How to pass parameter to python script from Unix

Question

I have been researching over the internet

like How to pass parameter to inside python code which is embedded within Unix function

Overview :

function_name()
{

python -c << END 
...... python code .....
...... python code .....
...... python code .....
END 

}

Below is the way I call above Unix function into my main.sh script and execute it

. /d/demo/function.sh

echo "Function started"
function_name 10 5 
echo "Function ended"

If parameter passed to function was a digit[number] , then I was successful in passing parameter to python script like below and got expected output : 15

function_name()
{
    get_value1="$1"
    get_value2="$2" python -c << END 
    import os 
    firstparameter=int(os.environ['getvalue1'])
    secondparameter=int(os.environ['getvalue2'])
    C=firstparameter + secondparameter
    print (C)
    END 
}

But if i want to pass string like path ='/d/demo/ABC' , How to do ?

concatenate_ABC()
{
    a="$1"
    b="$2" 
    c="$3"
    python -c << END

    import os 
    get_path=int(os.environ['a'])
    get_filename=int(os.environ['b'])
    get_nm=int(os.environ['c'])

    with open (get_path+'/'+get_filename,r) as f:
                 
        fname=get_path +'/' + get_nm 
        print (fname) 
    END 
}

Below is the way I call above Unix function into my main.sh script and trying to execute not able to achieve

. /d/demo/function.sh

echo "Function started"
concatenate_ABC "/d/demo/ABC" "Dummy.txt" "XYZ"
echo "Function ended"

The Dummy.txt file as list of path name

/d/d1
/d/d2
/d/d3
/d/d4

So from function the parameter should be passed to python code like below

concatenate_ABC "/d/demo/ABC" "Dummy.txt" "XYZ"

The above 3 parameters should be used in code like below

    get_path="/d/demo/ABC"
    get_filename=Dummy.txt
    get_nm=XYZ

with open (get_path + '/' + get_filename,r) as f:
    fname=get_path +'/' + get_nm 
    print (fname)

Maybe see tutorialspoint.com/python/python_command_line_arguments.htm or realpython.com/python-command-line-arguments/#the-sysargv-array . I don't know if it is possible to combine command line arguments with feeding the Python script into python's standard input. That's why it would be better to write the Python code as separate Python scripts as suggested by Raspberry PyCharm — Bodo
– Bodo, Commented Jun 16, 2021 at 12:47
@Bodo I got your point but I want it without creating extra script file that is the reason i embedded into only one script within a Unix function itself , if you see it works for this function_name() where i am passing function_name() 10 5 it should be working for string also — codeholic24
– codeholic24, Commented Jun 16, 2021 at 12:51
Then try something like python "$script" "arg1" "arg2" ..., see stackoverflow.com/a/32239857/10622916 and the other answers . — Bodo
– Bodo, Commented Jun 16, 2021 at 12:59
Not a very clean way, but you also could create templates of your scripts to populate with arguments later, using envsubst (see this answer). — Lenormju
– Lenormju, Commented Jun 17, 2021 at 16:41

haridsv · Accepted Answer · 2021-06-20 12:15:09Z

OP's approach will work, but casting to int while accessing environment variable is wrong since these are strings. However, there are many other types and issues:

OP is not exporting the environment variables, so they won't be accessible from the script.
The open call has a typo, the second argument should be 'r' instead of `r'.
The END of here document can't be indented.

Some of the above problems also exist with OP's first example that apparently worked, but I don't see anyway it could have.

Here is a function that works (note that the content inside here document is indented with a hard tab character). Also, OP is opening the file but not doing anything with the contents, so I added a loop showing its use (needed for my own test):

concatenate_ABC()
{
    read -r -d '' script <<-"----END"
    import os
    get_path=os.environ['a']
    get_filename=os.environ['b']
    get_nm=os.environ['c']
    
    with open(get_path+'/'+get_filename, 'r') as f:
        for line in f:
            fname=get_path +'/' +line.strip()+'/'+ get_nm 
            print(fname) 
----END
    export a="$1"
    export b="$2" 
    export c="$3"
    python -c "$script"
}

Considering one can also pass arguments to python -c, we don't actually need to make use of environment variables (again watch for tab chars):

concatenate_ABC()
{
    read -r -d '' script <<-"----END"
    import sys
    get_path = sys.argv[1]
    get_filename = sys.argv[2]
    get_nm = sys.argv[3]
    
    with open(get_path+'/'+get_filename, 'r') as f:
        for line in f:
            fname=get_path +'/' +line.strip()+'/'+ get_nm 
            print(fname) 
----END
    python -c "$script" $*
}

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