT; -- example of a macros definition DEFINE def1 : BOOLEAN := ack='1'; -- the assigned value can be a constant DEFINE c1 : BIT := '1'; -- the assumption condition ASSUME ass1 := (reset='0'); -- the initial reset condition -- be careful, the assumption condition is not applied -- to the initial conditions. RESET_COND init1 := (reset='1'); -- It is also possible to describe the first state -- with the INITIAL keywork, as follows: -- -- INITIAL init1 := ((A_CS=A_E0) AND (B_CS=B_E0)); -- -- formulae description statement part begin prop1 : EX( ack='1' ); prop2 : AG( req -> AF( ack ) ); prop4 : AU( req='1', ack='1'); end; SEE ALSO
moka(1) BUG REPORT
This tool is under development at the ASIM department of the LIP6 laboratory. We need your feedback to improve documentation and tools. ASIM
/LIP6 August 5, 2002 CTL(5)
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