I am designing a ruby program that needs to run a command and store it a variable.
var = exec('some command');
This doesn't work the way I want it to, it just prints the output from the command prompt and then ends the program.
So is there a function that doesn't end the program, doesn't print the cmd output and stores the information in a variable?
Thanks in advance.
You need to use either Ruby's built in backtick syntax, or use %x
output = `some command`
or
output = %x(some "command")
Open3 grants you access to stdin, stdout, stderr and a thread to wait
the child process when running another program. You can specify
various attributes, redirections, current directory, etc., of the
program as Process.spawn.
See the various ways of executing a command
Related
I have an input file called 0.in. To get the output I do ./a.out < 0.in in the Bash Shell.
Now, I have several such files (more than 500) and I want to automate this process using Python's subprocess module.
I tried doing this:
data=subprocess.Popen(['./a.out','< 0.in'],stdout=subprocess.PIPE,stdin=subprocess.PIPE).communicate()
Nothing was printed (data[0] was blank) when I ran this. What is the right method to do what I want to do?
Redirection using < is a shell feature, not a python feature.
There are two choices:
Use shell=True and let the shell handle redirection:
data = subprocess.Popen(['./a.out < 0.in'], stdout=subprocess.PIPE, shell=True).communicate()
Let python handle redirection:
with open('0.in') as f:
data = subprocess.Popen(['./a.out'], stdout=subprocess.PIPE, stdin=f).communicate()
The second option is usually preferred because it avoids the vagaries of the shell.
If you want to capture stderr in data, then add stderr=subprocess.PIPE to the Popen command. Otherwise, stderr will appear on the terminal or wherever python's error messages are being sent.
What I would like to do is:
run a ruby script...
that executes a shell command
and redirects it to a named pipe accessible outside the script
from the system shell, read from that pipe
That is, have the Ruby script capture some command output and redirect it in such a way that it's connectable to from outside the script?
I want to mention that the script cannot simply start and exit, since it's a REPL. The idea is that using the REPL you would be able to run a command and redirect its output elsewhere to consume it.
Using abort and an exit message, will pass the message to STDERR (and the script will fail with exit code 1). You can pass this shell command output in this way.
This is possibly not the only (or best) way, but it has worked for me in the past.
[edit]
You can also redirect the output to a file (using standard methods), and read that file outside the ruby script.
require 'open3'
stdin, stderr, status = Open3.capture3(commandline)
stdin.chomp #Here, you should ge
Incase, if someone wanted to use you can get the output via stdin.chomp
I want to run an executable from a ruby rake script, say foo.exe
I want the STDOUT and STDERR outputs from foo.exe to be written directly to the console I'm running the rake task from.
When the process completes, I want to capture the exit code into a variable. How do I achieve this?
I've been playing with backticks, process.spawn, system but I cant get all the behaviour I want, only parts
Update: I'm on Windows, in a standard command prompt, not cygwin
system gets the STDOUT behaviour you want. It also returns true for a zero exit code which can be useful.
$? is populated with information about the last system call so you can check that for the exit status:
system 'foo.exe'
$?.exitstatus
I've used a combination of these things in Runner.execute_command for an example.
backticks will get stdout captured into resulting string
foo.exe suggests you are running windows - do you have anything like cygwin installed? if you run your script within unixy shell you can do this:
result = `foo.exe 2>&1`
status = $?.exitstatus
quick googling says this should also work in native windows shell but i can't test this assupmtion
I'm trying this in ruby.
I have a shell script to which I can pass a command which will be executed by the shell after some initial environment variables have been set. So in ruby code I'm doing this..
# ruby code
my_results = `some_script -allow username -cmd "perform_action"`
The issue is that since the script "some_script" runs "perform_action" in it's own environment, I'm not seeing the result when i output the variable "my_results". So a ruby puts of "my_results" just gives me some initial comments before the script processes the command "perform_action".
Any clues how I can get the output of perform_action into "my_results"?
Thanks.
The backticks will only capture stdout. If you are redirecting stdout, or writing to any other handle (like stderr), it will not show up in its output; otherwise, it should. Whether something goes into stdout or not is not dependent on an environment, only on redirection or direct writing to a different handle.
Try to see whether your script actually prints to stdout from shell:
$ some_script -allow username -cmd "perform_action" > just_stdout.log
$ cat just_stdout.log
In any case, this is not a Ruby question. (Or at least it isn't if I understood you correctly.) You would get the same answer for any language.
I want to write a ruby program that could inspect the variable value of a program by launch the gdb and then print that value. How could I achieve this?
If I were in the shell, I would do this :
shell > gdb test
[...gbd started]
(gdb) p variable
$1 = 20
(gdb)
I also like to hear other ways that can achieve the same goal, not necessaliy to use gdb.
Try open4, which allows you to open stdin, stdout, stderr to an arbitrary command. You could use open4 to run gdb exactly as you describe, I have done this personally and it works quite nicely. Might want to create a wrapper class that handles running commands and returning status, as open4 just gives you file handles.