diff --git a/lib/irb.rb b/lib/irb.rb
index a2a3a7190..677e63413 100644
--- a/lib/irb.rb
+++ b/lib/irb.rb
@@ -1036,6 +1036,9 @@ def eval_input
           rescue Interrupt, Exception => exc
             handle_exception(exc)
             @context.workspace.local_variable_set(:_, exc)
+            if statement.warning
+              warn statement.warning
+            end
           end
         end
       end
@@ -1102,24 +1105,52 @@ def each_top_level_statement
       end
     end
 
+    COMMAND_FLAG_REGEXP = /(?<cmd_flag>-[a-zA-Z]+( +\S+)*)/
+    COMMAND_ARG_REGEXP = /(?<cmd_arg>[^- ]\S*)/
+    COMMAND_NAME_REGEXP = /(?<cmd_name>\S+)/
+    SIMPLE_COMMAND_REGEXP = /^#{COMMAND_NAME_REGEXP}\z/
+    COMMAND_WITH_ARGS_REGEXP = /^#{COMMAND_NAME_REGEXP} +#{COMMAND_ARG_REGEXP}\z/
+    COMMAND_WITH_FLAGS_REGEXP = /^#{COMMAND_NAME_REGEXP} +#{COMMAND_FLAG_REGEXP}\z/
+    COMMAND_WITH_ARGS_AND_FLAGS_REGEXP = /^#{COMMAND_NAME_REGEXP} +#{COMMAND_ARG_REGEXP} +#{COMMAND_FLAG_REGEXP}\z/
+
+    COMMAND_REGEXP = Regexp.union(
+      SIMPLE_COMMAND_REGEXP,
+      COMMAND_WITH_ARGS_REGEXP,
+      COMMAND_WITH_FLAGS_REGEXP,
+      COMMAND_WITH_ARGS_AND_FLAGS_REGEXP
+    )
+
     def build_statement(code)
-      code.force_encoding(@context.io.encoding)
-      command_or_alias, arg = code.split(/\s/, 2)
-      # Transform a non-identifier alias (@, $) or keywords (next, break)
-      command_name = @context.command_aliases[command_or_alias.to_sym]
-      command = command_name || command_or_alias
-      command_class = ExtendCommandBundle.load_command(command)
-
-      if command_class
-        Statement::Command.new(code, command, arg, command_class)
+      code.force_encoding(@context.io.encoding) unless code.frozen?
+
+      possible_command_or_alias = code.split.first
+
+      possible_command_name = @context.command_aliases[possible_command_or_alias.to_sym]
+      possible_command_name = possible_command_name || possible_command_or_alias
+      command_class = ExtendCommandBundle.load_command(possible_command_name)
+
+      command_syntax_match = COMMAND_REGEXP.match(code.strip)
+
+      if command_class && command_syntax_match
+        arg = [command_syntax_match[:cmd_arg], command_syntax_match[:cmd_flag]].compact.join(' ')
+        Statement::Command.new(code, possible_command_name, arg, command_class)
       else
+        if command_class
+          warning_msg = <<~MSG
+            The input `#{code.strip}` was recognised as a Ruby expression, but it matched the name of the `#{possible_command_name}` command.
+            If you intended to run it as a command, please check if the syntax is correct.
+          MSG
+        end
+
         is_assignment_expression = @scanner.assignment_expression?(code, local_variables: @context.local_variables)
-        Statement::Expression.new(code, is_assignment_expression)
+        Statement::Expression.new(code, is_assignment_expression, warning: warning_msg)
       end
     end
 
     def single_line_command?(code)
-      command = code.split(/\s/, 2).first
+      command_match = COMMAND_REGEXP.match(code)
+      return unless command_match
+      command = command_match[:cmd_name]
       @context.symbol_alias?(command) || @context.transform_args?(command)
     end
 
diff --git a/lib/irb/cmd/ls.rb b/lib/irb/cmd/ls.rb
index 791b1c1b2..648afddf1 100644
--- a/lib/irb/cmd/ls.rb
+++ b/lib/irb/cmd/ls.rb
@@ -15,7 +15,7 @@ class Ls < Nop
       description "Show methods, constants, and variables. `-g [query]` or `-G [query]` allows you to filter out the output."
 
       def self.transform_args(args)
-        if match = args&.match(/\A(?<args>.+\s|)(-g|-G)\s+(?<grep>[^\s]+)\s*\n\z/)
+        if match = args&.match(/\A(?<args>.+\s|)(-g|-G)\s+(?<grep>[^\s]+)\s*\z/)
           args = match[:args]
           "#{args}#{',' unless args.chomp.empty?} grep: /#{match[:grep]}/"
         else
diff --git a/lib/irb/statement.rb b/lib/irb/statement.rb
index b12110600..4a7f4a7dc 100644
--- a/lib/irb/statement.rb
+++ b/lib/irb/statement.rb
@@ -2,7 +2,7 @@
 
 module IRB
   class Statement
-    attr_reader :code
+    attr_reader :code, :warning
 
     def is_assignment?
       raise NotImplementedError
@@ -21,9 +21,10 @@ def evaluable_code
     end
 
     class Expression < Statement
-      def initialize(code, is_assignment)
+      def initialize(code, is_assignment, warning: nil)
         @code = code
         @is_assignment = is_assignment
+        @warning = warning
       end
 
       def suppresses_echo?
@@ -66,6 +67,9 @@ def should_be_handled_by_debugger?
       end
 
       def evaluable_code
+        # Because measure command is used as a method, we need to treat it differently
+        return @code if @command == "measure"
+
         # Hook command-specific transformation to return valid Ruby code
         if @command_class.respond_to?(:transform_args)
           arg = @command_class.transform_args(@arg)
diff --git a/test/irb/test_debug_cmd.rb b/test/irb/test_debug_integration.rb
similarity index 94%
rename from test/irb/test_debug_cmd.rb
rename to test/irb/test_debug_integration.rb
index 0fb45af47..f7e770170 100644
--- a/test/irb/test_debug_cmd.rb
+++ b/test/irb/test_debug_integration.rb
@@ -6,7 +6,7 @@
 require_relative "helper"
 
 module TestIRB
-  class DebugCommandTest < IntegrationTestCase
+  class DebugIntegrationTest < IntegrationTestCase
     def setup
       super
 
@@ -434,5 +434,22 @@ def test_multi_irb_commands_are_not_available_after_activating_the_debugger
       assert_match(/irb\(main\):001> next/, output)
       assert_include(output, "Multi-IRB commands are not available when the debugger is enabled.")
     end
+
+    def test_locals_assignment_not_being_treated_as_debugging_command
+      write_ruby <<~'ruby'
+        binding.irb
+      ruby
+
+      output = run_ruby_file do
+        type "info = 4"
+        type "info + 1"
+        type "quit"
+      end
+
+      assert_match(/=> 5/, output)
+      # Since neither `info = <val>` nor `info + <val>` are debugging commands, debugger should not be activated in this
+      # session.
+      assert_not_match(/irb:rdbg/, output)
+    end
   end
 end
diff --git a/test/irb/test_irb.rb b/test/irb/test_irb.rb
index fb8b5c2bf..d407a2a09 100644
--- a/test/irb/test_irb.rb
+++ b/test/irb/test_irb.rb
@@ -58,6 +58,51 @@ def test_symbol_aliases_dont_affect_ruby_syntax
       assert_include output, "=> \"It's a foo\""
       assert_include output, "=> \"It's a bar\""
     end
+
+    def test_errored_input_that_match_a_command_raises_a_syntax_check_reminder
+      write_ruby <<~'RUBY'
+        class Foo
+        end
+        binding.irb
+      RUBY
+
+      errored_output = run_ruby_file do
+        type "show_source Foo bar"
+        type "exit!"
+      end
+
+      # The input should cause an error as it's evaluated as Ruby code
+      assert_include errored_output, 'undefined local variable or method `bar\''
+
+      # Because it starts with the name of a command, it should also raise a warning
+      assert_include errored_output,
+        'The input `show_source Foo bar` was recognised as a Ruby expression, but it matched the name of the `show_source` command.'
+      assert_include errored_output,
+        'If you intended to run it as a command, please check if the syntax is correct.'
+
+      output = run_ruby_file do
+        type "show_source Foo"
+        type "exit!"
+      end
+
+      # The input should work as a command
+      assert_include output, "From: #{@ruby_file.path}:1"
+      # Therefore, it should not raise a warning
+      assert_not_include output,
+        'If you intended to run it as a command, please check if the syntax is correct.'
+
+      output = run_ruby_file do
+        type "show_source = 'foo'"
+        type "show_source + 'bar'"
+        type "exit!"
+      end
+
+      # The input should work as Ruby code
+      assert_include(output, '=> "foobar"')
+      # Therefore, it should not raise a warning either
+      assert_not_include output,
+        'If you intended to run it as a command, please check if the syntax is correct.'
+    end
   end
 
   class IrbIOConfigurationTest < TestCase
@@ -738,4 +783,63 @@ def build_irb
       IRB::Irb.new(workspace, TestInputMethod.new)
     end
   end
+
+  class InputCategorisationTest < TestCase
+    def test_irb_distinguihes_commands_and_non_commands_correctly
+      irb = build_irb
+
+      [
+        "show_source Foo#bar",
+        "show_source Foo#bar -s",
+        "show_source Foo.bar",
+        "show_source Foo.bar -s",
+        "show_source == -s",
+        "show_source =~ -s",
+        "ls foo.bar -g baz",
+        "ls -g foo",
+        "bt 4",
+        "bt"
+      ].each do |input|
+        statement = irb.build_statement(input)
+        assert_equal(IRB::Statement::Command, statement.class, "Expected #{input} to be a command")
+      end
+
+      [
+        "info + 1",
+        "info - 1",
+        "info = 1",
+        "info = -1",
+        "info = /regex/",
+        "info = a",
+        "info += a",
+        "info -= a",
+        "info *= a",
+        "info &&= a",
+        "info ||= a",
+        "info # comment",
+        "info if foo",
+        "info ? foo : bar",
+        "info ; foo",
+        "info ,other = expr",
+        "info  -" # when an input is not a command nor Ruby code, we want to make it Ruby so it raises syntax error
+      ].each do |input|
+        statement = irb.build_statement(input)
+        assert_equal(IRB::Statement::Expression, statement.class, "Expected #{input} to not be a command")
+      end
+    end
+
+    private
+
+    def build_binding
+      Object.new.instance_eval { binding }
+    end
+
+    def build_irb
+      IRB.init_config(nil)
+      workspace = IRB::WorkSpace.new(build_binding)
+
+      IRB.conf[:VERBOSE] = false
+      IRB::Irb.new(workspace, TestInputMethod.new)
+    end
+  end
 end