Hi Nick,
Thanks for this survey of other languages, it’s very useful.
I think if we were to add something, I would prefer to keep it simple. Just one
class method on Process which is a fairly straightforward wrapper of the other
functionality already there.
I was thinking of perhaps a completion handler version, with the expectation
that once async/await style completions land it would be pretty easy to use in
a kind of straight-line mechanism.
- Tony
> On Nov 20, 2017, at 4:37 AM, Nick Keets <nick.ke...@gmail.com> wrote:
>
> Looking at what Python (subprocess) and Go (os.exec) do, it looks like they
> agree on the following:
> - executable and arguments are merged in one array
> - they don't require full path for the executable
> - they don't expand tildes
> - blocking calls are the default
> - they are more explicit about stdin, stdout, stderr
>
> Some example scenarios based on that, with possible swift code:
>
> 1) Run a command and ignore output
>
> Python:
> subprocess.run(["sleep", "1"], stdout=subprocess.DEVNULL,
> stderr=subprocess.DEVNULL)
>
> Go:
> cmd := exec.Command("sleep", "1")
> err := cmd.Run()
>
> Possible Swift:
> try Process.run(["sleep", "1"])
>
>
> 2) Run a command and capture stdout
>
> Python:
> out = subprocess.check_output(["ls", "-l"])
>
> Go:
>
> cmd := exec.Command("ls", "-l")
> out, err := cmd.Output()
>
> Possible Swift:
>
> let proc = try Process.run(["ls", "-l"])
> let out = proc.stdout.read() // proc.stdout is OutputStream, assumes
> read() exists and returns Data
> // stderr available at proc.stderr
>
>
> 3) Run a command and capture both stdout and stder together
>
> Python:
> out = subprocess.check_output(["ls", "-l"], stderr=subprocess.STDOUT)
>
> Go:
> cmd := exec.Command("ls", "-l")
> out, err := cmd.CombinedOutput()
>
> Possible Swift:
> let proc = try Process.run(["ls", "-l"], combinedOutput: true)
> let out = proc.stdout.read()
>
>
> 4) Shell out
>
> Python:
> subprocess.check_output(["ls", "-l"], stderr=subprocess.STDOUT,
> shell=True)
>
> Go:
> cmd := exec.Command("sh", "-c", "ls -l")
> out, err := cmd.CombinedOutput()
>
> Possible Swift:
> let proc = try Process.run(["sh", "-c", "ls -l"], combinedOutput: true)
> let out = proc.stdout.read()
>
>
> 5) Pipe to stdin
>
> Python:
> p = subprocess.Popen(["wc"], stdin=subprocess.PIPE,
> stdout=subprocess.PIPE)
> p.stdin.write(b'blah')
> p.stdin.close()
> out = p.stdout.read()
>
> Go:
> cmd := exec.Command("wc")
> stdin, err := cmd.StdinPipe()
> io.WriteString(stdin, "blah")
> out = cmd.CombinedOutput()
>
> Possible Swift:
> let stdin = InputStream(data: "blah".data(using: .utf8))
> let proc = try Process.run(["wc"], stdin: stdin, combinedOutput: true)
> let out = proc.stdout.read()
>
> 6) Async
>
> Python:
> p = subprocess.Popen(["sleep", "5"])
> p.wait()
>
> Go:
> cmd := exec.Command("sleep", "5")
> err := cmd.Start()
> err2 := cmd.Wait()
>
> Possible Swift:
> let proc = Process(["sleep", "5"])
> try proc.start()
> try proc.wait()
>
>
> On Fri, Nov 17, 2017 at 9:34 PM, Tony Parker via swift-corelibs-dev
> <swift-corelibs-dev@swift.org <mailto:swift-corelibs-dev@swift.org>> wrote:
> Hi Abhi,
>
> It does seem like there is a possibility of some better convenience API here.
>
> Any ideas on what form it would take? A class method on Process that returns
> the output, maybe?
>
> - Tony
>
>> On Nov 16, 2017, at 3:34 PM, Abhi Beckert via swift-corelibs-dev
>> <swift-corelibs-dev@swift.org <mailto:swift-corelibs-dev@swift.org>> wrote:
>>
>> Swift is a great shell scripting language except for it's lack of any API to
>> execute UNIX commands. Compare these two shell scripts:
>>
>>> #!/usr/bin/php
>>> <?
>>>
>>> $files = `find ~/Desktop -name *.png`;
>>>
>>> foreach (explode("\n", $files) as $file) {
>>> // do something with $file
>>> }
>>
>> -
>>
>>> #!/usr/bin/swift
>>>
>>> import Foundation
>>>
>>> let process = Process()
>>> process.launchPath = "/usr/bin/find"
>>> process.arguments = [
>>> NSString(string:"~/Desktop").expandingTildeInPath,
>>> "-name",
>>> "*.png"
>>> ]
>>>
>>> let output = Pipe()
>>> process.standardOutput = output
>>>
>>> process.launch()
>>>
>>> let files: String
>>> if let filesUtf8 = NSString(data:
>>> output.fileHandleForReading.readDataToEndOfFile(), encoding:
>>> String.Encoding.utf8.rawValue) {
>>> files = filesUtf8 as String
>>> } else {
>>> files = NSString(data: output.fileHandleForReading.readDataToEndOfFile(),
>>> encoding: String.Encoding.isoLatin1.rawValue) as NSString! as String
>>> }
>>>
>>> files.enumerateLines { file, _ in
>>> // do something with file
>>> }
>>
>> It's a contrived example, I could have used NSFileManager, but I run into
>> this all the time integrating with more complex tools such as rsync.
>>
>> Adding my own high level wrapper around the Process command isn't an option
>> since there is no good way to import code from another file when executing
>> swift asa shell script. All your code needs to be in one file.
>>
>> - Abhi
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