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
























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      2 Answers
      2






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      oldest

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      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






























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