3.5.2 Tilde Expansion
If a word begins with an unquoted tilde character ('~'), all of the
characters up to the first unquoted slash (or all characters,
if there is no unquoted slash) are considered a tilde-prefix.
If none of the characters in the tilde-prefix are quoted, the
characters in the tilde-prefix following the tilde are treated as a
possible login name.
If this login name is the null string, the tilde is replaced with the
value of the HOME shell variable.
If HOME is unset, the home directory of the user executing the
shell is substituted instead.
Otherwise, the tilde-prefix is replaced with the home directory
associated with the specified login name.
If the tilde-prefix is '~+', the value of
the shell variable PWD replaces the tilde-prefix.
If the tilde-prefix is '~-', the value of the shell variable
OLDPWD, if it is set, is substituted.
If the characters following the tilde in the tilde-prefix consist of a
number N, optionally prefixed by a '+' or a '-',
the tilde-prefix is replaced with the
corresponding element from the directory stack, as it would be displayed
by the dirs builtin invoked with the characters following tilde
in the tilde-prefix as an argument (see section 6.8 The Directory Stack).
If the tilde-prefix, sans the tilde, consists of a number without a
leading '+' or '-', '+' is assumed.
If the login name is invalid, or the tilde expansion fails, the word is
left unchanged.
Each variable assignment is checked for unquoted tilde-prefixes immediately
following a ':' or '='.
In these cases, tilde expansion is also performed.
Consequently, one may use file names with tildes in assignments to
PATH, MAILPATH, and CDPATH,
and the shell assigns the expanded value.
The following table shows how Bash treats unquoted tilde-prefixes:
~
-
The value of
$HOME
~/foo
-
'$HOME/foo'
~fred/foo
-
The subdirectory
foo of the home directory of the user
fred
~+/foo
-
'$PWD/foo'
~-/foo
-
'${OLDPWD-'~-'}/foo'
~N
-
The string that would be displayed by 'dirs +N'
~+N
-
The string that would be displayed by 'dirs +N'
~-N
-
The string that would be displayed by 'dirs -N'
