Hi Dan, On Thu, 16 Mar 2017 14:30:06 -0500, Dan Douglas wrote: > On 03/14/2017 05:08 AM, Jean Delvare wrote: > > So internally bash does make a difference between a variable being > > null and a variable being unset. A bash variable can actually have 4 > > distinct states: non-existent, existent but unset, set but null, and > > non-null. "typeset", "local" and "unset" all put the variable into > > state "existent but unset" (unlike mksh.) > > It depends on context and the type of variable involved. Arrays complicate > things and namerefs _really_ complicate things. In bash, declaring a > simple local scalar, assigning it a value, then unsettling it within > the same scope brings the variable back to the same "hidden local" > state it is in when declared local but not given a value. However, > unsetting the local from a child scope does fully destroy the local, > uncovering the variables in parent scopes.
For the least educated of us, of which I am, can you explain what you mean by "child scope"? > Thus bash's is actually the most flexible of the dynamic scope systems > in some ways. If you want bash to behave like mksh just define a wrapper > function for unset (I usually name it `unset2'). Contrast with zsh, What I needed was the opposite, and Thorsten helped me achieve that. > which has no way to unset a local (last I checked, which was years > ago). In addition, bash has `declare -g' for directly acting on the > global scope. It has a few good uses e.g. for setting special variables > like PATH or LC_*. Thanks, -- Jean Delvare SUSE L3 Support
