# How to capture output of linux command **URL:** \ **Category:** Ruby\ **Created:** [April 9, 2010, 1:33pm UTC](https://www.ruby-forum.com/t/how-to-capture-output-of-linux-command/186600 "2010-04-09T13:33:41Z")\ **Posts on this page:** 8\ **Page:** 1
**Author:** ![ther](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/977dab/32.png) [@ther](https://www.ruby-forum.com/u/ther)\ **Post date:** [April 9, 2010, 1:33pm UTC](https://www.ruby-forum.com/t/how-to-capture-output-of-linux-command/186600/1 "2010-04-09T13:33:41Z")
You can run linux command: a = `ls /home` and receive output in variable a. But I would like /home to be variable. So I would invoke command like this: a = `"ls #{dir}"` This of course doesn’t work, but I hope you get the point. a = system(“ls #{dir}”) works, but returns only true or false not the standard output of command. How can I get standard output of the command and use variable as parameter? by TheR ---
**Author:** ![ther](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/977dab/32.png) [@ther](https://www.ruby-forum.com/u/ther)\ **Post date:** [April 9, 2010, 1:42pm UTC](https://www.ruby-forum.com/t/how-to-capture-output-of-linux-command/186600/2 "2010-04-09T13:42:13Z")
On Apr 9, 2010, at 04:33 , Damjan R. wrote: > a = `"ls #{dir}"` > > This of course doesn’t work, but I hope you get the point. remove the double quotes ---
**Author:** ![ther](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/977dab/32.png) [@ther](https://www.ruby-forum.com/u/ther)\ **Post date:** [April 9, 2010, 1:46pm UTC](https://www.ruby-forum.com/t/how-to-capture-output-of-linux-command/186600/3 "2010-04-09T13:46:31Z")
Damjan R. wrote: > You can run linux command: > > a = `ls /home` > > and receive output in variable a. > > But I would like /home to be variable. So I would invoke command like > this: > > a = `"ls #{dir}"` As Ryan said, you need to remove the double quotes. You’re asking the shell to execute the “ls whatever” command. There’s no such command. BTW, you actually want double quotes there, but put them around the parameter: a = `ls "#{dir}"` The purpose of the double quotes here is to protect against the case where the ‘dir’ variable contain spaces (which are meaningful to the shell --they separate tokens). ---
**Author:** ![ther](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/977dab/32.png) [@ther](https://www.ruby-forum.com/u/ther)\ **Post date:** [April 9, 2010, 1:50pm UTC](https://www.ruby-forum.com/t/how-to-capture-output-of-linux-command/186600/4 "2010-04-09T13:50:25Z")
Learn about Dir object. It has methods such as glob which should give you directory contents. Then you don’t have to care about stdout, nor quoting. [http://whynotwiki.com/Comparison\_of\_Escape\_class\_and\_String.shell\_escape](http://whynotwiki.com/Comparison_of_Escape_class_and_String.shell_escape) Have a look at the first example here Marc ---
**Author:** ![ther](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/977dab/32.png) [@ther](https://www.ruby-forum.com/u/ther)\ **Post date:** [April 9, 2010, 2:51pm UTC](https://www.ruby-forum.com/t/how-to-capture-output-of-linux-command/186600/5 "2010-04-09T14:51:54Z")
Excerpts from Albert S.'s message of Fri Apr 09 13:46:34 +0200 2010: > > > > The purpose of the double quotes here is to protect against the case > where the ‘dir’ variable contain spaces (which are meaningful to the > shell --they separate tokens). If we got hat route you want ls – ${dir} to protect against directories called “-a” or such … And keep in mind that directories may contain slashes and such stuff on linux. eg try mkdir a\b thus using quotes is not enough. It may work for most cases you use though. Anyway I’d do it right - you never know. Marc W. ---
**Author:** ![ther](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/977dab/32.png) [@ther](https://www.ruby-forum.com/u/ther)\ **Post date:** [April 9, 2010, 2:42pm UTC](https://www.ruby-forum.com/t/how-to-capture-output-of-linux-command/186600/6 "2010-04-09T14:42:32Z")
Marc W. wrote: > Learn about Dir object. It has methods such as glob which should give > you directory contents. Then you don’t have to care about stdout, nor > quoting. > > [http://whynotwiki.com/Comparison\_of\_Escape\_class\_and\_String.shell\_escape](http://whynotwiki.com/Comparison_of_Escape_class_and_String.shell_escape) > > Have a look at the first example here > > Marc Thanks guys. I used ls just as an example. I am actually calling smartctl command to find out SMART status of all disks on my computer. by TheR ---
**Author:** ![ther](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/977dab/32.png) [@ther](https://www.ruby-forum.com/u/ther)\ **Post date:** [April 9, 2010, 6:55pm UTC](https://www.ruby-forum.com/t/how-to-capture-output-of-linux-command/186600/7 "2010-04-09T18:55:56Z")
On Apr 9, 8:46 am, Albert S. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > ## The purpose of the double quotes here is to protect against the case where the ‘dir’ variable contain spaces (which are meaningful to the shell --they separate tokens). > > Posted viahttp://www.ruby-forum.com/. Keep in mind that `ls #{dir}` (without the quotes) is also DANGEROUS. What if you (or someone) set dir = “~; rm -rf ~”? BAD. So, using quotes is also safer. ---
**Author:** ![ther](https://www.ruby-forum.com/letter_avatar_proxy/v4/letter/t/977dab/32.png) [@ther](https://www.ruby-forum.com/u/ther)\ **Post date:** [April 12, 2010, 2:16am UTC](https://www.ruby-forum.com/t/how-to-capture-output-of-linux-command/186600/8 "2010-04-12T02:16:27Z")
Schneider wrote: > On Apr 9, 8:46�am, Albert S. [removed\_email\_address@domain.invalid](mailto:removed_email_address@domain.invalid) wrote: > > > ## The purpose of the double quotes here is to protect against the case where the ‘dir’ variable contain spaces (which are meaningful to the shell --they separate tokens). > > > > Posted viahttp://www.ruby-forum.com/. > > Keep in mind that `ls #{dir}` (without the quotes) is also DANGEROUS. > What if you (or someone) set dir = “~; rm -rf ~”? BAD. > > So, using quotes is also safer. No, using quotes isn’t safer: dir = ‘123" ; rm -rf ~ ; echo "’ `ls "#{dir}"` Results it doing ls “123” ; rm -rf ~ ; echo “”