105 lines
2.5 KiB
JavaScript
105 lines
2.5 KiB
JavaScript
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var common = require('./common');
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var fs = require('fs');
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common.register('head', _head, {
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canReceivePipe: true,
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cmdOptions: {
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'n': 'numLines',
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},
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});
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// This reads n or more lines, or the entire file, whichever is less.
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function readSomeLines(file, numLines) {
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var BUF_LENGTH = 64 * 1024;
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var buf = new Buffer(BUF_LENGTH);
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var bytesRead = BUF_LENGTH;
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var pos = 0;
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var fdr = null;
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try {
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fdr = fs.openSync(file, 'r');
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} catch (e) {
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common.error('cannot read file: ' + file);
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}
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var numLinesRead = 0;
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var ret = '';
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while (bytesRead === BUF_LENGTH && numLinesRead < numLines) {
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bytesRead = fs.readSync(fdr, buf, 0, BUF_LENGTH, pos);
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var bufStr = buf.toString('utf8', 0, bytesRead);
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numLinesRead += bufStr.split('\n').length - 1;
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ret += bufStr;
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pos += bytesRead;
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}
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fs.closeSync(fdr);
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return ret;
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}
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//@
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//@ ### head([{'-n': \<num\>},] file [, file ...])
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//@ ### head([{'-n': \<num\>},] file_array)
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//@ Available options:
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//@
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//@ + `-n <num>`: Show the first `<num>` lines of the files
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//@
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//@ Examples:
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//@
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//@ ```javascript
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//@ var str = head({'-n': 1}, 'file*.txt');
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//@ var str = head('file1', 'file2');
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//@ var str = head(['file1', 'file2']); // same as above
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//@ ```
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//@
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//@ Read the start of a file.
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function _head(options, files) {
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var head = [];
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var pipe = common.readFromPipe();
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if (!files && !pipe) common.error('no paths given');
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var idx = 1;
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if (options.numLines === true) {
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idx = 2;
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options.numLines = Number(arguments[1]);
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} else if (options.numLines === false) {
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options.numLines = 10;
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}
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files = [].slice.call(arguments, idx);
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if (pipe) {
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files.unshift('-');
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}
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var shouldAppendNewline = false;
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files.forEach(function (file) {
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if (!fs.existsSync(file) && file !== '-') {
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common.error('no such file or directory: ' + file, { continue: true });
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return;
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}
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var contents;
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if (file === '-') {
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contents = pipe;
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} else if (options.numLines < 0) {
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contents = fs.readFileSync(file, 'utf8');
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} else {
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contents = readSomeLines(file, options.numLines);
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}
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var lines = contents.split('\n');
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var hasTrailingNewline = (lines[lines.length - 1] === '');
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if (hasTrailingNewline) {
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lines.pop();
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}
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shouldAppendNewline = (hasTrailingNewline || options.numLines < lines.length);
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head = head.concat(lines.slice(0, options.numLines));
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});
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if (shouldAppendNewline) {
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head.push(''); // to add a trailing newline once we join
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}
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return head.join('\n');
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}
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module.exports = _head;
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