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Incerteza
Asked: 2014-03-06 21:08:18 +0800 CST

Trying to figure out what the command mean

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Please explain me what does this command mean:

wget -qO- https://toolbelt.heroku.com/install-ubuntu.sh | sh
  1. wget - use wget to download something
  2. -qO- first argument is -q, but what does 0- mean? why does it have dash after it?
  3. | sh - something about pipe, but what exactly?

Yes, I read man wget.

command-line

3 Answers

  1. -q runs wget in quiet mode.

     -O file
       --output-document=file
           The documents will not be written to the appropriate files, but all
           will be concatenated together and written to file.  If - is used as
           file, documents will be printed to standard output, disabling link
           conversion.  (Use ./- to print to a file literally named -.)

    sh is the Bourne shell. There are several shells, of which Bourne is the old standard.

    Your command above is saying to run wget in quiet mode (-q) and because output (O) takes -, instead of providing a file as destination, documents will be printed to standard output, disabling link conversion. Then the use of pipe | starts sh.

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  2. -q
      --quiet
          Turn off Wget's output.

-O file
      --output-document=file
          The documents will not be written to the appropriate files, but all
          will be concatenated together and written to file.  If - is used as
          file, documents will be printed to standard output, disabling link
          conversion.  (Use ./- to print to a file literally named -.)

sh
      The shell is a command that reads lines from either a file or the terminal,
      interprets them, and generally executes other commands.

    The vertical line pipe character before the sh pipes the output from -O- (standard output to the terminal) to the sh command which says to execute the file that was downloaded in the terminal as a program, assuming that the file that was downloaded first has its permissions set to allow executing the file as a program.

    To set the permissions to allow executing a file as a program: right-click the file, select Properties to open the Properties popup window and in Properties select the Permissions tab,and put a check mark to the left of where it says: Allow executing file as program.

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  3. 
* wget:     The non-interactive network downloader

* -q (--quit):    Turn off Wget's output.

* -O file (--output-document=file):    The documents will not be written to the appropriate files, but all will be concatenated together and written to file.  If - is used as file, documents will be printed to standard output, disabling link conversion.  

* URL https://toolbelt.heroku.com/install-ubuntu.sh     wget [option]... [URL]...

* | Pipelines
    A  pipeline is a sequence of one or more commands separated by one of the control operators | or |&.  The
    format for a pipeline is:

           [time [-p]] [ ! ] command [ [|⎪|&] command2 ... ]

    The standard output of command is connected  via  a  pipe  to  the  standard  input  of  command2.


* sh  command interpreter (shell)

    In overall this command will just download the script called install-ubuntu.sh from the given URL and then pass to the pipeline to be as input to the next comand which is sh. Thus this will install and run the script called install-ubuntu.sh in single command.

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