What are the types of ~, ~-, ~+, *?

Question

If I am correct, pwd is a command, PWD is a variable('s name), and - in cd - is an operand.

What are the types of ~, ~-, ~+, * when they mean $HOME, the previous visited dir, the current dir, and the files under current dir? (from programming languages' perspective)

Are they variables' names? If yes, why does echo $~ not work?

Why does * work in:

for i in *; do ls "$i"; done

Please search the U&L site before asking such basic/fundamental Q's. Much of what you ask is covered throughout. For ex. tildes are discussed here: Does ~ always equal $HOME.& here: ~ is $HOME, but sometimes? & here: What is the “~/” directory? — slm, Oct 11 '14 at 07:11
Also if you'd read the Bash manual there's an entire section devoted to tilde-prefixes, which is what these are called: Bash Reference Manual - 3.5.2 Tilde Expansion — slm, Oct 11 '14 at 07:20

score 1 · Accepted Answer · answered Oct 11 '14 at 07:08

1

* is a metacharacter (or wildcard), all the other ones are tilde-prefix examples (~ is standard, ~+ and ~- are extensions).

None are variables so there is no point prefixing them with a $.

echo $~ works fine, it displays $~. There is no expansion because ~ is not used as a prefix.

for i in *; ... works as designed.

answered Oct 11 '14 at 07:08

jlliagre

61,204

1

Here they're discussed here in the Bash docs: http://www.gnu.org/software/bash/manual/html_node/Tilde-Expansion.html – slm Oct 11 '14 at 07:12

What are the types of ~, ~-, ~+, *?

1 Answers1