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@espadrine
Created September 12, 2014 11:32
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How to read stdin synchronously in nodejs.
var fs = require('fs');
// Returns a buffer of the exact size of the input.
// When endByte is read, stop reading from stdin.
function getStdin(endByte) {
var BUFSIZE = 256;
var buf = new Buffer(BUFSIZE);
var totalBuf = new Buffer(BUFSIZE);
var totalBytesRead = 0;
var bytesRead = 0;
var endByteRead = false;
var fd = process.stdin.fd;
// Linux and Mac cannot use process.stdin.fd (which isn't set up as sync).
var usingDevice = false;
try {
fd = fs.openSync('/dev/stdin', 'rs');
usingDevice = true;
} catch (e) {}
for (;;) {
try {
bytesRead = fs.readSync(fd, buf, 0, BUFSIZE, null);
// Copy the new bytes to totalBuf.
var tmpBuf = new Buffer(totalBytesRead + bytesRead);
totalBuf.copy(tmpBuf, 0, 0, totalBytesRead);
buf.copy(tmpBuf, totalBytesRead, 0, bytesRead);
totalBuf = tmpBuf;
totalBytesRead += bytesRead;
// Has the endByte been read?
for (var i = 0; i < bytesRead; i++) {
if (buf[i] === endByte) {
endByteRead = true;
break;
}
}
if (endByteRead) { break; }
} catch (e) {
if (e.code === 'EOF') { break; }
throw e;
}
if (bytesRead === 0) { break; }
}
if (usingDevice) { fs.closeSync(fd); }
return totalBuf;
}
var stdin = '';
function getline() {
if (stdin.length === 0) {
stdin = getStdin('\n'.charCodeAt(0)).toString('utf-8');
}
var newline = stdin.search('\n') + 1;
var line = stdin.slice(0, newline);
// Flush
stdin = stdin.slice(newline);
return line;
}
console.log('First line: "' + getline() + '"');
console.log('Second line: "' + getline() + '"');
@iONinja
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iONinja commented May 13, 2018

Does this work cross-platform? (i.e. Windows, Darwin and Linux)

@andy0130tw
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If you use "readFileSync" in Linux, it would be fine. However, reading process.stdin.fd first make it impossible to do that. Strange.

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