Develop Reference

Execute chained bash commands including multiple pipes and grep in Python3

I have to use the below bash command in a python script which includes multiple pip and grep commands.
grep name | cut -d':' -f2 | tr -d '"'| tr -d ','
I tried to do the same using subprocess module but didn't succeed.
Can anyone help me to run the above command in Python3 scripts?
I have to get the below output from a file file.txt.
Tom
Jack
file.txt contains:
"name": "Tom",
"Age": 10
"name": "Jack",
"Age": 15
Actually I want to know how can run the below bash command using Python.
cat file.txt | grep name | cut -d':' -f2 | tr -d '"'| tr -d ','

This works without having to use the subprocess library or any other os cmd related library, only Python.
my_file = open("./file.txt")
line = True
while line:
line = my_file.readline()
line_array = line.split()
try:
if line_array[0] == '"name":':
print(line_array[1].replace('"', '').replace(',', ''))
except IndexError:
pass
my_file.close()

If you not trying to parse a json file or any other structured file for which using a parser would be the best approach, just change your command into:
grep -oP '(?<="name":[[:blank:]]").*(?=",)' file.txt
You do not need any pipe at all.
This will give you the output:
Tom
Jack
Explanations:
-P activate perl regex for lookahead/lookbehind
-o just output the matching string not the whole line
Regex used: (?<="name":[[:blank:]]").*(?=",)
(?<="name":[[:blank:]]") Positive lookbehind: to force the constraint "name": followed by a blank char and then another double quote " the name followed by a double quote " extracted via (?=",) positive lookahead
demo: https://regex101.com/r/JvLCkO/1

Store filtered output of cmd command in a variable

I am trying to store the output of a cmd command as a variable in python.
To achieve this i am using os.system() but os.system() just runs the process,it doesn't capture the output.
import os
PlatformName = os.system("adb shell getprop | grep -e 'bt.name'")
DeviceName = os.system("adb shell getprop | grep -e '.product.brand'")
DeviceID = os.system("adb shell getprop | grep -e 'serialno'")
Version = os.system("adb shell getprop | grep -e 'version.release'")
print(PlatformName)
print(DeviceName)
print(DeviceID)
print(Version)
Then i tried to use the subprocess module.
import subprocess
import os
PlatformName = subprocess.check_output(["adb shell getprop | grep -e 'bt.name'"])
DeviceName = subprocess.check_output(["adb shell getprop | grep -e '.product.brand'"])
DeviceID = subprocess.check_output(["adb shell getprop | grep -e 'serialno'"])
Version = subprocess.check_output(["adb shell getprop | grep -e 'version.release'"])
print(PlatformName)
print(DeviceName)
print(DeviceID)
print(Version)
I am getting the following error
FileNotFoundError: [WinError 2] The system cannot find the file
specified
How can I store the output of the command as a variable?

The issues here:
passing arguments like this (string in a list, with spaces) is really not recommended
passing arguments like this need shell=True for it to have a slight chance to work, and shell=True is known for security issues (and other issues as well, like non-portability)
grep is not standard on windows, and the pattern is a regex which means you'd probably have to escape . ("bt\.name").
when not found grep returns 1 and would make check_output fail.
when found grep returns match(es), and a newline, that you'd have to strip
I'd rewrite this:
PlatformName = subprocess.check_output(["adb shell getprop | grep -e 'bt.name'"])
as:
output = subprocess.check_output(["adb","shell","getprop"])
platform_name = next((line for line in output.decode().splitlines() if "bt.name" in line),"")
The second line is a "native" version of grep (without regexes). It returns the first occurrence of "bt.line" in the output lines or empty string if not found.
You don't need grep here (the above is not strictly equivalent, as it yields the first occurrence, not all the occurrences but that should be okay on your case). And your clients may not have grep installed on Windows.

Hey I got the same problem as you. Sub-process can do what you want even with the shell=False. The trick is the communicate() method.
with subprocess.Popen(cmdCode,
stdin=subprocess.PIPE,
stdout=subprocess.PIPE,
stderr=subprocess.PIPE,
cwd = workingDir,
bufsize=1,
universal_newlines = True) as proc:
#output is stored in proc.stdout
#errors are stored in proc.stderr
Now you just need a little function to scan the proc.stdout for the information you need: PlatformName, etc

run linux grep command from python subprocess

I know there are posts already on how to use subprocess in python to run linux commands but I just cant get the syntax correct for this one. please help. This is the command I need to run...
/sbin/ifconfig eth1 | grep "inet addr" | awk -F: '{print $2}' | awk '{print $1}'
Ok this is what I have at the moment that gives a syntax error...
import subprocess
self.ip = subprocess.Popen([/sbin/ifconfig eth1 | grep "inet addr" | awk -F: '{print $2}' | awk '{print $1}'])
Any help greatly appreciated.

This has been gone over many, many times before; but here is a simple pure Python replacement for the inefficient postprocessing.
from subprocess import Popen, PIPE
eth1 = subprocess.Popen(['/sbin/ifconfig', 'eth1'], stdout=PIPE)
out, err = eth1.communicate()
for line in out.split('\n'):
line = line.lstrip()
if line.startswith('inet addr:'):
ip = line.split()[1][5:]

Here's how to construct the pipe in Python (rather than reverting to Shell=True, which is more difficult to secure).
from subprocess import PIPE, Popen
# Do `which` to get correct paths
GREP_PATH = '/usr/bin/grep'
IFCONFIG_PATH = '/usr/bin/ifconfig'
AWK_PATH = '/usr/bin/awk'
awk2 = Popen([AWK_PATH, '{print $1}'], stdin=PIPE)
awk1 = Popen([AWK_PATH, '-F:', '{print $2}'], stdin=PIPE, stdout=awk2.stdin)
grep = Popen([GREP_PATH, 'inet addr'], stdin=PIPE, stdout=awk1.stdin)
ifconfig = Popen([IFCONFIG_PATH, 'eth1'], stdout=grep.stdin)
procs = [ifconfig, grep, awk1, awk2]
for proc in procs:
print(proc)
proc.wait()
It'd be better to do the string processing in Python using re. Do this to get the stdout of ifconfig.
from subprocess import check_output
stdout = check_output(['/usr/bin/ifconfig', 'eth1'])
print(stdout)

How to run awk -F\' '{print $2}' inside subprocess.Popen in Python?

I need to run a shell command inside subprocess.Popen in Python.
The command is:
$ virsh dumpxml server1 | grep 'source file' | awk -F\' '{print $2}'
The output is:
/vms/onion.qcow2
I'm having two challenges with the above command:
1) The command is inside a loop, and where you see 'server1', it is a variable that will have a server name.
2) Python is complaining about KeyError: 'print $2'
Here is what I have so far:
proc = subprocess.Popen(["virsh dumpxml {0} | grep 'source file' | awk -F\' '{print $2}'".format(vm)], stdout=subprocess.PIPE, shell=True)
stdout = proc.communicate()[0]
Thanks in advance.

While it's possible use libvirt directly from python, your problem is that { is the format string, and surrounds print $2 in your awk script as well, so you have to escape those braces like
proc = subprocess.Popen(["virsh dumpxml {0} | grep 'source file' | awk -F\\' '{{print $2}}'".format(vm)], stdout=subprocess.PIPE, shell=True)
stdout = proc.communicate()[0]

Fabric, retrieving result of a bash command into a python variable

I would like to store the result of a command in a variable.
By instance running : a = sudo("ls -l my_filename | awk '{print $11}'")
How could I achieve this ?

a = sudo("ls -l my_filename | awk '{print $11}'", capture=True )