On 5/4/15 9:03 PM, James Caccese wrote:
> I posted the following question to stackoverflow
> (
http://stackoverflow.com/questions/30042157/why-cant-i-use-declare-r-inside-a-function-fo-mark-a-variable-readonly-while)
> and was advised the behavior I was witnessing was a bug in bash.
It's not a bug; it's an application of bash's scoping rules and the rules
about when a varible is not set.
>
> With |GNU bash, version 4.3.11(1)-release (x86_64-pc-linux-gnu)|,
>
> |#! /bin/bash
> set -u
>
> exec {FD1}>tmp1.txt
> declare -r FD1
> echo "fd1: $FD1" # why does this work,
You create a global variable and modify its attributes.
>
> function f1() {
> exec {FD2}>tmp2.txt
> readonly FD2
> echo "fd2: $FD2" # this work,
You create a global variable and modify its attributes.
> }
>
> f1
>
> function f2() {
> exec {FD3}>tmp3.txt
> echo "fd3: $FD3" # and even this work,
You create a global variable.
> declare -r FD3
You create a `placeholder' local variable that has no value, shadowing the
global variable. When you use `declare' or its synonym `typeset' inside a
shell function, you create local variables.
The variable has no value, since you haven't assigned it one, and so is
technically unset.
> echo "fd3: $FD3" # when this complains: "FD3: unbound variable"?
Scoping: the variable with that name in the closest scope is the (unset)
local copy of FD3.
--
``The lyf so short, the craft so long to lerne.'' - Chaucer
``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, ITS, CWRU
chet@case.edu http://cnswww.cns.cwru.edu/~chet/