Ruby Run Shell Command in a Specific Directory

Ruby run shell command in a specific directory

You can use the block-version of Dir.chdir. Inside the block you are in the requested directory, after the Block you are still in the previous directory:

Dir.chdir('mydir'){
  %x[#{cmd}]
}

How do I run commands in a given directory in Ruby?

try: Dir.chdir method. Reference: http://www.ruby-doc.org/core-2.1.0/Dir.html#method-c-chdir

Dir.chdir(directory) do
  run("bower install", capture: true, verbose: false)
end

The above example code will change to the directory represented by the directory variable, and then run whatever commands you pass to this block.

Running shell commands from a specific directory

Using Bash commands like pushd in Ruby is pointless, because those commands affect Bash's internal state of the Bash interpreter, and when you Run a shell command from Ruby using backticks or system, it creates a new subprocess, runs the command, and then closes that subprocess.

That means that even if you somehow manage to run pushd as a Bash command from Ruby, what will happen is that the the Bash subprocess will start, push the directory to the directory stack, and then exit. The changes you've made to the directory stack will be erased with all the other subprocess' data - and the next time you use a shell command you won't be at that directory.

You are scripting in Ruby, not in Bash - internal Bash commands have no meaning here, so you need to use the Ruby equivalents. For example, instead of writing:

system 'pushd /tmp'
system 'touch file_in_tmp'
system 'popd'

Which wouldn't work, what you want to do is:

Dir.chdir '/tmp' do
    system 'touch file_in_tmp'
end

How to call shell commands from Ruby

This explanation is based on a commented Ruby script from a friend of mine. If you want to improve the script, feel free to update it at the link.

First, note that when Ruby calls out to a shell, it typically calls /bin/sh, not Bash. Some Bash syntax is not supported by /bin/sh on all systems.

Here are ways to execute a shell script:

cmd = "echo 'hi'" # Sample string that can be used

Kernel#` , commonly called backticks – `cmd`
This is like many other languages, including Bash, PHP, and Perl.
Returns the result (i.e. standard output) of the shell command.
Docs: http://ruby-doc.org/core/Kernel.html#method-i-60
```
value = `echo 'hi'`
value = `#{cmd}`
```
Built-in syntax, %x( cmd )
Following the x character is a delimiter, which can be any character.
If the delimiter is one of the characters (, [, {, or <,
the literal consists of the characters up to the matching closing delimiter,
taking account of nested delimiter pairs. For all other delimiters, the
literal comprises the characters up to the next occurrence of the
delimiter character. String interpolation #{ ... } is allowed.
Returns the result (i.e. standard output) of the shell command, just like the backticks.
Docs: https://docs.ruby-lang.org/en/master/syntax/literals_rdoc.html#label-Percent+Strings
```
value = %x( echo 'hi' )
value = %x[ #{cmd} ]
```
Kernel#system
Executes the given command in a subshell.
Returns true if the command was found and run successfully, false otherwise.
Docs: http://ruby-doc.org/core/Kernel.html#method-i-system
```
wasGood = system( "echo 'hi'" )
wasGood = system( cmd )
```
Kernel#exec
Replaces the current process by running the given external command.
Returns none, the current process is replaced and never continues.
Docs: http://ruby-doc.org/core/Kernel.html#method-i-exec
```
exec( "echo 'hi'" )
exec( cmd ) # Note: this will never be reached because of the line above
```

Here's some extra advice:
$?, which is the same as $CHILD_STATUS, accesses the status of the last system executed command if you use the backticks, system() or %x{}.
You can then access the exitstatus and pid properties:

$?.exitstatus

For more reading see:

http://www.elctech.com/blog/i-m-in-ur-commandline-executin-ma-commands
http://blog.jayfields.com/2006/06/ruby-kernel-system-exec-and-x.html
http://tech.natemurray.com/2007/03/ruby-shell-commands.html

Call shell skript with specific working directory from R

As system2 uses shQuote we can only use system() and as already pointed out by @Dirk you can then use

system("cd ./sub && sh script.sh")

Ruby Run Shell Command in a Specific Directory