Re: tilde syntax

When you include the value of a variable (parameter) in a command line, the replacement usually happens too late for the resulting value to participate in other sorts of expansion.

For example, if you do `echo *`, you'll get a list of the files in the directory. But if you put the `*` into a variable and echo it:

$ asterisk='*'

$ echo $asterisk

Likewise, if you have a variable with a space in the value, it's not normally subject to word splitting - if you pass it to a command, that command will get a single argument containing a space, not multiple arguments:

$ words='one two'

$ printf '%s\n' $words

one two

(It's worth mentioning that in both of the above cases the behavior of zsh is different from the behavior of bash or ksh, in which the parameter value _is_ subject to further expansion.)

You can selectively enable further processing with the `~` and `=` modifiers. The `~` means that the result of the variable substitution will be subject to wildcard expansion:

$ echo $~asterisk

Applications Desktop Documents Downloads Library bin etc git lib src tmp

While the `=` means it will be subject to word-splitting:

$ printf '%s\n' $=words

one

two

On Thu, Jan 4, 2024 at 9:04 PM Ray Andrews <rayandrews@xxxxxxxxxxx> wrote:

On 2024-01-04 17:41, Lawrence Velázquez wrote:
Another important part occurs earlier in "Parameter Expansion" and
can admittedly be hard to find:
Yes. Seems almost inevitable that with such terse syntax normal search

culture is going to be frustrating. One must master the shell's jargon.

I wonder if a syntax index could be contemplated, it would look rather strange:

$(

$((

$~

${~

if[

if[[

... every last construction.
This is why you can use $~foo instead of ${~foo} sometimes.
I've noticed that but I don't even try to understand it. I am in awe of the

geniuses who wrote the parser. The list of ifs, ands, buts and maybes is

not for a mere mortal to understand. That's what accretion gets you -- couldn't

be otherwise.
That just refers to the result of the parameter expansion being
subsequently used as something other than a literal value, if the
context calls for it.
God knows. It's a steep hill to climb if you're not familiar with it. Anyway I'm

at least alert to the issue.

Tx.