如何在 Node.js 中使用流处理文件

1mkdir node-file-streams

1cd node-file-streams

1nano mycliprogram

1[label node-file-streams/mycliprogram]
2#!/usr/bin/env node
3
4const args = process.argv;
5const commands = ['read', 'write', 'copy', 'reverse'];

 1[label node-file-streams/mycliprogram]
 2...
 3const getHelpText = function() {
 4    const helpText = `
 5    simplecli is a simple cli program to demonstrate how to handle files using streams.
 6    usage:
 7        mycliprogram <command> <path_to_file>
 8
 9        <command> can be:
10        read: Print a file's contents to the terminal
11        write: Write a message from the terminal to a file
12        copy: Create a copy of a file in the current directory
13        reverse: Reverse the content of a file and save its output to another file.
14
15        <path_to_file> is the path to the file you want to work with.
16    `;
17    console.log(helpText);
18}

 1[label node-file-streams/mycliprogram]
 2...
 3let command = '';
 4
 5if(args.length < 3) {
 6    getHelpText();
 7    return;
 8}
 9else if(args.length > 4) {
10    console.log('More arguments provided than expected');
11    getHelpText();
12    return;
13}
14else {
15    command = args[2]
16    if(!args[3]) {
17        console.log('This tool requires at least one path to a file');
18        getHelpText();
19        return;
20    }
21}

1./mycliprogram

1[secondary_label Output]
2-bash: ./mycliprogram: Permission denied

1chmod +x mycliprogram

1[secondary_label Output]
2simplecli is a simple cli program to demonstrate how to handle files using streams.
3usage:
4    mycliprogram <command> <path_to_file>
5
6    read: Print a file's contents to the terminal
7    write: Write a message from the terminal to a file
8    copy: Create a copy of a file in the current directory
9    reverse: Reverse the content of a file and save it output to another file.

 1[label node-file-streams/mycliprogram]
 2...
 3switch(commands.indexOf(command)) {
 4    case 0:
 5        console.log('command is read');
 6        break;
 7    case 1:
 8        console.log('command is write');
 9        break;
10    case 2:
11        console.log('command is copy');
12        break;
13    case 3:
14        console.log('command is reverse');
15        break;
16    default:
17        console.log('You entered a wrong command. See help text below for supported functions');
18        getHelpText();
19        return;
20}

1./mycliprogram read test.txt

1[secondary_label Output]
2command is read

1wget https://raw.githubusercontent.com/do-community/node-file-streams/999e66a11cd04bc59843a9c129da759c1c515faf/lorem-ipsum.txt

1[label node-file-streams/mycliprogram]
2#!/usr/bin/env node
3
4const fs = require('fs');

 1[label node-file-streams/mycliprogram]
 2...
 3function read(filePath) {
 4    const readableStream = fs.createReadStream(filePath);
 5
 6    readableStream.on('error', function (error) {
 7        console.log(`error: ${error.message}`);
 8    })
 9
10    readableStream.on('data', (chunk) => {
11        console.log(chunk);
12    })
13}

1[label node-file-streams/mycliprogram]
2...
3switch (command){
4    case 0:
5        read(args[3]);
6        break;
7    ...
8}

1./mycliprogram read lorem-ipsum.txt

1[secondary_label Output]
2<Buffer 0a 0a 4c 6f 72 65 6d 20 69 70 73 75 6d 20 64 6f 6c 6f 72 20 73 69 74 20 61 6d 65 74 2c 20 63 6f 6e 73 65 63 74 65 74 75 72 20 61 64 69 70 69 73 63 69 ... >
3...
4<Buffer 76 69 74 61 65 20 61 6e 74 65 20 66 61 63 69 6c 69 73 69 73 20 6d 61 78 69 6d 75 73 20 75 74 20 69 64 20 73 61 70 69 65 6e 2e 20 50 65 6c 6c 65 6e 74 ... >

1[label node-file-streams/mycliprogram]
2
3...
4const readableStream = fs.createReadStream(filePath, 'utf8')
5...

1[secondary_label Output]
2Lorem ipsum dolor sit amet, consectetur adipiscing elit. Aenean est tortor, eleifend et enim vitae, mattis condimentum elit. In dictum ex turpis, ac rutrum libero tempus sed...
3
4...
5
6...Quisque nisi diam, viverra vel aliquam nec, aliquet ut nisi. Nullam convallis dictum nisi quis hendrerit. Maecenas venenatis lorem id faucibus venenatis. Suspendisse sodales, tortor ut condimentum fringilla, turpis erat venenatis justo, lobortis egestas massa massa sed magna. Phasellus in enim vel ante viverra ultricies.

1[label node-file-streams/mycliprogram]
2#!/usr/bin/env node
3
4const fs = require('fs');
5const readline = require('readline');

1[label node-file-streams/mycliprogram]
2...
3function write(filePath) {
4    const writableStream = fs.createWriteStream(filePath);
5
6    writableStream.on('error',  (error) => {
7        console.log(`An error occured while writing to the file. Error: ${error.message}`);
8    });
9}

 1[label node-file-streams/mycliprogram]
 2...
 3function write(filePath) {
 4    const writableStream = fs.createWriteStream(filePath);
 5
 6    writableStream.on('error',  (error) => {
 7        console.log(`An error occured while writing to the file. Error: ${error.message}`);
 8    });
 9
10    const rl = readline.createInterface({
11        input: process.stdin,
12        output: process.stdout,
13        prompt: 'Enter a sentence: '
14    });
15
16    rl.prompt();
17
18    rl.on('line', (line) => {
19        switch (line.trim()) {
20            case 'exit':
21                rl.close();
22                break;
23            default:
24                sentence = line + '\n'
25                writableStream.write(sentence);
26                rl.prompt();
27                break;
28        }
29    }).on('close', () => {
30        writableStream.end();
31        writableStream.on('finish', () => {
32            console.log(`All your sentences have been written to ${filePath}`);
33        })
34        setTimeout(() => {
35            process.exit(0);
36        }, 100);
37    });
38}

 1[label node-file-streams/mycliprogram]
 2...
 3switch (command){
 4    ...
 5
 6    case 1:
 7        write(args[3]);
 8        break;
 9
10    ...
11}

1./mycliprogram write output.txt

1[secondary_label Output]
2Enter a sentence: Twinkle, twinkle, little star
3Enter a sentence: How I wonder what you are
4Enter a sentence: Up above the hills so high
5Enter a sentence: Like a diamond in the sky
6Enter a sentence: exit
7All your sentences have been written to output.txt

1./mycliprogram read output.txt

1[secondary_label Output]
2Twinkle, twinkle, little star
3How I wonder what you are
4Up above the hills so high
5Like a diamond in the sky

 1[label example.js]
 2const fs = require('fs');
 3const readableStream = fs.createReadStream('lorem-ipsum.txt', 'utf8');
 4const writableStream = fs.createWriteStream('lorem-ipsum-copy.txt');
 5
 6readableStream.on('data', () => {
 7    writableStream.write(chunk);
 8});
 9
10writableStream.end();

 1[label node-file-streams/mycliprogram]
 2...
 3function copy(filePath) {
 4    const inputStream = fs.createReadStream(filePath)
 5    const fileCopyPath = filePath.split('.')[0] + '-copy.' + filePath.split('.')[1]
 6    const outputStream = fs.createWriteStream(fileCopyPath)
 7
 8    inputStream.pipe(outputStream)
 9
10    outputStream.on('finish', () => {
11        console.log(`You have successfully created a ${filePath} copy. The new file name is ${fileCopyPath}.`);
12    })
13}

 1[label node-file-streams/mycliprogram]
 2...
 3switch (command){
 4    ...
 5
 6    case 2:
 7        copy(args[3]);
 8        break;
 9
10    ...
11}

1./mycliprogram copy lorem-ipsum.txt

1[secondary_label Output]
2You have successfully created a lorem-ipsum-copy.txt copy. The new file name is lorem-ipsum-copy.txt.

1[label mycliprogram]
2#!/usr/bin/env node
3...
4const stream = require('stream');
5const Transform = stream.Transform || require('readable-stream').Transform;

 1[label node-file-streams/mycliprogram]
 2...
 3function reverse(filePath) {
 4    const readStream = fs.createReadStream(filePath);
 5    const reversedDataFilePath = filePath.split('.')[0] + '-reversed.'+ filePath.split('.')[1];
 6    const writeStream = fs.createWriteStream(reversedDataFilePath);
 7
 8    const reverseStream = new Transform({
 9        transform (data, encoding, callback) {
10            const reversedData = data.toString().split("").reverse().join("");
11            this.push(reversedData);
12            callback();
13        }
14    });
15
16    readStream.pipe(reverseStream).pipe(writeStream).on('finish', () => {
17        console.log(`Finished reversing the contents of ${filePath} and saving the output to ${reversedDataFilePath}.`);
18    });
19}

 1[label node-file-streams/mycliprogram]
 2...
 3switch (command){
 4    ...
 5
 6    case 3:
 7        reverse(args[3]);
 8        break;
 9
10    ...
11}

1wget https://raw.githubusercontent.com/do-community/node-file-streams/999e66a11cd04bc59843a9c129da759c1c515faf/countries.csv

1./mycliprogram reverse countries.csv

1[secondary_label Output]
2Finished reversing the contents of countries.csv and saving the output to countries-reversed.csv.