Python subprocess.popen上的标准输出不一致

Question

I'm trying to execute below system command using python :

cat txt_file | egrep "keyword1|keyword2|keyword3"

using below python code :

p1 = subprocess.Popen (['cat', txt_file], stdout=subprocess.PIPE)
p2 = subprocess.Popen (['egrep', "\"" + keyword_list + "\""], stdin=p1.stdout, stdout=subprocess.PIPE)

#where keyword_list is : "keyword1|keyword2|keyword3"

p1.stdout.close() #for p2 to exit if SIGPIPE from p1
out = p2.communicate()[0]

There are multiple lines for the egrep output, But using the above script I'm able to get only the line matching the middle keyword2 in the variable out .

What might be the issue here?

Update : Platform : windows txt_file is quite big ~8 MB

Answer 1

I suppose it is the "\\"" stuff (which would look nicer as '"' , BTW).

You are calling Popen() without shell=True , so you should give the parameters as you want them. On a normal egrep call the "" are stripped away by the shell, a step which you don't have here. SO you don't need them here.

Answer 2

Issue resolved by the following workaround:

#Using file as stdin for p2
txt_file = open ('txt_file_path')
p2 = subprocess.Popen (['egrep', keyword_list, stdin=txt_file)
out = p2.communicate()[0]
txt_file.close()