Writing in python may well be considered faster.

But as you say: Those utilities have already been implemented. In C. And they work beautifully. And they are fast - at least faster than they would be if implemented in Python. And they have far fewer dependencies: Remember that python is quite big, and probably not available on embedded systems.

Arguably, you could implement those utilities in any language, and use the same reasoning to argue they should be implemented in that language. How do you feel about C#? Ruby? C++? Haskell?

C was an excellent choice for writing those shell commands: it is low-level enough to produce very efficient small binaries, and high-level enough to implement the commands in a sensible way.

Re-implementing those commands in Python would yield you no benefits. Except that warm fuzzy feeling that “this is now Python!”. And your shell scripts would take more memory and run slower.

Oh: Don’t forget: Python is written in C ….

There are two ways this can happen.

The first is to redirect the output to a file, like this:

shell-script >output-file.txt 

This assumes that the shell script is executable.

The second method is if you want to write a shell script that writes a particular file or files. Normally, you don’t want to do that to capture all of the output because the flexibility of being able to redirect all of the output where you want it on each run is better. However, sometimes the point of a shell script is to create particular files. Also, sometimes you want to write to specific logs and so forth. You do that exactly the same way, except that you do it on individual commands within the script.

The simplest approach is to use the subprocess.check_output function:

>>> subprocess.check_output(['ls', '-l']) 

check_output runs a single program that takes only arguments as input

It returns the result exactly as printed to stdout. If you need to write input to stdin, skip ahead to the run or Popen sections. If you want to execute complex shell commands, see the note on shell=True at the end of this answer.

The check_output function works on almost all versions of Python still in wide use (2.7+). But for more recent versions, it is no longer the recommended approach.

Modern versions of Python (3.5 or higher): run

If you're using Python 3.5 or higher, and do not need backwards compatibility, the new run function is recommended. It provides a very general, high-level API for the subprocess module. To capture the output of a program, pass the subprocess.PIPE flag to the stdout keyword argument. Then access the stdout attribute of the returned CompletedProcess object:

>>> import subprocess 
>>> result = subprocess.run(['ls', '-l'], stdout=subprocess.PIPE) 
>>> result.stdout 

The return value is a bytes object, so if you want a proper string, you'll need to decode it. Assuming the called process returns a UTF-8-encoded string:

>>> result.stdout.decode('utf-8') 

This can all be compressed to a one-liner:

>>> subprocess.run(['ls', '-l'], stdout=subprocess.PIPE).stdout.decode('utf-8') 

If you want to pass input to the process's stdin, pass a bytes object to the input keyword argument:

>>> cmd = ['awk', 'length($0) > 5'] 
>>> input = 'foo\nfoofoo\n'.encode('utf-8') 
>>> result = subprocess.run(cmd, stdout=subprocess.PIPE, input=input) 
>>> result.stdout.decode('utf-8') 
'foofoo\n' 

You can capture errors by passing stderr=subprocess.PIPE (capture to result.stderr) or stderr=subprocess.STDOUT (capture to result.stdout along with regular output). When security is not a concern, you can also run more complex shell commands by passing shell=True as described in the notes below.

This adds just a bit of complexity, compared to the old way of doing things. But I think it's worth the payoff: now you can do almost anything you need to do with the run function alone.

Then write output where ever you like , in a way you want.

Usage

1. Save this script in a file (e.g., pythonrc.py).
2. Set the PYTHONSTARTUP environment variable to point to this file: export PYTHONSTARTUP=/path/to/pythonrc.py
3. Every time you open a Python interactive shell, these features will be enabled automatically.

This setup improves productivity by allowing quick recall of previous commands and intuitive tab-based auto-completion.

A shell script can be called from Python using built-in modules/methods.

For example - If we run echo command in windows cmd, we can display any string (works same as ‘print’ in most languages):

C:\Users\91797>echo "hello world!" 
"hello world!" 

Now, we can use the following methods to run the above command from Python.

Method 1: Using the os module:

>>> import os 
>>> os.system("echo 'hello world!'") 
'hello world!' 
0 

Method 2: Using the subprocess module:

>>> import subprocess 
>>> subprocess.run(["echo", "hello world!"], shell=True) 
"hello world!" 
CompletedProcess(args=['echo', 'hello world!'], returncode=0) 

I have Windows system, but the methods will work the same in Unix/Linux system also.

These are simple examples but both the modules can do much more complicated tasks. For more information, please refer to the Python official links for os module and subprocess module.

Hope this helps.

Happy Coding! 🙂

You are talking about command substitution. This has two forms: either the backquoted form:

myvar=`script.py` 

Or the braced form:

myvar=$(script.py) 

Note in both forms there should be no whitespace between myvar, =, and the substitution string.

This can be done to any executable command or script.

Now POSIX says that both forms are equal, except that in the backquoted form the back slash retains its meaning as an escape character when followed by \, “, ` (that is, back slash, double quote, and back quote). This is handy if you want to nest the back quotes, like having the output of one command embedded in the execution line of another command.

Another POSIX dictation is that if you double-quote either of the forms, then the shell will not perform those two steps on the command result:

• Pathname expansion
• Field splitting

That means if you are expecting multiple fields (or file names), e.g. output of ls, you should not surround the command substitution string in double quotes.

It’s unclear what you mean by “run a shell in Python.”

If you launch the Python interpreter with no arguments, then it comes up in an interactive “shell like” REPL environment. (REPL == Read, Evaluate, Print, Loop). This is a convenient way to play with Python, experiment with modules and with your own code, and learn how things work … what the documentation meant.

It’s also possible to embed such a “shell” (REPL) into your program as a feature or for debugging. This allows you to have your code run to some point, start your interactive “shell” for some time, then exit back into your code (which will execute from whatever state you left the process/session in).

Here’s how to do that: terminal.embed - IPython 7.13.0 documentation

(You don’t absolutely need to use Jupyter/IPython to get embedded Python functionality; but it’s the easiest way to do so, by far, and IPython is so tremendously useful beyond this that it’s hard to overstate).

You could also mean that you want to start an instance of your Unix command shell as a subprocess of your Python program. There are various ways of doing this as well, depending on whether you want to have your program able to feed commands to it, read responses back from it, and so on.

The simplest, and most limited, would be to simply import os and execute this function: os.system(os.environ[‘SHELL’]) … which will execute a shell and resume execute your Python code upon exit. Other options are in the subprocess module in Python’s standard libraries.

Use the Python DB-API driver for you database server. The sqlite3 DB-API interface is part of a standard Python build.

• sqlite3 - DB-API 2.0 interface for SQLite databases - Python 3.9.0 documentation

A database SELECT query returns a set of rows, not a single return value. Python sees this as a list of tuples returned by a generator.

A Python program must open a SELECT cursor object to make the generator. Then, read the tuples (rows) in a for-loop.

# Open a cursor object on the DB connection object. 
cur = conn.cursor() 
for row in cur.execute('SELECT * FROM stocks ORDER BY price'): 
	print(row) 
cur.close() 
# OUTPUT: 
('2006-01-05', 'BUY', 'RHAT', 100, 35.14) 
('2006-03-28', 'BUY', 'IBM', 1000, 45.0) 
('2006-04-06', 'SELL', 'IBM', 500, 53.0) 
('2006-04-05', 'BUY', 'MSFT', 1000, 72.0) 

Curl is a unix command which transfers data. It can send GET, POST, PUT and DELETE requests to URL.

Call requests.get(url) to send a GET request to the url.
Call request.post(url, data=dict) with url as a URL and dict as a dictionary of keys and values to send a POST request to url.
Call requests.put(url, data=dict) with url as a URL and dict as a dictionary of keys and values to send a PUT request to url.
Call requests.delete(url, data=dict) with url as URL and dict as a dictionary of keys and values to send a DELETE request to the url.
after sending a request, call requests.Response.status code to get the status of code of the get request or call requests.Response.text to get the text of the request.

url="https://google.com" 
res=requests.get(url) 
print(res.ststus_code) 

Output

200 

Python runs in its own python shell environment.
You may pass in external Environment variables via the os and sys modules, with some functions.

All environment variables created or changed inside a python environment are eliminated or revert to their previous values when the python interpreter exits.

Python and shells have stdin, stdout, and stderr in common, so you can simply print the value out to there and store in the enclosing script as the result of a call.

in sh or bash:

r="2.75"  # bash does not do floating point 
 
# python does 
 
pi=$(python -c 'import math; print((4 * math.atan(1)))') 
 
area=$(python -c "print((${pi} * ${r} ** 2))") 
 
echo "area of circle with radius ${r} = ${area}" 

area of circle with radius 2.75 = 23.7582944428

So python interprets the numerical strings as floats and bash interprets the results as strings.

The Python interactive shell is an interpreter for the Python programming language. The interactive nature means each statement is parsed and executed as it is typed. Python has a basic built-in capability, augmented by loading (importing) additional modules, some of which run commands using the system command shell, and others which implement complex functionality, such as creating graphical constructs or interactiing with database engines or client-server systems..

The command shell is an interactive interpreter for running scripts and compiled programs (such as the python shell) and system commands. The command interpreter or shell has its own internal language with syntactical constructs to implement loops and decision trees. Different systems have different command processors, each with their own syntax and built-in commands.

Windows has command.exe, macOS and Linux have Bash, with the option of using other variations on the Bourne Shell (the original Unix shell), or variations on the C shell, which was developed for BSD with similar syntax to the C programming language, but interactive.

Your question is basically the same as asking how French is different from English.