new function __fish_preview_current_file to open file at the cursor in pager

bound to Alt+O by shared key bindings
created with help from @krobelus
fixes #6838

CHANGELOG.md

@@ -17,6 +17,7 @@
 
 #### New or improved bindings
 - New readline commands `undo` (Ctrl+_) and `redo` (Alt-/) can be used to revert changes to the command line or the pager search field (#6570).
+- New function `__fish_preview_current_file` (Alt+O) opens the current file at the cursor in a pager (#6838).
 
 #### Improved prompts
 - The default and example prompts print the correct exit status for commands prefixed with `not` (#6566).

doc_src/index.rst

@@ -1324,6 +1324,8 @@ Some bindings are shared between emacs- and vi-mode because they aren't text edi
 
 - :kbd:`Alt`\ +\ :kbd:`L` lists the contents of the current directory, unless the cursor is over a directory argument, in which case the contents of that directory will be listed.
 
+- :kbd:`Alt`\ +\ :kbd:`O` opens the file at the cursor in a pager.
+
 - :kbd:`Alt`\ +\ :kbd:`P` adds the string '``| less;``' to the end of the job under the cursor. The result is that the output of the command will be paged.
 
 - :kbd:`Alt`\ +\ :kbd:`W` prints a short description of the command under the cursor.

share/functions/__fish_preview_current_file.fish

@@ -0,0 +1,27 @@
+function __fish_preview_current_file --description "Open the file at the cursor in a pager"
+    set -l pager less --
+    set -q PAGER && echo $PAGER | read -at pager
+
+    # commandline -t will never return an empty list. However, the token
+    # could comprise multiple lines, so join them into a single string.
+    set -l file (commandline -t | string collect)
+
+    if test -z $file
+        # $backslash will parsed as regex which may need additional escaping.
+        set -l backslash '\\\\'
+        not status test-feature regex-easyesc && set backslash $backslash$backslash
+        set file (string replace -ra -- '([ ;#^<>&|()"\'])' "$backslash\$1" (commandline -oc)[-1])
+    end
+
+    set -q file[1] || return
+
+    # strip -option= from token if present
+    set file (string replace -r -- '^-[^\s=]*=' '' $file | string collect)
+
+    eval set -l files $file || return # Bail if $file does not tokenize.
+
+    if set -q files[1] && test -f $files[1]
+        $pager $files
+        commandline -f repaint
+    end
+end

share/functions/__fish_shared_key_bindings.fish

@@ -84,6 +84,7 @@ function __fish_shared_key_bindings -d "Bindings shared between emacs and vi mod
     bind --preset $argv \e. history-token-search-backward
 
     bind --preset $argv \el __fish_list_current_token
+    bind --preset $argv \eo __fish_preview_current_file
     bind --preset $argv \ew __fish_whatis_current_token
     # ncurses > 6.0 sends a "delete scrollback" sequence along with clear.
     # This string replace removes it.