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README.md

README.md

Introduction

Proc::Feed provides a couple wrappers for Proc::Async that are more convenient to use than the run and shell subs. Specifically, these wrappers let you easily feed data to them and also from them to other callables using the feed operator (==> or <==).


sub proc

sub proc(
    \command where Str:D|List:D,
    $input? is raw,

    Bool :$check = True,
    Bool :$bin,    # only applies to input.

    :$stderr where Any|Callable:D|Str:D|IO::Handle:D,

    :$shell where Bool:D|Str:D = False,

    :$cwd = $*CWD,
    Hash() :$env = %*ENV,

    :$scheduler = $*SCHEDULER

) is export(:DEFAULT, :proc);

Use the proc sub to run a command when you don't need to capture its output(STDOUT):

    proc <<ls -la "READ ME.txt">>;

Here we passed a list, of which the first element is the executable, while the rest are arguments passed to the executable.

NOTE: proc blocks until the external command is completed and returns a Proc object, which when sunk throws an exception if the command exited with a non-zero status.

It's also possible to redirect STDERR if desired:

    # Redirect STDERR to /dev/null
    proc <ls whatever>, :stderr('/dev/null/');

    # Same thing; but with a file we opened
    my $black-hole = open('/dev/null', :w);
    proc <ls whatever>, :stderr($black-hole);
    $black-hole.close;

    # Same effect that ignores error messages; this time, with a callable
    # that just ignores the lines from STDERR.
    proc <ls whatever>, :stderr({;});

Sometimes it can be convenient to run a command via a shell (defaults to /bin/bash) if you need to use the features (e.g., globbing, I/O redirection, ... etc) it provides:

    proc(['ls -la ~/.*'], :shell);

One can also simply pass a single string (recommended when using :shell) instead of a list if not passing any arguments to the command from Perl 6:

    proc('ls -la ~/.*', :shell);

However, if a list is passed, any remaining elements of the list are passed to the shell as positional arguments, which will be available as $1, $2, ..., and so on, in the shell command/script:

    proc(['md5sum "$1" | cut -d" " -f1 > "$1.md5"', "$*PROGRAM"], :shell);

    # ~/.* is not expanded here because it will be passed as an argument to bash.
    proc(<<ls -la ~/.*>>, :shell);  # runs:  bash -c 'ls' - bash '-la' '~/.*'

    # prints an empty line
    proc(<<echo hello world>>, :shell)

    # prints hello world
    proc(<<'echo "$@"' hello world>>, :shell)

    # prints the passed args; also shows you can specify the shell to use.
    proc([q:to/EOF/, 'arg1', 'arg2'], :shell</usr/local/bin/bash>);
    echo "Using SHELL - $0"
    echo "First argument is: $1"
    echo "Second argument is: $2"
    EOF

sub capture

sub capture(
    \command where Str:D|List:D,
    $input? is raw,

    Bool :$check = True,
    Bool :$chomp = True,
    Bool :$merge,
    Bool :$bin,    # only applies to input.

    :$stderr where Any|Callable:D|Str:D|IO::Handle:D,

    :$shell where Bool:D|Str:D = False,

    Str:D :$enc = 'UTF-8',
    Bool :$translate-nl = True,

    :$cwd = $*CWD,
    Hash() :$env = %*ENV,

    :$scheduler = $*SCHEDULER

    --> Str:D

) is export(:DEFAULT, :capture);

To capture the STDOUT of a command use the capture sub, which returns a Str:D instead of a Proc:

    capture(<<md5sum "$*PROGRAM">>).split(' ')[0] ==> spurt("$*PROGRAM.md5");

    # You can still run command via a shell
    my $ls = capture('ls -la ~/.*', :shell);

    my $err = capture(<<ls -la "doesn't exist">>, :merge);
    #
    # :merge redirects STDERR to STDOUT, so error messages are also
    # captured in this case.

NOTE: By default, similar to command substitution in Bash, any trailing newline of the captured output is removed. You can disable this behavior by specifying :!chomp.

NOTE: If the command run by capture fails with a non-zero exit status, an exception will be thrown. You can disable this behavior with :!check, and in which case, an empty string will be returned if the command fails.

You can easily feed iterable inputs to a capture: (you can do the same with proc or pipe too):

    my $data = slurp("$*HOME/.bashrc");
    my $chksum = ($data ==> capture('md5sum')).split(' ')[0];

By default, both input and output are assumed to be lines of strings, but you can specify both to be binary with :bin, or only one of which to be binary with either :bin<IN> or :bin<OUT>:

NOTE: For capture and proc, only :bin and :!bin are possible, and both apply only to STDIN.

    # Binary (Blob) in; string (Str) out.
    my $blob = Blob.new(slurp("/bin/bash", :bin));
    my $chksum = ($blob ==> capture('md5sum', :bin)).split(' ')[0];

    # String (Str) in; binary (Blob) out.
    # See below for more details on using 'run' and 'pipe'.
    run {
        my $f = "$*HOME/.bashrc";
        my $gzipped = open("$f.gz", :w:bin);
        LEAVE $gzipped.close;
        slurp($f) \
        ==> pipe(<gzip -c>, :bin<OUT>)
        ==> each { spurt $gizpped, :bin }
    }

NOTE: It makes no sense to feed from a proc (i.e., proc(…) ==> …) because proc(…) returns a Proc, which is not iterable.


sub pipe

sub pipe(
    \command where Str:D|List:D,
    $input? is raw,

    Bool :$chomp is copy,

    :$bin where {
        $_ ~~ Bool:D|'IN'|'OUT' and (
            # if :bin or :bin<OUT> then :chomp shouldn't be specified.
            ! ($_ eq 'OUT' || ($_ ~~ Bool && $_))
            || !$chomp
        )
    } = False,

    :$stderr where Any|Callable:D|Str:D|IO::Handle:D,

    Bool :$merge,

    Str:D :$enc = 'UTF-8',
    Bool :$translate-nl = True,

    :$cwd = $*CWD,
    Hash() :$env = %*ENV,

    :$shell where Bool:D|Str:D = False,

    :$scheduler = $*SCHEDULER

) is export(:DEFAULT, :pipe);

Finally, pipe returns an iterable of the output from the STDOUT of the external process, so you can feed it to another callable. By default, text output is assumed and the output is an iterable of lines. If binary output is specified, then the output will be an iterable of Blob's.

pipe should be used within a Block passed to the run sub, which returns the result returned by the block:

    # Example
    my $chksum = run {
        slurp("/bin/bash", :bin) \
        ==> pipe('gzip', :bin)
        ==> capture('md5sum', :bin<IN>)
        ==> split(' ')
        ==> *.[0]()
    }

    # Example
    run {
        my $tarball = open("./somedir.tgz", :w);
        LEAVE $tarball.close;
        pipe(«ssh my.remote-host.com "tar -czf - ./somedir"», :bin) \
        ==> each { spurt $tarball, $_ }
    }

    # Example
    my $total = run {
        [+] (pipe(«find /var/log/ -f») ==> map(*.IO.s))
    } 

You must extract the data you want in the run block because run terminates all external processes started by pipe's at the end of the block by sending them the SIGCHLD signal.

NOTE: Subs like map and grep are lazy by default, so they are not suitable to be used at the end of a pipeline, unless you also consume the entire pipeline with somethig like the [+] operator in the above example. To consume a pipeline, you can also assign or feed the pipeline to an array, or listify the pipeline by using a ==> @ at the end of the pipeline.

By default, run throws a BrokenPipeline exception if any of the pipe calls fails or exits with non-zero status, or if an exception is propagated from the block. You can prevent an exception from being thrown with the :!check option of run, in which case it returns a two-element list instead:

    my ($result, $err) = run :!check, {
        pipe(<<cat "$*HOME/.bashrc">>) \
        ==> pipe(<gunzip -c>)  # <-- fails because input is not gzipped
        ==> join('')
    }
    if $err {
        put 'Failed decompressing file...';
        say $err;   # $err.gist will show you the errors and stack traces.
    } else {
        put $result;
    }

The first item is the return value of the block you passed to run; the second item is a BrokenPipeline exception object if there's any.

NOTE: Many code snippets in this doc are made to demo how the various functions from this module can be used. They are usually not the most efficient way to do the same thing if data have to flow from an external process to Perl 6, without any processing, just to flow back to another external process. For example, with run { pipe(<<ls -la>>) ==> proc('nl') } this module currently is not smart enough to connect the STDOUT of the first process to the STDIN of the second process, and therefore the data have to go through Perl 6.

Other helpers

sub each(&code, $input? is raw) is export(:each);
multi sub map(Range \range, &code, $input? is raw) is export(:map);

each, often used for side effects, makes feeding into a block that just wants to be called for each item of the iterable fed to it easier:

# using each:
(1,2,3,4) ==> each { .say }

# without each:
(1,2,3,4) ==> { .say for $_ }()

The map multi sub exported by this module takes a Range parameter so that you can limit the code to only a certain range of input a block:

# using ranged map:
1,1, * + * ... Inf ==> map ^10, { $_ ** 2 }

# without ranged map:
1,1, * + * ... Inf ==> { gather for $_[^10] { take $_ ** 2 } }()
sub quote(Str $s --> Str) is export(:quote);

quote will single-quote a string so that it can be used in a shell script/command literally:

my $file = q/someone's file is > than 1GB/;
put capture("echo {quote $file}", :shell);
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