share/: Use <? redirection

This is mostly used instead of `test -r foo && string match bar <foo`
or `set bar (cat foo 2>/dev/null)`.

In doing so it can avoid a weird race condition where the file changes
between the check and the use, and it can avoid an external process or
having to open the file twice.

However it can also cause more work to happen - if you do

```fish
if test -r file
   # do a lot of work with file
end
```

it might be prudent to keep doing that. In the cases here it's usually
just a few `string` calls, which would operate on nothing and so be
pretty quick.

share/functions/__fish_complete_groups.fish

@@ -6,6 +6,6 @@ function __fish_complete_groups --description "Print a list of local groups, wit
     else
         while read -l line
             string split -f 1,4 : -- $line | string join \t
-        end </etc/group
+        end <?/etc/group
     end
 end

share/functions/__fish_complete_user_ids.fish

@@ -1,7 +1,7 @@
 function __fish_complete_user_ids --description "Complete user IDs with user name as description"
     if command -sq getent
         getent passwd | string replace -f -r '^([[:alpha:]_][^:]*):[^:]*:(\d+).*' '$2\t$1'
-    else if test -r /etc/passwd
-        string replace -f -r '^([[:alpha:]_][^:]*):[^:]*:(\d+).*' '$2\t$1' </etc/passwd
+    else
+        string replace -f -r '^([[:alpha:]_][^:]*):[^:]*:(\d+).*' '$2\t$1' <?/etc/passwd
     end
 end

share/functions/__fish_complete_users.fish

@@ -10,8 +10,8 @@ function __fish_complete_users --description "Print a list of local users, with
     else if command -sq dscl
         # This is the "Directory Service command line utility" used on macOS in place of getent.
         command dscl . -list /Users RealName | string match -r -v '^_' | string replace -r ' {2,}' \t
-    else if test -r /etc/passwd
-        string match -v -r '^\s*#' </etc/passwd | while read -l line
+    else
+        string match -v -r '^\s*#' <?/etc/passwd | while read -l line
             string split -f 1,5 : -- $line | string join \t | string replace -r ',.*' ''
         end
     end

share/functions/__fish_print_hostnames.fish

@@ -18,10 +18,8 @@ function __fish_print_hostnames -d "Print a list of known hostnames"
         string split ' '
 
     # Print nfs servers from /etc/fstab
-    if test -r /etc/fstab
-        string match -r '^\s*[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}:|^[a-zA-Z\.]*:' </etc/fstab |
-            string replace -r ':.*' ''
-    end
+    string match -r '^\s*[0-9]{1,3}\.[0-9]{1,3}\.[0-9]{1,3}:|^[a-zA-Z\.]*:' <?/etc/fstab |
+    string replace -r ':.*' ''
 
     # Check hosts known to ssh.
     # Yes, seriously - the default specifies both with and without "2".
@@ -65,13 +63,11 @@ function __fish_print_hostnames -d "Print a list of known hostnames"
         function _recursive --no-scope-shadowing
             set -l paths
             for config in $argv
-                if test -r "$config" -a -f "$config"
-                    set paths $paths (
-                    # Keep only Include lines and remove Include syntax
-                    string replace -rfi '^\s*Include\s+' '' <$config \
-                    # Normalize whitespace
-                    | string trim | string replace -r -a '\s+' ' ')
-                end
+                set paths $paths (
+                # Keep only Include lines and remove Include syntax
+                string replace -rfi '^\s*Include\s+' '' <?$config \
+                # Normalize whitespace
+                | string trim | string replace -r -a '\s+' ' ')
             end
 
             set -l new_paths
@@ -117,9 +113,7 @@ function __fish_print_hostnames -d "Print a list of known hostnames"
 
     # Read all files and operate on their combined content
     for file in $known_hosts
-        if test -r $file
-            read -z <$file
-        end
+        read -z <?$file
     end |
         # Ignore hosts that are hashed, commented or @-marked and strip the key
         # Handle multiple comma-separated hostnames sharing a key, too.

share/functions/__fish_set_locale.fish

@@ -26,15 +26,13 @@ function __fish_set_locale
     # but we operate under the assumption that the locale can't include whitespace. Other whitespace
     # shouldn't concern us, but a quoted "locale.LANG=SOMETHING" as a value to something else might.
     # Here the last definition of a variable takes precedence.
-    if test -r /proc/cmdline
-        for var in (string match -ra 'locale.[^=]+=\S+' < /proc/cmdline)
-            set -l kv (string replace 'locale.' '' -- $var | string split '=')
-            # Only set locale variables, not other stuff contained in these files - this also
-            # automatically ignores comments.
-            if contains -- $kv[1] $LOCALE_VARS
-                and set -q kv[2]
-                set -gx $kv[1] (string trim -c '\'"' -- $kv[2])
-            end
+    for var in (string match -ra 'locale.[^=]+=\S+' <?/proc/cmdline)
+        set -l kv (string replace 'locale.' '' -- $var | string split '=')
+        # Only set locale variables, not other stuff contained in these files - this also
+        # automatically ignores comments.
+        if contains -- $kv[1] $LOCALE_VARS
+            and set -q kv[2]
+            set -gx $kv[1] (string trim -c '\'"' -- $kv[2])
         end
     end
 
@@ -54,18 +52,16 @@ function __fish_set_locale
     # full POSIX-shell script.
     set -l user_cfg_dir (set -q XDG_CONFIG_HOME; and echo $XDG_CONFIG_HOME; or echo ~/.config)
     for f in $user_cfg_dir/locale.conf /etc/locale.conf /etc/env.d/02locale /etc/sysconfig/i18n /etc/default/locale
-        if test -r $f
-            while read -l kv
-                set kv (string split '=' -- $kv)
-                if contains -- $kv[1] $LOCALE_VARS
-                    and set -q kv[2]
-                    # Do not set already set variables again - this makes the merging happen.
-                    if not set -q $kv[1]
-                        set -gx $kv[1] (string trim -c '\'"' -- $kv[2])
-                    end
+        while read -l kv
+            set kv (string split '=' -- $kv)
+            if contains -- $kv[1] $LOCALE_VARS
+                and set -q kv[2]
+                # Do not set already set variables again - this makes the merging happen.
+                if not set -q $kv[1]
+                    set -gx $kv[1] (string trim -c '\'"' -- $kv[2])
                 end
-            end <$f
-        end
+            end
+        end <?$f
     end
 
     # If we really cannot get anything, at least set character encoding to UTF-8.

share/functions/fish_command_not_found.fish

@@ -5,11 +5,8 @@
 # This has a "ID=" line that defines the exact distribution,
 # and an "ID_LIKE=" line that defines what it is derived from or otherwise like.
 # For our purposes, we use both.
-set -l os
-if test -r /etc/os-release
-    set os (string match -r '^ID(?:_LIKE)?\s*=.*' < /etc/os-release | \
+set -l os (string match -r '^ID(?:_LIKE)?\s*=.*' <?/etc/os-release | \
     string replace -r '^ID(?:_LIKE)?\s*=(.*)' '$1' | string trim -c '\'"' | string split " ")
-end
 
 function __fish_default_command_not_found_handler
     printf (_ "fish: Unknown command: %s\n") (string escape -- $argv[1]) >&2

share/functions/fish_git_prompt.fish

@@ -478,20 +478,20 @@ function __fish_git_prompt_operation_branch_bare --description "fish_git_prompt
     set -l total
 
     if test -d $git_dir/rebase-merge
-        set branch (cat $git_dir/rebase-merge/head-name 2>/dev/null)
-        set step (cat $git_dir/rebase-merge/msgnum 2>/dev/null)
-        set total (cat $git_dir/rebase-merge/end 2>/dev/null)
+        read branch <?$git_dir/rebase-merge/head-name
+        read step <?$git_dir/rebase-merge/msgnum
+        read total <?$git_dir/rebase-merge/end
         if test -f $git_dir/rebase-merge/interactive
             set operation "|REBASE-i"
         else
             set operation "|REBASE-m"
         end
     else
         if test -d $git_dir/rebase-apply
-            set step (cat $git_dir/rebase-apply/next 2>/dev/null)
-            set total (cat $git_dir/rebase-apply/last 2>/dev/null)
+            read step <?$git_dir/rebase-apply/next
+            read total <?$git_dir/rebase-apply/last
             if test -f $git_dir/rebase-apply/rebasing
-                set branch (cat $git_dir/rebase-apply/head-name 2>/dev/null)
+                read branch <?$git_dir/rebase-apply/head-name
                 set operation "|REBASE"
             else if test -f $git_dir/rebase-apply/applying
                 set operation "|AM"

share/functions/help.fish

@@ -79,8 +79,7 @@ function help --description 'Show help for the fish shell'
             #
             # We use this instead of xdg-open because that's useless without a backend
             # like wsl-open which we'll check in a minute.
-            if test -f /proc/version
-                and string match -riq 'Microsoft|WSL|MSYS|MINGW' </proc/version
+            if string match -riq 'Microsoft|WSL|MSYS|MINGW' <?/proc/version
                 and set -l cmd (command -s powershell.exe cmd.exe /mnt/c/Windows/System32/cmd.exe)
                 # Use the first of these.
                 set fish_browser $cmd[1]