I'm looking for the best way to use bash commands from within python. What ways are there? I know of os.system and subprocess.Popen.
I have tried these:
bootfile = os.system("ls -l /jffs2/a.bin | cut -d '/' -f 4")
print bootfile
This returns a.bin as expected but also it retuns 0 afterwards and so prints:
a.bin
0
with bootfile now being set to 0. The next time I print bootfile it just shows up as 0. Which is the exit value I guess, how do i stop this value interfering?
I have also tried:
bootfile = subprocess.Popen("ls -l /jffs2/a.bin | cut -d '/' -f 4")
print bootfile
but it seems to break the script, as in I get nothing returned at all, have I done that right?
Also which of these is better and why? Are there other ways and what is the preferred way?
Using os.readlink (proposed by #kojiro) and os.path.basename for getting only the namefile:
os.path.basename(os.readlink('/jffs2/a.bin'))
kojiro's comment about os.readlink is probably what you want.
I am explaining what you were trying to implement.
os.system would return you exit status of the command run.
subprocess.Popen will create a pipe, so that you can capture the output of the command run.
Below line will capture output of the command run:
bootfile = subprocess.Popen(["bash","-c","ls -l /jffs2/a.bin | cut -d '/' -f 4"], stdout=subprocess.PIPE).communicate()[0]
More details at http://docs.python.org/library/subprocess.html
The right answer, as #kojiro says, is:
os.readlink('/jffs2/a.bin')
But if you really wanted to do this the complicated way, then in Python 2.7:
cmd = "ls -l /jffs2/a.bin | cut -d '/' -f 4"
bootfile = subprocess.check_output(cmd, shell=True)
Or on older Pythons:
cmd = "ls -l /jffs2/a.bin | cut -d '/' -f 4"
p = subprocess.Popen(cmd, shell=True, stdout=subprocess.PIPE)
bootfile = p.communicate()[0]
if p.returncode != 0:
raise Exception('It failed')
Related
I am trying to assign to a variable the fingerprint of a pgp key in a bash subprocess of a python script.
Here's a snippet:
import subprocess
subprocess.run(
'''
export KEYFINGERPRINT="$(gpg --with-colons --fingerprint --list-secret-keys | sed -n 's/^fpr:::::::::\([[:alnum:]]\+\):/\1/p')"
echo "KEY FINGERPRINT IS: ${KEYFINGERPRINT}"
''',
shell=True, check=True,
executable='/bin/bash')
The code runs but echo shows an empty variable:
KEY FINGERPRINT IS:
and if I try to use that variable for other commands I get the following error:
gpg: key "" not found: Not found
HOWEVER, if I run the same exact two lines of bash code in a bash script, everything works perfectly, and the variable is correctly assigned.
What is my python script missing?
Thank you all in advance.
The problem is the backslashes in your sed command. When you paste those into a Python string, python is escaping the backslashes. To fix this, simply add an r in front of your string to make it a raw string:
import subprocess
subprocess.run(
r'''
export KEYFINGERPRINT="$(gpg --with-colons --fingerprint --list-secret-keys | sed -n 's/^fpr:::::::::\([[:alnum:]]\+\):/\1/p')"
echo "KEY FINGERPRINT IS: ${KEYFINGERPRINT}"
''',
shell=True, check=True,
executable='/bin/bash')
in order to run 2 commands in subprocess you need to run them one after each other or use ;
import subprocess
ret = subprocess.run('export KEYFINGERPRINT="$(gpg --with-colons --fingerprint --list-secret-keys | sed -n 's/^fpr:::::::::\([[:alnum:]]\+\):/\1/p')"; echo "KEY FINGERPRINT IS: ${KEYFINGERPRINT}"', capture_output=True, shell=True)
print(ret.stdout.decode())
you can use popen:
commands = '''
export KEYFINGERPRINT="$(gpg --with-colons --fingerprint --list-secret-keys | sed -n 's/^fpr:::::::::\([[:alnum:]]\+\):/\1/p')"
echo "KEY FINGERPRINT IS: ${KEYFINGERPRINT}"
'''
process = subprocess.Popen('/bin/bash', stdin=subprocess.PIPE, stdout=subprocess.PIPE)
out, err = process.communicate(commands)
print out
I'm having a problem with my subprocess command, I like to grep out the lines that match with "Online" line.
def run_command(command):
p = subprocess.Popen(command,shell=False,
stdout=subprocess.PIPE,
stderr=subprocess.STDOUT)
return iter(p.stdout.readline, b'')
command = 'mosquitto_sub -u example -P example -t ITT/# -v | grep "Online" '.split()
for line in run_command(command):
print(line)
But I will get an error
Error: Unknown option '|'.
Use 'mosquitto_sub --help' to see usage.
But when running with linux shell
user#server64:~/Pythoniscriptid$ mosquitto_sub -u example -P example -t ITT/# -v | grep "Online"
ITT/C5/link Online
ITT/IoT/tester55/link Online
ITT/ESP32/TEST/link Online
I also tried shell = True, but with no success, because I will get another error, that dosen't recognize the topic ITT/#
Error: You must specify a topic to subscribe to.
Use 'mosquitto_sub --help' to see usage.
The "possible dublicate" didn't help me at all, So I think I'm having a different problem. I tried to change code to this, put in not getting any return
def run_command(command,command2):
p1 = subprocess.Popen(command,stdout=subprocess.PIPE,stderr=subprocess.STDOUT)
p2 = subprocess.Popen(command2,stdin=p1.stdout,stdout=subprocess.PIPE)
return iter(p2.stdout.readline,'')
command = 'mosquitto_sub -u example -P example -t ITT/# -v'.split()
command2 = 'grep Online'.split()
#subprocess.getoutput(command)
for line in run_command(command,command2):
print(line)
When you split the text, the list will look like
['mosquitto_sub', ..., 'ITT/#', '-v', '|', 'grep', '"Online"']
When you pass this list to subprocess.Popen, a literal '|' will be one of the arguments to mosquitto_sub.
If you use shell=True, you must escape any special characters like # in the command, for instance with double quotes:
import subprocess
command = 'echo -e "ITT/#\\ni am Online\\nbar Online\\nbaz" | grep "Online" '
p = subprocess.Popen(
command, shell=True, stdout=subprocess.PIPE, stderr=subprocess.STDOUT)
for line in iter(p.stdout.readline, b''):
print(line)
Alternatively, connect the pipes as you wrote, but make sure to iterate until b'', not u'':
import subprocess
def run_command(command, command2):
p1 = subprocess.Popen(command,stdout=subprocess.PIPE,stderr=subprocess.STDOUT)
p2 = subprocess.Popen(command2,stdin=p1.stdout,stdout=subprocess.PIPE)
return iter(p2.stdout.readline, b'')
command = ['echo', '-e', 'ITT/#\\ni am Online\\nbar Online\\nbaz']
command2 = 'grep Online'.split()
for line in run_command(command,command2):
print(line)
The line awk -F'[][]' '/dB/ { print $2 }' <(amixer sget Master) in bash returns my system's current volume (e.g. "97%").
I tried to incorporate this in Python 3
#!/usr/bin/env python3
import subprocess
command = "awk -F'[][]' '/dB/ { print $2 }' <(amixer sget Master)"
output = subprocess.Popen(command, shell=True, stdout=subprocess.PIPE).stdout.read()
print(output)
However the output from the shell returns
/bin/sh: 1: Syntax error: "(" unexpected
b''
Why does this fail and how do I fix my code?
As already pointed out, the syntax you are using is a bash syntax (a.k.a. bashism). The default shell used in subprocess.Popen is /bin/sh & it does not support process substitution.
You can specify the shell to be used via executable argument.
Try this:
output = subprocess.Popen(command, shell=True, stdout=subprocess.PIPE, executable="/bin/bash").stdout.read()
Because you are using bashism in form of a process substitution, and your /bin/sh doesn't support that:
<(...)
Changing this to a pipe should solve your problem:
command = "amixer sget Master | awk -F'[][]' '/dB/ { print $2 }'"
Alternative you can start bash from within sh:
command = "bash -c 'amixer sget Master | awk -F'\\''[][]'\\'' '\\''/dB/ { print $2 }'\\'''"
But as you will soon realize, quoting and escaping will become a nightmare
How do I place output of bash command to Python variable?
I am writing a Python script, which I want to enter the output of
bash command:
rpm -qa --qf '%{NAME}-%{VERSION}-%{RELEASE}.%{ARCH} %{VENDOR}\n' | grep -v 'Red Hat'|wc -l, and place it to Python variable, let say R.
After that I want to do, Python if R != 0
then run some Linux command.
How do I achieve that?
There are various options, but the easiest is probably using subprocess.check_output() with shell=True although this can be security hazard if you don't fully control what command is passed in.
import subprocess
var = subprocess.check_output('rpm -qa --qf '%{NAME}-%{VERSION}-%{RELEASE}.%{ARCH} %{VENDOR}\n' | grep -v 'Red Hat'|wc -l', shell = True)
var = int(var)
You need to use shell=True as otherwise the pipes would not be interpreted.
If you need more control you might want to look at plumbum where you can do:
from plumbum.cmd import rpm, grep, wc
chain = rpm["-qa", "--qf", r"%{NAME}-%{VERSION}-%{RELEASE}.%{ARCH} %{VENDOR}\n"] | grep["-v", "Red Hat"] | wc["-l"]
R = int(chain())
Although I would probably not invoke wc and get the whole output and count its length within python (easier to check that you got just the lines that you expected, piping through wc -l throws away all of the details)
I would recommend envoy primarily because the API is much more intuitive to use for 90% of the use cases.
r = envoy.run('ls ', data='data to pipe in', timeout=2)
print r.status_code # returns status code
print r.std_out # returns the output.
See the Envoy Github page for more details.
You can use stdin.
#!/usr/bin/python
import sys
s = sys.stdin.read()
print s
Then you will run a bash command like this
echo "Hello" | ./myscript.py
Output
Hello
You can replace shell pipeline using Popen:
from subprocess import PIPE,Popen
p1 = Popen(["rpm", "-qa", "--qf", '%{NAME}-%{VERSION}-%{RELEASE}.%{ARCH} %{VENDOR}\n'],stdout=PIPE)
p2 = Popen(["grep", "-v", 'Red Hat'],stdin=p1.stdout,stdout=PIPE)
p1.stdout.close()
p3 = Popen(["wc", "-l"],stdin=p2.stdout,stdout=PIPE)
p2.stdout.close()
out,err = p3.communicate()
If you just want to check if grep returned any matches then forget the wc - l and just check what grep returns:
p1 = Popen(["rpm", "-qa", "--qf", '%{NAME}-%{VERSION}-%{RELEASE}.%{ARCH} %{VENDOR}\n'],stdout=PIPE)
p2 = Popen(["grep", "-v", 'Red Hat'],stdin=p1.stdout,stdout=PIPE)
p1.stdout.close()
out,err = p2.communicate()
if out:
...
Or just use check_output to run the rpm command and check the string for "Red Hat":
out = check_output(["rpm", "-qa", "--qf", '%{NAME}-%{VERSION}-%{RELEASE}.%{ARCH} %{VENDOR}\n'])
if "Red Hat" not in out:
....
Which is the same as inverting the search with grep -v then checking if there are any matches with wc.
I'm trying to grep a list of file from the "*.nasl" of "Openvas" which contains a certain port's number.
I can make it directly in the terminal with the command :
egrep --only-match '111' /home/gwvm/Openvas/var/lib/openvas/plugins/*.nasl |cut -d ":" -f1
This command return all the name of the nasl file which contains 111.
like :
/home/gwvm/Openvas/var/lib/openvas/plugins/SolarWinds_TFTP.nasl:111
/home/gwvm/Openvas/var/lib/openvas/plugins/trojan_horses.nasl:111
and after the cut :
/home/gwvm/Openvas/var/lib/openvas/plugins/SolarWinds_TFTP.nasl
/home/gwvm/Openvas/var/lib/openvas/plugins/trojan_horses.nasl
But when I'm in python(3.1.3) the output give me an error :
egrep:/home/gwvm/Openvas/var/lib/openvas/plugins/*.nasl: No such file or directory
i was thinking about a problem because of the "*.nasl" but when I'm trying with an existing file, same result.
Here is the part of code :
command = ("egrep --only-match '"+ str(port[0]) +"' "+ openvas_directory["locate"]["nasl"] + '*.nasl' + ' |cut -d ":" -f1 ')
process=sp.Popen(command,shell=True, stdout= sp.PIPE)
or
exec(command)
I was thinking too of a bad construction but wen I'm printing the command it gives me what i want :
egrep --only-match '111' /home/gwvm/Openvas/var/lib/openvas/plugins/*.nasl |cut -d ":" -f1
If there are any idea!
from subprocess import PIPE, Popen
x = Popen('egrep --only-match \'111\' /home/gwvm/Openvas/var/lib/openvas/plugins/*.nasl', stdout=PIPE, stderr=PIPE, shell=True)
y = Popen('cut -d ":" -f1', stdin=x.stdout, stdout=PIPE, stderr=PIPE, shell=True)
for row in y.stdout.readline():
print row
Or just use check_output()
And this is btw how you | in Popen ;)
Guidelines:
When using Popen, if you supply a command as a string, use shell=True.
If you however supply Popen with a list ['ls, '-l'] then use shell=False, that's just how it works.
If you're piping data, execute two different Popen's and use the output from the first command as stdin for the second command, this is equivilant to doing | in Linux.