> Since those are not numeric, bash treats them as expressions to be
> evaluated. You don't have to use the $ to obtain variable evaluation
> when using [[ or [. You get:
c=1;a="c";b=2;[[ a -lt b ]]; echo $?
0
c=3;a="c";b=2;[[ a -lt b ]]; echo $?
1
I see. I was aware of explicit indirection as described in the man page section
"Parameter Expansion", with the syntax ${!name}. I wasn't aware of the above
implicit indirection with [[ expression ]].
But, for [ expression ], I have to use explicit indirection with ${!a} otherwise
I get an error, "bash: [: a: integer expression expected".
This brings up some interesting situations with indirection and declare:
# f is assigned the value of z through implicit indirection
unset z f;declare -i z=5;declare -i f="z";declare -p z f
declare -i z="5"
declare -i f="5"
# f is assigned the default value of 0 when z is not defined
# for implicit indirection
unset z f;declare -i f="z";declare -p z f
bash: declare: z: not found
declare -i f="0"
# f is assigned the default value of 0 when empty variable name
# is used for implicit indirection
unset z f;declare -i f="";declare -p z f
bash: declare: z: not found
declare -i f="0"
#
unset z f;declare -i f;echo $?;echo \"$f\";declare -p z f
0
""
bash: declare: z: not found
bash: declare: f: not found
It would be helpful if indirection was explained in the documentation for
[[ expression ]], [ expression ], and declare.
Thank you.
Peg
