Writing a chained command line tool

Where do I find example code, tutorial

There are not many users who write commandline tools in Swift, so it may be hard to find a good example or tutorial online.

But the concept of chainable commandline app is very simple, read input from standard input, write output to standard output.

(I assume you have a Mac with Xcode and its CommandLine Tools installed. If you have a question about Swift on other platform, you should better visit swit.org .)

Example:

double.swift

#!/usr/bin/swift
import Foundation

while let line = readLine() {
    print(line, line)
}

In Terminal:

OOPers-mini:commandline dev$ chmod +x double.swift

One thing bad for you is that Swift Standard Library does not have many functionalites to work with standard input and output.

You may need to use some C lib functions.

You can create a more complex CommandLine app, using Xcode or Swift package manager.

Is Swift a mandate? Because Python might be a better choice.

Thank you, it probably will solve my problem, but as far as I remember tool chaining requires a signaling mechanism, so not to flood the receiving tool.

When chaining inside swift, there is a Pipe and Process object that probably contains that.

Anyhow, my requirement this time is to augment a log file and the receiving tool won't have a problem processing the data fast enough.

Thank you.

as far as I remember tool chaining requires a signaling mechanism

my requirement this time is to augment a log file and the receiving tool won't have a problem processing the data fast enough.

Frankly, I do not understand what sort of functionality you are mentioning.

So, I recommend you to implement one simple functionaly of your own. And when you find some difficulty implementing what you want, you can start a new thread.

as far as I remember tool chaining requires a signaling mechanism, so not to flood the receiving tool.

I’m not sure what you’re getting at here.

readline

write

In theory you could construct your producer to do something clever in that case, but that assumes that you control the producer. From what you’ve posted it seems like you’re working on the consumer. If so, there’s really not much you can do other than to read data faster.

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