redirect - The order of stdout and stderr in bash - 


ls test.mp4  test.sh 1>/tmp/text  2>&1 cat   /tmp/text ls: cannot access test.sh: no such file or directory test.mp4

why result not following order?

test.mp4 ls: cannot access test.sh: no such file or directory

maybe 1>/tmp/text executed first, , test.mp4 locate before test.sh.
result in effect?

this has nothing bash. reflects way c standard library i/o functions buffer output.

here's useful excerpt man setvbuf on linux system (the explanation derived c , posix standards, think it's easy find , understand in excerpt). second paragraph explanation behaviour see.

the 3 types of buffering available unbuffered, block buffered, , line buffered. when output stream unbuffered, information appears on destination file or terminal written; when block buffered many characters saved , written block; when line buffered characters saved until newline output or input read stream attached terminal device (typically stdin). function fflush(3) may used force block out early. (see fclose(3).)

normally files block buffered. if stream refers terminal (as stdout does), line buffered. standard error stream stderr unbuffered default.

so, recap. stdout refers terminal , therefore line-buffered, have redirected file block buffered. however, stderr unbuffered whether or not has been redirected.

consequently, printed stderr appears immediately, while printed stdout held until buffer fills (on linux, 8kb).

note when ls detects stdout not terminal, sets -1 flag default (one filename per line). otherwise, set -x flag default (as many filenames fit on line). means see same inversion on terminal without redirecting @ all:

$ ls bad ls: cannot access bad: no such file or directory

Comments

Post a Comment

Popular posts from this blog

node.js - Node js - Trying to send POST request, but it is not loading javascript content -

i have been trying send post request website, , has not been loading full site. i guessing problem node js not loading javascript content, executing it. can see javascript in response, though never loads content javascript files producing in html. what mean is, doesn't execute javascript. how make node js code overcome this, , wait the full website load? have tried native code, , "request' module, both producing same errors. if helps, don't need native javascript. modules fine. some code have tried (request module): var options = { method: 'post', uri: 'https://url', formdata: { 'email': 'email', 'prize': '0', 'transactional': 'on' }, headers: { /* 'content-type': 'application/x-www-form-urlencoded' */ // set automatically } }; rp(options) .then(function (body) { console.log(body) }) .catch(function (err) { console.log(err) }); when fetch content...
Read more

javascript - Replicate keyboard event with html button -

i have tried few ways make happen. have javascript pinball game uses keyboard keys controls. converting application touch screen display. workaround, hoping overlay buttons when clicked simulate keyboard strokes. have done research , sounds should work. using jquery v3.2.1 here things have tried far... html element: <input type="button" class="coil"></input> $('.coil').trigger({type: 'keydown', which: 40, keycode: 40}); with this, not errors, nothing happens. var coilkey = $('body').keydown(function(e) { switch (e.keycode) { case 40: break;} }) $('.coil').click(coilkey); this 1 returns error in console... ((jquery.event.special[handleobj.origtype] || (intermediate value)).handle || handleobj.handler).apply not function below javascript game engine handles key listeners... addkeylistener: function (keyandlistener) { this.keylisteners.push(keyandlistener); }, // gi...
Read more

javascript - Web audio api 5.1 surround example not working in firefox -

i've been playing lott lately web audio api on both firefox , chrome. few days ago started experiment surround set. when trying surround audio in web audio api came notice example works fine in chrome v59 not in firefox v54. // create web audio api context var audioctx = new (window.audiocontext || window.webkitaudiocontext)(); audioctx.destination.channelinterpretation = 'discrete'; audioctx.destination.channelcountmode = 'explicit'; audioctx.destination.channelcount = 6; var oscillators = []; var merger = audioctx.createchannelmerger(6); console.log(audioctx.destination, merger); //merger.channelinterpretation = 'discrete'; //merger.channelcountmode = 'explicit'; //merger.channelcount = 6; var addoscilator = function(channel, frequency) { var oscillator = audioctx.createoscillator(); oscillator.frequency.value = frequency; // value in hertz oscillator.connect(merger,0,channel); oscillator.start(); oscillators.push(o...
Read more