5

Here is the command in question

 find . -name "*.txt" | xargs -Ifile sh -c 'echo $(basename $1) ' -- file

So without the double dash the file is not passed to sh and then get recognized as $1. Why is that? I know that -- prevents the consequent argument from being recognized as command line options. But since file is not prepended with a dash, it seems as though there is no reason for it to get recognized as a command line option.

8

The first non-option argument to sh becomes $0. When sh is invoked on a script, that's the path to the script. When you run sh -c SOMECOMMAND, the shell doesn't use the argument for anything apart from placing into $0. Conventionally, it would be a name for the script passed to -c, by analogy with the sh /path/to/script case where $0 is the name or path of the script.

Unlike most commands, -- is treated as an ordinary argument, not as a special-purpose marker. So it's really -- that's used as $0 and not the next argument.

$ sh -c 'echo $1' hello            

$ sh -c 'echo $0' hello
hello
$ sh -c 'echo $0; echo $1' hello world
hello
world
$ sh -c 'echo $0; echo $1' -- hello
--
hello

This has nothing to do with xargs, it's passing all of the arguments after sh to the sh command.

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  • What's the "name" here? – Melab Sep 19 '17 at 20:23
  • @Melab I meant the argument. It's conventionally a name for the -c script. I've edited my answer. – Gilles 'SO- stop being evil' Sep 20 '17 at 8:52
0

In the above example the -- is acting as a blocker between sh -c 'echo $(basename $1) ' and file. it's forcing the string file to be the $1 argument to sh.

The above could've been streamlined to this:

$ find . -name "*.txt" | xargs -Ifile sh -c 'echo $(basename file) '
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