Add --auto-sudo option and expand option documentation.

Using `sudo` within a script is generally considered poor practice, so
by default an error message is printed when the user attempts to perform
a write operation without sufficient permissions.

One way to deal avoid this error message is to alias `hosts` to `sudo
hosts`, but this then requires `sudo` for all operations and not just
write operations.

The new `--auto-sudo` option flag provides a way to automatically invoke
a write command with `sudo` when the user doesn't have write
permissions.

In order to provide cleaner documentation for this option, include more
option documentation in README.md.

README.md

@@ -54,6 +54,17 @@ Usage:
   hosts show (<ip> | <hostname> | <search string>)
   hosts remove (<ip> | <hostname> | <search string>) [--force]
   hosts unblock <hostname>
+  hosts --auto-sudo
+  hosts -h | --help
+  hosts --version
+
+Options:
+  --auto-sudo  Run write commands with `sudo` automatically.
+  -h --help    Display this help information.
+  --version    Display version information.
+
+Help:
+  hosts help [<command>]
 ```
 
 For full usage, run:
@@ -244,6 +255,29 @@ Description:
   Display the current program version.
 ```
 
+## Options
+
+### `--auto-sudo`
+
+When specified, all write operations that require `sudo` will automatically
+rerun the command using `sudo` when the current user does not have write the
+permissions to write to the hosts file.
+
+To have this option always enabled, add the following line to your shell
+configuration (`.bashrc`, `.zshrc`, or similar):
+
+```bash
+alias hosts="hosts --auto-sudo"
+```
+
+### `-h` `--help`
+
+Display help information.
+
+### `--version`
+
+Display version information.
+
 ## Tests
 
 To run the test suite, install [Bats](https://github.com/sstephenson/bats) and

hosts

@@ -224,6 +224,7 @@ _COMMAND_ARGV=("${0}")
 # on what the program needs.
 _CMD=""
 _USE_DEBUG=0
+_AUTO_SUDO=0
 
 while [ ${#} -gt 0 ]
 do
@@ -239,6 +240,9 @@ do
     --debug)
       _USE_DEBUG=1
       ;;
+    --auto-sudo|--sudo)
+      _AUTO_SUDO=1
+      ;;
     *)
       # The first non-option argument is assumed to be the command name.
       # All subsequent arguments are added to $_COMMAND_ARGV.
@@ -483,10 +487,16 @@ _present() {
 _verify_write_permissions() {
   if ! test -w "${HOSTS_PATH}"
   then
+    if ((_AUTO_SUDO))
+    then
+      sudo "${_ME}" "${_CMD}" "${_COMMAND_PARAMETERS[@]:-}"
+      exit $?
+    else
       _die printf \
 "You don't have permission to perform this operation. Try again with:
 sudo !!\n"
     fi
+  fi
 }
 
 ###############################################################################
@@ -608,10 +618,12 @@ Usage:
   ${_ME} show (<ip> | <hostname> | <search string>)
   ${_ME} remove (<ip> | <hostname> | <search string>) [--force]
   ${_ME} unblock <hostname>
+  ${_ME} --auto-sudo
   ${_ME} -h | --help
   ${_ME} --version
 
 Options:
+  --auto-sudo  Run write commands with \`sudo\` automatically.
   -h --help    Display this help information.
   --version    Display version information.
 
@@ -688,7 +700,7 @@ add() {
   _debug printf "add() \${2}: %s\n" "${2:-}"
   _debug printf "add() \${3}: %s\n" "${3:-}"
 
-  _verify_write_permissions
+  _verify_write_permissions "$@"
   local ip=${1:-}
   local hostname=${2:-}
   local comment=${*:3}
@@ -766,7 +778,7 @@ Description:
   search string.
 HEREDOC
 disable() {
-  _verify_write_permissions
+  _verify_write_permissions "$@"
   local search_string="${1}"
   if [[ -z "${search_string}" ]]
   then
@@ -832,7 +844,7 @@ Description:
   Open the ${HOSTS_PATH} file in your \$EDITOR.
 HEREDOC
 edit() {
-  _verify_write_permissions
+  _verify_write_permissions "$@"
   if [[ -z "${EDITOR}" ]]
   then
     _die printf "\$EDITOR not set.\n"
@@ -852,7 +864,7 @@ Description:
   or search string.
 HEREDOC
 enable() {
-  _verify_write_permissions
+  _verify_write_permissions "$@"
   local search_string="${1}"
   if [[ -z "${search_string}" ]]
   then
@@ -977,7 +989,7 @@ Description:
   IP and hostname pair will be removed.
 HEREDOC
 remove() {
-  _verify_write_permissions
+  _verify_write_permissions "$@"
   local is_search_pair=0
   local force_skip_prompt=0
   local arguments=()