[ruby/irb] Support disabling pager

(https://github.com/ruby/irb/pull/783)

With either `IRB.conf[:USE_PAGER] = false` or `--no-pager` commnad line flag.

I decided use `--no-pager` instead of `--use-pager` because it matches with
Pry and git's command line flags.

https://github.com/ruby/irb/commit/df1c3b9042

3 files changed, 5 insertions, 1 deletions

diff --git a/lib/irb/init.rb b/lib/irb/init.rb
index 4df285ce64..9704e36cb1 100644
--- a/lib/irb/init.rb
+++ b/lib/irb/init.rb
@@ -82,6 +82,7 @@ module IRB # :nodoc:
     @CONF[:USE_LOADER] = false
     @CONF[:IGNORE_SIGINT] = true
     @CONF[:IGNORE_EOF] = false
+    @CONF[:USE_PAGER] = true
     @CONF[:EXTRA_DOC_DIRS] = []
     @CONF[:ECHO] = nil
     @CONF[:ECHO_ON_ASSIGNMENT] = nil
@@ -285,6 +286,8 @@ module IRB # :nodoc:
         end
       when "--noinspect"
         @CONF[:INSPECT_MODE] = false
+      when "--no-pager"
+        @CONF[:USE_PAGER] = false
       when "--singleline", "--readline", "--legacy"
         @CONF[:USE_SINGLELINE] = true
       when "--nosingleline", "--noreadline"
diff --git a/lib/irb/lc/help-message b/lib/irb/lc/help-message
index c7846b755d..37347306e8 100644
--- a/lib/irb/lc/help-message
+++ b/lib/irb/lc/help-message
@@ -22,6 +22,7 @@ Usage:  irb.rb [options] [programfile] [arguments]
                     Show truncated result on assignment (default).
   --inspect         Use 'inspect' for output.
   --noinspect       Don't use 'inspect' for output.
+  --no-pager        Don't use pager.
   --multiline       Use multiline editor module (default).
   --nomultiline     Don't use multiline editor module.
   --singleline      Use single line editor module.
diff --git a/lib/irb/pager.rb b/lib/irb/pager.rb
index 119515078b..e38d97e3c7 100644
--- a/lib/irb/pager.rb
+++ b/lib/irb/pager.rb
@@ -18,7 +18,7 @@ module IRB
       end
 
       def page
-        if STDIN.tty? && pager = setup_pager
+        if IRB.conf[:USE_PAGER] && STDIN.tty? && pager = setup_pager
           begin
             pid = pager.pid
             yield pager