CODEWITHSUNDEEP
python-3.xsubprocess
droidian
droidian

Reputation: 89

Print output of ls -l | awk something

I want to get the output of command in a python script. The command is pretty straightforward - ls -l $filename | awk '{print $5}', essentially capture the size of a file

I have tried a couple of ways but I somehow can't get the variable filename passed in correctly.

What am I doing wrong with either approach?

Thanks for the help

Have tried two different ways as below:

Method 1

name = subprocess.check_output("ls -l filename | awk '{print $5}'", shell=True)
print name

Here ls complains that filename does not exist which I totally understand, but I am not sure what I would do to pass filename as a variable

Method 2

first = ['ls', '-l', filename]
second = ['awk', ' /^default/ {print $5}']
p1 = subprocess.Popen(first, stdout=subprocess.PIPE)
p2 = subprocess.Popen(second, stdin=p1.stdout, stdout=subprocess.PIPE)
out = p2.stdout.read()
print out

Here it just prints nothing.

actual result would be the size of the file.

Upvotes: 1

Views: 920

Answers (1)

Life is complex
Life is complex

Reputation: 15629

The builtin Python module os can provide you the size of a specific file.

Here is the documentation related to the methods below.

os.stat - reference

os.path.getsize - reference

Here are two methods using the Python module os to obtain the filesize:

import os

# Use os.stat with st_size
filesize_01 = os.stat('filename.txt').st_size
print (filesize_01)
# outputs 
30443963

# os.path.getsize(path) Return the size, in bytes, of path.
filesize_02 = os.path.getsize('filename.txt')
print (filesize_02)
# outputs 
30443963

I'm adding this subprocess example, because of the conversations concerning the use of os on this question. I decided to use the stat command over the ls command. I'm also using subprocess.check_output instead of subprocess.Popen, which was used in your question. The example below can be added to a try block with error handling.

subprocess.check_output - reference 

from subprocess import check_output

def get_file_size(filename):

   # stat command
   # -f display information using the specified format
   # the %z format selects the size in bytes
   output = check_output(['stat', '-f', '%z', str({}).format(filename)])

   # I also use the f-string in this print statement.
   # ref: https://realpython.com/python-f-strings/
   print(f"Filesize of {filename} is: {output.decode('ASCII')}")
   # outputs 
   30443963

get_file_size('filename.txt')

My personal preference is the os module, but yours might be the subprocess module.

Hopefully, one of these three methods will help solve your question.

Upvotes: 3

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