sys.stdout.write does not grep

Question

I have a python script that writes to a screen as a startup script. I want to monitor the progress of the server so I go into a loop checking the status. I don't want to write down the screen. Therefore I'm using sys.stdout.write. The issue is that the program I'm using (wlst Weblogic) prints all this logging which I don't want to display. I get around this by using grep and only printing lines that start with a space.

I have this function

def printRoll():
   print ' Is my Print working'
   myTest = ' Hello'
   myTest1 = 'test 123'
   sys.stdout.write("\r %s " % myTest)
   sys.stdout.flush()
   systime.sleep(10)
   sys.stdout.write("\r  %s " % myTest1)
   sys.stdout.flush()
   systime.sleep(10)

What I want to display is:

 Is my Print working
 Hello

then after 10 seconds Hello is over written with

 test 123

if I run the grep command

python 'printRoll()' | grep '^[[:space:]]\{1\}[A-Za-z0-9]' --line-buffered 

it only prints the first line

Is my Print working

It wont print any of the sys.stdout.write lines. I think it is an issue with the buffering but I can't find an example for my issue.

The python script works as expected but it also includes lots of other info I don't want to print to screen.

Any help appreciated.

I believe it is an old version of Python, ie 2.7

cheers James

Answer 1

The thing is the other lines aren't new lines as far as grep is concerned, as you are not outputting a \\n newline character.

What grep sees is – this output is via xxd for a hex dump so we can see all the characters – the following. 0a (on the second line in the dump) is the newline character. You can see that there are no more newline characters ( 0a s) after that, so there's nothing more for grep to slice the input to lines on.

00000000: 2049 7320 6d79 2050 7269 6e74 2077 6f72   Is my Print wor
00000010: 6b69 6e67 0a0d 2020 4865 6c6c 6f20 0d20  king..  Hello . 
00000020: 2074 6573 7420 3132 3320                  test 123