2014-11-19 17:35:30 -0600, Eduardo A. Bustamante López:
> > So far, so good. But....
> >
> > imadev:~$ foo() { echo foo; }
> > imadev:~$ foo=bar
> > imadev:~$ is_defined3 foo ; echo $?
> > 1
>
> Ouch! Last try:
>
> is_defined4() {
> declare -p -- "$1" 2>/dev/null >&2
> }
>
> But I agree with you, the shell is tricky.
Bearing in mind that it only works for variables and not other
types or parameters (like $1, $#, $-) or array or association
elements.
There's also a grey areas if locale changes along the life of
the shell.
For instance, a script starting with:
#! /bin/bash -
export LC_ALL=C
could have a number of variables inherited from the environment
that are no longer usable because their name no longer are valid
identifiers.
declare -p $'\xe9'
For instance may report true because there was a $é variable in
the environment and the locale was for instance
fr_FR.iso885915@euro. But that $\xe9 variable (though defined) is
no longer accessible in the script since \xe9 is not a valid
identifier in the C locale.
For reference and comparison, in zsh:
- arrays are a different type from scalars and are not sparse
- $array expands to the non-empty elements in the array (and not
${array[0]} like in ksh/bash). You still need "${array[@]}" for
all the elements.
- $hash returns all the non-empty values in the hash (and not
${hash["0"]} like in ksh93 or bash)
- ${scalar[n]} expands to the nth character in $scalar (and not
the empty string (unless n == 0) in ksh/bash).
- $+var expands to 1 if $var is defined, 0 otherwise, works for
variables, array or hash elements and positional parameters.
(($+var)) && echo var is set
- $#array, $#hash, $#scalar expand to the number of elements in
$array and $hash and number of characters in $scalar.
(($#var)) && echo var not empty
- ${(t)var} expands to the type (and attributes) of that
variable.
- $parameters is a special hash in the zsh/parameters module
with that same information.
$ echo $parameters[parameters]
association-readonly-hide-hideval-special
--
Stephane
