Bug #12467: Open mode 'a' does not work for Process.spawn on Windows

• Status: Third Party's Issue
• Assignee: -
• Target version: -
• ruby -v: ruby 2.3.0p0 (2015-12-25 revision 53290) [x64-mingw32]
• Backport: 2.1: UNKNOWN, 2.2: UNKNOWN, 2.3: UNKNOWN

[yhara (Yutaka HARA)]

Example:

spawn 'ruby -e "p Time.now"', [:out, :err] => ['log.txt', 'a']
sleep 1
spawn 'ruby -e "p Time.now"', [:out, :err] => ['log.txt', 'a']
sleep 1
p File.read('log.txt')

This program looks work correctly at first.

c:\>ruby spawn_bug.rb
"2016-06-07 18:47:25 +0900\n2016-06-07 18:28:17 +0900\n"

However, when I run it again, the log file is truncated like 'w' flag.

c:\>ruby spawn_bug.rb
"2016-06-07 18:47:38 +0900\n2016-06-07 18:28:17 +0900\n"

This is the same if I open the log file manually with File.open.

f = File.open('log.txt', 'a')
spawn 'ruby -e "p Time.now"', [:out, :err] => f
sleep 1
spawn 'ruby -e "p Time.now"', [:out, :err] => f
sleep 1
p File.read('log.txt')

I tried this on Windows 10. (Also confirmed this does not happen on Mac OS X 10.11 + ruby 2.2)

[nobu (Nobuyoshi Nakada)]

• Description updated (diff)
• Status changed from Open to Third Party's Issue

Windows does not provide append mode, but ruby emulates it.