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https://issues.apache.org/jira/browse/MESOS-3142?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
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Benjamin Hindman updated MESOS-3142:
------------------------------------
Shepherd: Benjamin Hindman
Sprint: Mesosphere Sprint 15
> As a Developer I want a better way to run shell commands
> --------------------------------------------------------
>
> Key: MESOS-3142
> URL: https://issues.apache.org/jira/browse/MESOS-3142
> Project: Mesos
> Issue Type: Story
> Components: stout
> Affects Versions: 0.23.0
> Reporter: Benjamin Hindman
> Assignee: Marco Massenzio
> Labels: mesosphere, tech-debt
>
> When reviewing the code in [r/36425|https://reviews.apache.org/r/36425/]
> [~benjaminhindman] noticed that there is a better abstraction that is
> possible to introduce for {{os::shell()}} that will simplify the caller's
> life.
> Instead of having to handle all possible outcomes, we propose to refactor
> {{os::shell()}} as follows:
> {code}
> /**
> * Returns the output from running the specified command with the shell.
> */
> Try<std::string> shell(const string& command)
> {
> // Actually handle the WIFEXITED, WIFSIGNALED here!
> }
> {code}
> where the returned string is {{stdout}} and, should the program be signaled,
> or exit with a non-zero exit code, we will simply return a {{Failure}} with
> an error message that will encapsulate both the returned/signaled state, and,
> possibly {{stderr}}.
> And some test driven development:
> {code}
> EXPECT_ERROR(os::shell("false"));
> EXPECT_SOME(os::shell("true"));
> EXPECT_SOME_EQ("hello world", os::shell("echo hello world"));
> {code}
> Alternatively, the caller can ask to have {{stderr}} conflated with
> {{stdout}}:
> {code}
> Try<string> outAndErr = os::shell("myCmd --foo 2>&1");
> {code}
> However, {{stderr}} will be ignored by default:
> {code}
> // We don't read standard error by default.
> EXPECT_SOME_EQ("", os::shell("echo hello world 1>&2"));
> // We don't even read stderr if something fails (to return in Try::error).
> Try<string> output = os::shell("echo hello world 1>&2 && false");
> EXPECT_ERROR(output);
> EXPECT_FALSE(strings::contains(output.error(), "hello world"));
> {code}
> An analysis of existing usage shows that in almost all cases, the caller only
> cares {{if not error}}; in fact, the actual exit code is read only once, and
> even then, in a test case.
> We believe this will simplify the API to the caller, and will significantly
> reduce the length and complexity at the calling sites (<6 LOC against the
> current 20+).
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