In the new mode (not yet enabled), universal variables are set by reading and writing the fishd file directly, with some file locking for synchronization. This enables forwards and backwards compatibility. However there is no compatibility with simultaneous edits. Changes may be lost if fishd and the new mechanisms both attempt writes.
fishd is still enabled by default for now; it will be disabled in a future commit. You can opt into the new mechanism (disabling fishd) by setting the environment variable fish_use_fishd to 0 before starting fish. This cannot itself be a universal variable, because of bootstrapping: the value is needed to determine how we read universal variables in the first place.
Universal variable change notifications (i.e. reacting immediately to live edits) are tricky. Checking for changes is simple and relatively inexpensive (just a stat()), but relying solely on that would require frequent wakeups, and show up in fs_usage. So how do we get change notifications into an fd that we can monitor via select()? We support a few strategies, expressed as universal_notifier_t::notifier_strategy_t. By default we use notifyd on OS X and a named pipe on Linux / everywhere else. This is also configurable at runtime via the fish_universal_notifier variable.
* use $XDG_CACHE_HOME for __fish_print_packages completion caches
* when starting fishd, redirect fishd output to /dev/null, not a
predictable path
Fix for CVE-2014-3219.
Closes#1440.
Currently it contains strange code like using `do` loop in order to
avoid `goto`s (they aren't evil, honestly), the pointless `if (mem)`
conditional which doesn't even work (had semicolon for some reason).
You may think this code had a bug where the code didn't check for
the pointer to be null before calling `free`, but this is not the case,
as according to C and C++ standard, `free` should allow `NULL` pointers,
and ignore them.
When you chroot in Debian, bash shows the chroot environment in the prompt:
```bash
...
if [ -z "${debian_chroot:-}" ] && [ -r /etc/debian_chroot ]; then
debian_chroot=$(cat /etc/debian_chroot)
fi
PS1='${debian_chroot:+($debian_chroot)}\u@\h:\w\$ '
...
```
This is the effect:
```
(chroot_env) user@host:~#
```
It is useful when chrooting, since usually the hostname remains the same and thus you can't distinguish where you are.
