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Accepted
Alex
Asked: 2009-07-02 09:50:23 +0800 CST

Looping a command over a list of arguments in Linux

  • 772

How to execute the same command with arguments that are delivered by another command via pipe?

As a result of the extraction of file names from a source I get:

    $some_command
    filename1
    filename2
    filename3
    ...
    filenameN

I'd like to create files with these filenames with touch. How can I loop touch over these names?

linux pipe

5 Answers

  1. You can use xargs with -n1 to run a command once for each piped argument

    $some_command | xargs -n 1 touch

    In the case of touch however which accepts multiple arguments 

    touch `$some_command`

    will probably work for you.

    • 11
  2. Best Answer

    I only use for ... do ... done for very simple cases.

    For more complicated/dangerous scenarios:

    command | sed 's/^/touch /'

    This does nothing but prints intended commands. Review the results, then perform the same thing piping to sh -x (the -x flag is for debugging):

    command | sed 's/^/touch /' | sh -x
    • 7 
  3. for i in `$some_command`; do touch $i; done
    • 4

  4. If the filenames contain whitespace, then the following will work around them:

    some_command | while read filename ; do touch "$filename" ; done

    This will create files named:
    file name 1
    file name 2
    named file 3
    etc

    Assuming, of course, that it does produce those names.

    • 2

  5. "some_command | xargs touch" will probably do the trick, however there are two pitfalls:

    1. If a filename contains any whitespace character it will be treated as a separator, for example a filename "fuh bar" will, this way, be "touch"ed as a file named "fuh" and another one named "bar" instead of a single "fuh bar" one. To alleviate this you may check if your "some_command" is able to produce another delimiter, often NULL (see the "-print0" argument legit with the command "find"), and use the "--null" argument of xargs
    2. If the command does not produce anything xargs will fail miserably. Use its "--no-run-if-empty" argument
    • 1