Bash only expands a ~ if it's the beginning of a word. You can see this between the following commands:

$ echo -extract=~/test

-extract=~/test



oli@bert:~$ echo -extract ~/test

-extract /home/oli/test

Bash looks for standalone ~ characters and ~/ for this substitution. No other combination or quoted version will work.

$HOME works because variable substitutions are more robust (the $ is a special character whereas ~ is very much less so):

$ echo Thisisastring${HOME}awrawr

Thisisastring/home/oliawrawr

While we're talking about ~, it actually has another couple of other substitution uses:

• ~+ the current working directory (read from $PWD)


• ~- the previous working directory (read from $OLDPWD)

As with plain ~, these can have additional paths tacked on the end, and again, these have to be the prefix to a word or Bash will ignore them.

You can read more about this in man bash | less -p ' Tilde'