Watching something be piped to a file live with tail












2















I have a python program which is, slowly, generating some output.



I want to capture that in a file, but I also thought I could watch it live with tail.



So in one terminal I'm doing :



python myprog.py > output.txt


and in another terminal :



tail -f output.txt


But it seems like the tail isn't showing me anything while the python program is running. If I hit ctrl-c to kill the python script, suddenly the tail of output.txt starts filling up. But not while the python is running.



What am I doing wrong?






linux command-line pipe







share|improve this question


















  • 2





    How about python myprog.py | tee output.txt instead?

    – n8te
    2 hours ago
















2















I have a python program which is, slowly, generating some output.



I want to capture that in a file, but I also thought I could watch it live with tail.



So in one terminal I'm doing :



python myprog.py > output.txt


and in another terminal :



tail -f output.txt


But it seems like the tail isn't showing me anything while the python program is running. If I hit ctrl-c to kill the python script, suddenly the tail of output.txt starts filling up. But not while the python is running.



What am I doing wrong?






linux command-line pipe







share|improve this question


















  • 2





    How about python myprog.py | tee output.txt instead?

    – n8te
    2 hours ago














2












2








2








I have a python program which is, slowly, generating some output.



I want to capture that in a file, but I also thought I could watch it live with tail.



So in one terminal I'm doing :



python myprog.py > output.txt


and in another terminal :



tail -f output.txt


But it seems like the tail isn't showing me anything while the python program is running. If I hit ctrl-c to kill the python script, suddenly the tail of output.txt starts filling up. But not while the python is running.



What am I doing wrong?






linux command-line pipe







share|improve this question














I have a python program which is, slowly, generating some output.



I want to capture that in a file, but I also thought I could watch it live with tail.



So in one terminal I'm doing :



python myprog.py > output.txt


and in another terminal :



tail -f output.txt


But it seems like the tail isn't showing me anything while the python program is running. If I hit ctrl-c to kill the python script, suddenly the tail of output.txt starts filling up. But not while the python is running.



What am I doing wrong?






linux command-line pipe




linux command-line pipe






share|improve this question













share|improve this question











share|improve this question




share|improve this question










asked 2 hours ago









interstarinterstar

320310




320310








  • 2





    How about python myprog.py | tee output.txt instead?

    – n8te
    2 hours ago














  • 2





    How about python myprog.py | tee output.txt instead?

    – n8te
    2 hours ago








2




2





How about python myprog.py | tee output.txt instead?

– n8te
2 hours ago





How about python myprog.py | tee output.txt instead?

– n8te
2 hours ago










2 Answers
2






active

oldest

votes


















2














You may also need to explicitly flush the buffer for it to get piped upon generation. This is because output is typically only printed when the pipe's buffer fills up (which is in kilobytes I belive), and when the stdin message ends. This is probably to save on read/writes. You could do this after every print, or if you are looping, after the last print within the loop.



import sys
...
print('Some message')
sys.stdout.flush()






share|improve this answer








New contributor




Davey is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
Check out our Code of Conduct.




























    2














    Instead of trying to tail a live file, use tee instead. It was made to do exactly what you're trying to do.



    From man tee:




    tee(1) - Linux man page



    Name tee - read from standard input and write to standard output and files



    Synopsis



    tee [OPTION]... [FILE]...


    Description



    Copy standard input to each FILE, and also to standard output.



    -a, --append  
    
   append to the given FILEs, do not overwrite  
    
-i, --ignore-interrupts  
    
   ignore interrupt signals   
    
--help  
    
   display this help and exit  
    
--version
    
   output version information and exit


    If a FILE is -, copy again to standard output.




    So in your case you'd run:



    python myprog.py | tee output.txt





    share|improve this answer
























      Your Answer








      StackExchange.ready(function() {
      var channelOptions = {
      tags: "".split(" "),
      id: "3"
      };
      initTagRenderer("".split(" "), "".split(" "), channelOptions);

      StackExchange.using("externalEditor", function() {
      // Have to fire editor after snippets, if snippets enabled
      if (StackExchange.settings.snippets.snippetsEnabled) {
      StackExchange.using("snippets", function() {
      createEditor();
      });
      }
      else {
      createEditor();
      }
      });

      function createEditor() {
      StackExchange.prepareEditor({
      heartbeatType: 'answer',
      autoActivateHeartbeat: false,
      convertImagesToLinks: true,
      noModals: true,
      showLowRepImageUploadWarning: true,
      reputationToPostImages: 10,
      bindNavPrevention: true,
      postfix: "",
      imageUploader: {
      brandingHtml: "Powered by u003ca class="icon-imgur-white" href="https://imgur.com/"u003eu003c/au003e",
      contentPolicyHtml: "User contributions licensed under u003ca href="https://creativecommons.org/licenses/by-sa/3.0/"u003ecc by-sa 3.0 with attribution requiredu003c/au003e u003ca href="https://stackoverflow.com/legal/content-policy"u003e(content policy)u003c/au003e",
      allowUrls: true
      },
      onDemand: true,
      discardSelector: ".discard-answer"
      ,immediatelyShowMarkdownHelp:true
      });


      }
      });














      draft saved

      draft discarded


















      StackExchange.ready(
      function () {
      StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fsuperuser.com%2fquestions%2f1421123%2fwatching-something-be-piped-to-a-file-live-with-tail%23new-answer', 'question_page');
      }
      );

      Post as a guest















      Required, but never shown

























      2 Answers
      2






      active

      oldest

      votes








      2 Answers
      2






      active

      oldest

      votes









      active

      oldest

      votes






      active

      oldest

      votes









      2














      You may also need to explicitly flush the buffer for it to get piped upon generation. This is because output is typically only printed when the pipe's buffer fills up (which is in kilobytes I belive), and when the stdin message ends. This is probably to save on read/writes. You could do this after every print, or if you are looping, after the last print within the loop.



      import sys
      ...
      print('Some message')
      sys.stdout.flush()






      share|improve this answer








      New contributor




      Davey is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
      Check out our Code of Conduct.

























        2














        You may also need to explicitly flush the buffer for it to get piped upon generation. This is because output is typically only printed when the pipe's buffer fills up (which is in kilobytes I belive), and when the stdin message ends. This is probably to save on read/writes. You could do this after every print, or if you are looping, after the last print within the loop.



        import sys
        ...
        print('Some message')
        sys.stdout.flush()






        share|improve this answer








        New contributor




        Davey is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
        Check out our Code of Conduct.























          2












          2








          2







          You may also need to explicitly flush the buffer for it to get piped upon generation. This is because output is typically only printed when the pipe's buffer fills up (which is in kilobytes I belive), and when the stdin message ends. This is probably to save on read/writes. You could do this after every print, or if you are looping, after the last print within the loop.



          import sys
          ...
          print('Some message')
          sys.stdout.flush()






          share|improve this answer








          New contributor




          Davey is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
          Check out our Code of Conduct.










          You may also need to explicitly flush the buffer for it to get piped upon generation. This is because output is typically only printed when the pipe's buffer fills up (which is in kilobytes I belive), and when the stdin message ends. This is probably to save on read/writes. You could do this after every print, or if you are looping, after the last print within the loop.



          import sys
          ...
          print('Some message')
          sys.stdout.flush()







          share|improve this answer








          New contributor




          Davey is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
          Check out our Code of Conduct.









          share|improve this answer



          share|improve this answer






          New contributor




          Davey is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
          Check out our Code of Conduct.









          answered 2 hours ago









          DaveyDavey

          361




          361




          New contributor




          Davey is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
          Check out our Code of Conduct.





          New contributor





          Davey is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
          Check out our Code of Conduct.






          Davey is a new contributor to this site. Take care in asking for clarification, commenting, and answering.
          Check out our Code of Conduct.

























              2














              Instead of trying to tail a live file, use tee instead. It was made to do exactly what you're trying to do.



              From man tee:




              tee(1) - Linux man page



              Name tee - read from standard input and write to standard output and files



              Synopsis



              tee [OPTION]... [FILE]...


              Description



              Copy standard input to each FILE, and also to standard output.



              -a, --append  
              
   append to the given FILEs, do not overwrite  
              
-i, --ignore-interrupts  
              
   ignore interrupt signals   
              
--help  
              
   display this help and exit  
              
--version
              
   output version information and exit


              If a FILE is -, copy again to standard output.




              So in your case you'd run:



              python myprog.py | tee output.txt





              share|improve this answer




























                2














                Instead of trying to tail a live file, use tee instead. It was made to do exactly what you're trying to do.



                From man tee:




                tee(1) - Linux man page



                Name tee - read from standard input and write to standard output and files



                Synopsis



                tee [OPTION]... [FILE]...


                Description



                Copy standard input to each FILE, and also to standard output.



                -a, --append  
                
   append to the given FILEs, do not overwrite  
                
-i, --ignore-interrupts  
                
   ignore interrupt signals   
                
--help  
                
   display this help and exit  
                
--version
                
   output version information and exit


                If a FILE is -, copy again to standard output.




                So in your case you'd run:



                python myprog.py | tee output.txt





                share|improve this answer


























                  2












                  2








                  2







                  Instead of trying to tail a live file, use tee instead. It was made to do exactly what you're trying to do.



                  From man tee:




                  tee(1) - Linux man page



                  Name tee - read from standard input and write to standard output and files



                  Synopsis



                  tee [OPTION]... [FILE]...


                  Description



                  Copy standard input to each FILE, and also to standard output.



                  -a, --append  
                  
   append to the given FILEs, do not overwrite  
                  
-i, --ignore-interrupts  
                  
   ignore interrupt signals   
                  
--help  
                  
   display this help and exit  
                  
--version
                  
   output version information and exit


                  If a FILE is -, copy again to standard output.




                  So in your case you'd run:



                  python myprog.py | tee output.txt





                  share|improve this answer













                  Instead of trying to tail a live file, use tee instead. It was made to do exactly what you're trying to do.



                  From man tee:




                  tee(1) - Linux man page



                  Name tee - read from standard input and write to standard output and files



                  Synopsis



                  tee [OPTION]... [FILE]...


                  Description



                  Copy standard input to each FILE, and also to standard output.



                  -a, --append  
                  
   append to the given FILEs, do not overwrite  
                  
-i, --ignore-interrupts  
                  
   ignore interrupt signals   
                  
--help  
                  
   display this help and exit  
                  
--version
                  
   output version information and exit


                  If a FILE is -, copy again to standard output.




                  So in your case you'd run:



                  python myprog.py | tee output.txt






                  share|improve this answer












                  share|improve this answer



                  share|improve this answer










                  answered 2 hours ago









                  n8ten8te

                  5,16172234




                  5,16172234






























                      draft saved

                      draft discarded




















































                      Thanks for contributing an answer to Super User!


                      • Please be sure to answer the question. Provide details and share your research!

                      But avoid …



                      • Asking for help, clarification, or responding to other answers.

                      • Making statements based on opinion; back them up with references or personal experience.


                      To learn more, see our tips on writing great answers.




                      draft saved


                      draft discarded














                      StackExchange.ready(
                      function () {
                      StackExchange.openid.initPostLogin('.new-post-login', 'https%3a%2f%2fsuperuser.com%2fquestions%2f1421123%2fwatching-something-be-piped-to-a-file-live-with-tail%23new-answer', 'question_page');
                      }
                      );

                      Post as a guest















                      Required, but never shown





















































                      Required, but never shown














                      Required, but never shown












                      Required, but never shown







                      Required, but never shown

































                      Required, but never shown














                      Required, but never shown












                      Required, but never shown







                      Required, but never shown







                      -

                      Popular posts from this blog

                      What other Star Trek series did the main TNG cast show up in?

                      Image
                      .everyoneloves__top-leaderboard:empty,.everyoneloves__mid-leaderboard:empty,.everyoneloves__bot-mid-leaderboard:empty{ margin-bottom:0; } 4 I'm referring to Picard, Riker, Data, Worf, Geordi, Dr. Crusher, Wesley Crusher, Chief O'Brien and family, Deanna Troi, Guinan. I know Picard and Worf show up on DS9, though I haven't seen it myself. I'm curious what happened to the characters after that last episode of TNG? star-trek star-trek-tng share | improve this question edited 10 hours ago Ham Sandwich 6,051 2 25 75 ...
                      Read more

                      Berlina muro

                      Image
                      La berlina muro ĉe Bethaniendamm, 1986 La berlina muro aŭ simple la muro [1] , nomita ankaŭ "kontraŭfaŝisma remparo" en propaganda lingvo de la iama Germana Demokratia Respubliko, estis parto de la interngermana limo, kiu dividis de la 13-a de aŭgusto 1961 ĝis la 9-a de novembro 1989 okcidentan Berlinon de la orienta parto de la urbo kaj de la ĉirkaŭa tereno de la GDR. Ĝi estis unu el la plej famaj simboloj de la malvarma milito kaj de la disdivido de Germanio. Pli ol simpla muro, la berlina muro estis fakte tuta defendokonstruaĵo kun du muroj, ena malplena strio, rondirvojo, gardturoj kaj alarmsistemoj. Dum la provo transiri la severe garditan limon al okcidenta Berlino multaj homoj estis mortigitaj. La preciza nombro de viktimoj estas pridisputita kaj ne certa; la nombroj anoncataj varias inter 86 kaj 238 mortintoj. La malplifortiĝo de Sovetunio kaj la politiko de liberigo gvidita de Miĥail Gorbaĉov ebligis al la orientgermanoj faligi la 9-an de novembro 1989 l...
                      Read more

                      Berlina aerponto

                      Image
                      Flugkoridoroj dum la blokado de Berlino La Berlina aerponto estas la provizigo de okcidenta Berlino per aviadiloj fare de la aliancanoj inter la 23-a de junio 1948 kaj la 12-a de majo 1949 dum la blokado de Berlino fare de la sovetia armeo. Enhavo 1 Historio 1.1 La aerkoridoroj 1.2 Unuaj flugoj 1.3 Plibonigo de la aerponto 1.4 Fino de la aerponto 1.5 Rozinbombiloj 1.6 Bilanco 2 Flughavenoj 2.1 Berlino 2.2 Okcidenta Germanio 3 Aviadiloj de la berlina aerponto 4 15-a datreveno de la aerponto 5 Bibliografio 6 Referencoj 7 Eksteraj ligiloj Historio | General Lucius D. Clay, militguberniestro de la usona okupadzono Jam antaŭ la berlina aerponto estiĝis la malgranda aerponto . La estro de la sovetia militadministracio en Germanio, Vasili Daniloviĉ Sokolovski, ordonis la 1-an de aprilo 1948, kiel reago al la konferenco de Londono inter britoj, francoj kaj reprezentantoj de Benelukso pri aligo de Germa...
                      Read more