A Perl 6 module to capture a command's output and exit code.
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Shell::Capture - capture a command's output and exit code


    use Shell::Capture;

    my Shell::Capture $c .= capture('id', '-u', '-n');
    if $c.exitcode != 0 {
        die "Could not execute id -u -n\n";
    } elsif $c.lines.elems != 1 {
        die "id -u -n returned something unexpected:\n" ~ $c.lines.join("\n") ~ "\n";
    say "Got my username: " ~ $c.lines[0];

    sub fail($r, @cmd) {
        die "fail with exit code $r.exitcode() and $r.lines().elems() " ~
            "line(s) of output and cmd " ~ @cmd;

    $c .= capture-check(:accept(0, 3), 'sh', '-c', 'date');
    say "The current date is $c.lines()[0]" if $c.exitcode == 0;

    $c .= capture-check(:accept(0, 3), 'sh', '-c', 'date; exit 3');
    say "The current date is $c.lines()[0]" if $c.exitcode == 3;

    $c .= capture-check(:accept(0, 3), :&fail, 'sh', '-c', 'date; exit 1');
    say 'not reached, fail() dies';


This class provides two methods to execute an external command, capture its output and exit code, and, in capture-check(), raise an error on unexpected exit code values.


  • exitcode

    Int:D $.exitcode

    The exit code of the executed external command.

  • lines

    Str:D @.lines

    The output of the external command split into lines with the newline terminator removed.


  • method capture()

    method capture(*@cmd)

    Execute the specified command in the same way as run() would, then create a new Shell::Capture object with its exitcode and lines members set respectively to the exit code of the command and its output split into lines, as described above.

  • method capture-check()

    method capture-check(:$accept, :$fail, *@cmd)

    Execute the specified command and create a Shell::Capture object in the same way as capture(), then check the exit code against the $accept list (default: only 0). If the exit code is on the list, return the Shell::Capture object to the caller.

    If the exit code is not on the list and there is no $fail handler specified, output an error message to the standard error stream and terminate the program. If a fail handler is specified, invoke it with two arguments: the Shell::Capture object for further examination and the command executed; if the fail handler returns, capture-check() will return the Shell::Capture object to its caller (useful for writing tests).


Peter Pentchev <roam@ringlet.net>


Copyright (C) 2016 Peter Pentchev


The Shell::Capture module is distributed under the terms of the Artistic License 2.0. For more details, see the full text of the license in the file LICENSE in the source distribution.