[Haskell-cafe] how to expand ~ in a filepath

[Richard O'Keefe]

Where do you get the idea that Bash does not expand ~foo?
<transcript>
pc at Boole ~/Downloads
$ echo $SHELL
/bin/bash

pc at Boole ~/Downloads
$ echo ~pc
/home/pc

</transcript>
Bash Reference Manual section 3.5.2 begins with this paragraph:
<quote>
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 tilde expands
to the home directory of the user executing the shell instead.
Otherwise, the tilde-prefix is replaced with the home directory
associated with the specified login name.
</quote>
Section 2.6.1 of the POSIX.1 shell specification describes tilde
expansion, and very explicitly requires that
<quote>
 the characters in the tilde-prefix following the <tilde> shall be
treated as a possible login name from the user database
</quote>
so it actually *is* a standard.

In fact in something like
 pongpath=~foo:~bar:~ugh
*each* of the three tildes begins a multicharacter tilde prefix.

On Wed, 23 Jul 2025 at 00:18, Mig Mit <migmit at gmail.com> wrote:
>
> There is no “should” here. It might be what you want, but it's not a universal standard. In Bash, “~foo” is not expanded.
>
> Sent from my iPad
>
> > On 2025. Jul 22., at 15:13, Richard O'Keefe <raoknz at gmail.com> wrote:
> >
> > But it's not just ~/ that should be expanded.
> > All four of "~" "~/bar" "~foo" and "~foo/bar" should be expanded by a
> > tilde-expander.
> >
> >> On Tue, 22 Jul 2025 at 03:06, Brandon Allbery <allbery.b at gmail.com> wrote:
> >>
> >> There's also https://github.com/xmonad/xmonad-contrib/blob/master/XMonad/Prelude.hs#L135-L156 although it also does a few other things.
> >>
> >>> On Mon, Jul 21, 2025 at 7:57 AM Tristan Cacqueray via Haskell-Cafe <haskell-cafe at haskell.org> wrote:
> >>>
> >>>
> >>> Hello, unfortunately there is no "expandHomePath" or "realpath" helpers
> >>> in the standard libraries. Searching for "FilePath -> IO FilePath" in
> >>> hoogle shows an implementation in the hledger project:
> >>>  https://hackage-content.haskell.org/package/hledger-lib-1.43.2/docs/Hledger-Utils-IO.html#v:expandHomePath
> >>>
> >>> … which check if the path begins with "~/", and replace that with the
> >>> output of "getHomeDirectory"
> >>>
> >>> -Tristan
> >>>
> >>> On Mon, Jul 21, 2025 at 07:19 PICCA Frederic-Emmanuel wrote:
> >>>> Hello, I am trying to open and read the content of this kind of filepath.
> >>>>
> >>>> ~/debian/changelog
> >>>>
> >>>> So is there a prefered way to expand the ~ into the real $HOME.
> >>>>
> >>>> thanks for your help
> >>>>
> >>>> Frédéric
> >>>>
> >>>>
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> >>
> >>
> >> --
> >> brandon s allbery kf8nh
> >> allbery.b at gmail.com
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