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var common = require('./common');
var fs = require('fs');
common.register('head', _head, {
canReceivePipe: true,
cmdOptions: {
'n': 'numLines',
},
});
// This reads n or more lines, or the entire file, whichever is less.
function readSomeLines(file, numLines) {
var buf = common.buffer();
var bufLength = buf.length;
var bytesRead = bufLength;
var pos = 0;
var fdr = null;
try {
fdr = fs.openSync(file, 'r');
} catch (e) {
common.error('cannot read file: ' + file);
}
var numLinesRead = 0;
var ret = '';
while (bytesRead === bufLength && numLinesRead < numLines) {
bytesRead = fs.readSync(fdr, buf, 0, bufLength, pos);
var bufStr = buf.toString('utf8', 0, bytesRead);
numLinesRead += bufStr.split('\n').length - 1;
ret += bufStr;
pos += bytesRead;
}
fs.closeSync(fdr);
return ret;
}
//@
//@ ### head([{'-n': \<num\>},] file [, file ...])
//@ ### head([{'-n': \<num\>},] file_array)
//@ Available options:
//@
//@ + `-n <num>`: Show the first `<num>` lines of the files
//@
//@ Examples:
//@
//@ ```javascript
//@ var str = head({'-n': 1}, 'file*.txt');
//@ var str = head('file1', 'file2');
//@ var str = head(['file1', 'file2']); // same as above
//@ ```
//@
//@ Read the start of a file.
function _head(options, files) {
var head = [];
var pipe = common.readFromPipe();
if (!files && !pipe) common.error('no paths given');
var idx = 1;
if (options.numLines === true) {
idx = 2;
options.numLines = Number(arguments[1]);
} else if (options.numLines === false) {
options.numLines = 10;
}
files = [].slice.call(arguments, idx);
if (pipe) {
files.unshift('-');
}
var shouldAppendNewline = false;
files.forEach(function (file) {
if (file !== '-') {
if (!fs.existsSync(file)) {
common.error('no such file or directory: ' + file, { continue: true });
return;
} else if (fs.statSync(file).isDirectory()) {
common.error("error reading '" + file + "': Is a directory", {
continue: true,
});
return;
}
}
var contents;
if (file === '-') {
contents = pipe;
} else if (options.numLines < 0) {
contents = fs.readFileSync(file, 'utf8');
} else {
contents = readSomeLines(file, options.numLines);
}
var lines = contents.split('\n');
var hasTrailingNewline = (lines[lines.length - 1] === '');
if (hasTrailingNewline) {
lines.pop();
}
shouldAppendNewline = (hasTrailingNewline || options.numLines < lines.length);
head = head.concat(lines.slice(0, options.numLines));
});
if (shouldAppendNewline) {
head.push(''); // to add a trailing newline once we join
}
return head.join('\n');
}
module.exports = _head;
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