I'm trying to obtain the current version of nginx in Ruby. I've tried all of these, and nothing seems to work:
a = `nginx -v`
puts a # ==> nil
a = `nginx -V`
puts a # ==> nil again
a = system('nginx -v')
puts a # ==> nil
Anybody know how I can obtain this data? Strange behaviour. Same for postgres and ruby work fine.
There are a handful of methods that can run system commands and all of them are working differently. For example `date` works different than system('date'). More here.
Also, some commands write to STDOUT, some to STDERR and, apparently nginx -v writes to STDERR. For this scenario there's another option which gives access to more info: Open3
require 'open3'
stdout, stderr, status = Open3.capture3("nginx -v")
# ["", "nginx version: nginx/1.21.6\n", #<Process::Status: pid 22253 exit 0>]
stdout, stderr, status = Open3.capture3("date")
# ["Sun Jan 30 12:55:29 EET 2022\n", "", #<Process::Status: pid 22264 exit 0>]
stdout, stderr, status = Open3.capture3("ruby -v")
["ruby 2.7.5p203 (2021-11-24 revision f69aeb8314) [arm64-darwin21]\n", "", #<Process::Status: pid 22571 exit 0>]
Related
This code is not working properly:
my_command = %x{java -version &>/dev/null}
if $? != 0
How do I see what the STDERR/STDOUT status code is?
I tried using puts:
puts "values ===> $? or or '$?' my_command or #{my_command} %x{echo $?}"
but it doesn't work.
Using %x or something equivalent is an easy way of doing this but doesn't give you a lot of control. Instead use the Open3 library and popen3:
require 'open3'
Open3.popen3("java", "-version") do |stdin, stdout, stderr, wait_thr|
version = stdout.chomp
status = wait_thr.value
end
To get the status code :
stdout = %x(ls -l)
exit_code = $?.exitstatus
and then
if exit_code == 0 then
puts "Success"
else
puts "Problem"
end
I'd like to programmatically check if someone has their SSH keys set up correctly for GitHub. I understand that I can use `ssh -T git#github.com` in Ruby. However, I'd like to keep the ssh output in a variable.
My current code is:
github_response = `ssh -T git#github.com`
unless github_response.start_with?('Hi')
puts 'Please set up your GitHub ssh keys'
end
`ssh -T git#github.com` outputs the response (starting with "Hi"). However the github_response variable is nil.
How can I assign the output of `ssh -T git#github.com` to github_response?
Your example failed because the Hi xxx! You've successfully authenticated.... message is not from stdout, but stderr.
> require 'open3'
=> true
> stdin, stdout, stderr, wait_thr = Open3.popen3('ssh -T git#github.com')
=> [#<IO:fd 8>, #<IO:fd 9>, #<IO:fd 11>, #<Thread:0x007f89ee1149a8 sleep>]
> stdout.gets
=> nil
> stderr.gets
=> "Hi halfelf! You've successfully authenticated, but GitHub does not provide shell access.\n"
You could add -v for verbose output, it will then dump much of the connection info to stdout. From that log you can scrape to find whether the server accepted any of the keys the ssh client offered
I have a bunch of system calls in ruby such as the following and I want to check their exit codes simultaneously so that my script exits out if that command fails.
system("VBoxManage createvm --name test1")
system("ruby test.rb")
I want something like
system("VBoxManage createvm --name test1", 0) <-- where the second parameter checks the exit code and confirms that that system call was successful, and if not, it'll raise an error or do something of that sort.
Is that possible at all?
I've tried something along the lines of this and that didn't work either.
system("ruby test.rb")
system("echo $?")
or
`ruby test.rb`
exit_code = `echo $?`
if exit_code != 0
raise 'Exit code is not zero'
end
From the documentation:
system returns true if the command gives zero exit status, false for
non zero exit status. Returns nil if command execution fails.
system("unknown command") #=> nil
system("echo foo") #=> true
system("echo foo | grep bar") #=> false
Furthermore
An error status is available in $?.
system("VBoxManage createvm --invalid-option")
$? #=> #<Process::Status: pid 9926 exit 2>
$?.exitstatus #=> 2
For me, I preferred use `` to call the shell commands and check $? to get process status. The $? is a process status object, you can get the command's process information from this object, including: status code, execution status, pid, etc.
Some useful methods of the $? object:
$?.exitstatus => return error code
$?.success? => return true if error code is 0, otherwise false
$?.pid => created process pid
system returns false if the command has an non-zero exit code, or nil if there is no command.
Therefore
system( "foo" ) or exit
or
system( "foo" ) or raise "Something went wrong with foo"
should work, and are reasonably concise.
You're not capturing the result of your system call, which is where the result code is returned:
exit_code = system("ruby test.rb")
Remember each system call or equivalent, which includes the backtick-method, spawns a new shell, so it's not possible to capture the result of a previous shell's environment. In this case exit_code is true if everything worked out, nil otherwise.
The popen3 command provides more low-level detail.
One way to do this is to chain them using and or &&:
system("VBoxManage createvm --name test1") and system("ruby test.rb")
The second call won't be run if the first fails.
You can wrap those in an if () to give you some flow-control:
if (
system("VBoxManage createvm --name test1") &&
system("ruby test.rb")
)
# do something
else
# do something with $?
end
Ruby 2.6 added option to raise exception in Kernel#system:
system("command", exception: true)
I want something like
system("VBoxManage createvm --name test1", 0) <-- where the second parameter checks the exit code and confirms that that system call was successful, and if not, it'll raise an error or do something of that sort.
You can add exception: true to your system call to have an error raised on non 0 exit codes.
For example, consider this small wrapper around system which prints the command (similar to bash -x, fails if there's a non 0 exit code (like bash -e) and returns the actual exit code:
def sys(cmd, *args, **kwargs)
puts("\e[1m\e[33m#{cmd} #{args}\e[0m\e[22m")
system(cmd, *args, exception: true, **kwargs)
return $?.exitstatus
end
To be called like: sys("hg", "update")
If you want to call a program that uses a different convention for exit codes, you can suppress raising the exception:
sys("robocopy", src, dst, "/COPYALL", "/E", "/R:0", "/DCOPY:T", exception: false)
You can also suppress stdout and stderr for noisy programs:
sys("hg", "update", "default", :out => File::NULL, :err => File::NULL)
I'm using IO.popen to start a subprocess, but I only get the result of everything that happened in the time it took for the subprocess to run (sometimes 5 minutes or whatever) when the subprocess exits. I really need to be able to see everything the subprocess writes to stderr and stdout as-and-when it happens.
So far I could not find anything that works like this, but I'm sure it's possible.
if you need to get output in real time i would recommend to use stdlib PTY instead of popen
something like this:
require 'pty'
cmd = 'echo a; sleep 1; cat /some/file; sleep 1; echo b'
PTY.spawn cmd do |r, w, pid|
begin
r.sync
r.each_line { |l| puts "#{Time.now.strftime('%M:%S')} - #{l.strip}" }
rescue Errno::EIO => e
# simply ignoring this
ensure
::Process.wait pid
end
end
exit "#{cmd} failed" unless $? && $?.exitstatus == 0
> 33:36 - a
> 33:37 - cat: /some/file: No such file or directory
> 33:38 - b
this way you get output instantly, just as in terminal
You might want to use Open3.popen3 from standard library, it gives access to stdin, stdout, and stderr as streams.
When I do something like the following:
output = `identify some_file`
output == "Output of identify"
But when...
output = `identify non_existant_file`
output != "Error output of identify"
How can I get the error output of system calls?
I found out the answer. The output is being sent to stderr. So I can just add the following at the end of the command to redirect stderr to stdout:
output = `identify any_file 2>&1`
output == "Error or output of identify"
Here is the explanation of this witchcraft
You may use Open3.popen3.
http://www.ruby-doc.org/stdlib-1.9.3/libdoc/open3/rdoc/Open3.html#method-c-popen3
popen3(*cmd, &block) click to toggle source
Open stdin, stdout, and stderr streams and start external executable.
Open3.popen3([env,] cmd... [, opts]) {|stdin, stdout, stderr, wait_thr|
pid = wait_thr.pid # pid of the started process.
...
exit_status = wait_thr.value # Process::Status object returned.
}