How to get ~/foo from /home/user1/foo?

Question

The Bash prompt supports the \w escape sequence, documented as

\w     the current working directory, with $HOME abbreviated
       with a tilde (uses the value of the PROMPT_DIRTRIM variable)

Is there any way to get a similar abbreviation for an arbitrary string? That is, is there a general command that does something like the following, provided that HOME=/home/user1

/home/user1         → ~
/home/user1/a/1     → ~/a/1
/home/user2/b/2     → ~user2/b/2
/root               → ~root

Sure, I could try something ugly with sed, but that is unlikely to give me the result I want in any case. :-)

The movitation behind this is that I would like to keep the titles in the tabs of my terminals as short as possible, hence abbreviate working directories where possible.

UPDATE: As there doesn’t appear to be a satisfactory solution easily available, and I would like to keep things sufficiently fast, I now went with a simple

pwd | sed -e "s|/root|~root|" -e "s|/home/user1|~|

and something similar for root. As I am the only user on the machine, this currently works more or less. I will keep the question open in case someone comes up with magical-tool-that-solves-all-problems (ideally not written in elisp…).

Answer 1

For your own home directory, use dir="${PWD/#$HOME/~}".

To just strip /home/ as glenn suggests, also use dir="${dir/#\/home\//~}".

---

Converting other users' homedirs is much more complicated, since you have to list all users every time.

• You can't even stop on the first match, since the few first accounts have a homedir of / which will always match. Instead, it is needed to check the longest prefix, which isn't simple.

• I often work with servers configured to read user accounts from LDAP, which takes a whole second to list all accounts; meanwhile, Active Directory wouldn't even allow to see the entire list.

Answer 2

For current user, and a string stored in a variable called DIR, this will work: ${DIR/~/\~}

It replaces the expansion of ~, which is either the value of the $HOME variable or the current user's home directory, with a literal ~.