Capistrano & Bash: ignore command exit status - ruby-on-rails

Question

I'm using Capistrano run a remote task. My task looks like this:
task :my_task do
run "my_command"
end
My problem is that if my_command has an exit status != 0, then Capistrano considers it failed and exits. How can I make capistrano keep going when exit when the exit status is not 0? I've changed my_command to my_command;echo and it works but it feels like a hack.

Answer 1

The simplest way is to just append true to the end of your command.
task :my_task do
run "my_command"
end
Becomes
task :my_task do
run "my_command; true"
end

Answer 2

For Capistrano 3, you can (as suggested here) use the following:
execute "some_command.sh", raise_on_non_zero_exit: false

Answer 3

The +grep+ command exits non-zero based on what it finds. In the use case where you care about the output but don't mind if it's empty, you'll discard the exit state silently:
run %Q{bash -c 'grep #{escaped_grep_command_args} ; true' }
Normally, I think the first solution is just fine -- I'd make it document itself tho:
cmd = "my_command with_args escaped_correctly"
run %Q{bash -c '#{cmd} || echo "Failed: [#{cmd}] -- ignoring."'}

Answer 4

You'll need to patch the Capistrano code if you want it to do different things with the exit codes; it's hard-coded to raise an exception if the exit status is not zero.
Here's the relevant portion of lib/capistrano/command.rb. The line that starts with if (failed... is the important one. Basically it says if there are any nonzero return values, raise an error.
# Processes the command in parallel on all specified hosts. If the command
# fails (non-zero return code) on any of the hosts, this will raise a
# Capistrano::CommandError.
def process!
loop do
break unless process_iteration { #channels.any? { |ch| !ch[:closed] } }
end
logger.trace "command finished" if logger
if (failed = #channels.select { |ch| ch[:status] != 0 }).any?
commands = failed.inject({}) { |map, ch| (map[ch[:command]] ||= []) << ch[:server]; map }
message = commands.map { |command, list| "#{command.inspect} on #{list.join(',')}" }.join("; ")
error = CommandError.new("failed: #{message}")
error.hosts = commands.values.flatten
raise error
end
self
end

Answer 5

I find the easiest option to do this:
run "my_command || :"
Notice: : is the NOP command so the exit code will simply be ignored.

Answer 6

I just redirect STDERR and STDOUT to /dev/null, so your
run "my_command"
becomes
run "my_command > /dev/null 2> /dev/null"
this works for standard unix tools pretty well, where, say, cp or ln could fail, but you don't want to halt deployment on such a failure.

Answer 7

I not sure what version they added this code but I like handling this problem by using raise_on_non_zero_exit
namespace :invoke do
task :cleanup_workspace do
on release_roles(:app), in: :parallel do
execute 'sudo /etc/cron.daily/cleanup_workspace', raise_on_non_zero_exit: false
end
end
end
Here is where that feature is implemented in the gem.
https://github.com/capistrano/sshkit/blob/4cfddde6a643520986ed0f66f21d1357e0cd458b/lib/sshkit/command.rb#L94