execute python script with function from command line, Linux

This

if __name__ == "__main__":
    command= " ".join( sys.argv[1:] )
    eval( command )

This will work. But it's insanely dangerous.

You really need to think about what your command-line syntax is. And you need to think about why you're breaking the long-established Linux standards for specifying arguments to a program.

For example, you should consider removing the useless ()'s in your example. Make it this, instead.

python convertImage.py convertFile fileName

Then, you can -- with little work -- use argparse to get the command ("convertFile") and the arguments ("fileName") and work within the standard Linux command line syntax.

function_map = { 
    'convertFile': convertFile,
    'conv': convertFile,
}
parser = argparse.ArgumentParser()
parser.add_argument( 'command', nargs=1 )
parser.add_argument( 'fileName', nargs='+' )
args= parser.parse_args()
function = function_map[args.command]
function( args.fileName )

Quick and dirty way:

linux user$: python convertImage.py convertFile fileName

and then in convertImage.py

if __name__ == '__main__':
    import sys
    function = getattr(sys.modules[__name__], sys.argv[1])
    filename = sys.argv[2]
    function(filename)

A more sophisticated approach would use argparse (for 2.7 or 3.2+) or optparse.

Create a top-level executable part of your script that parses command-line argument(s) and then pass it to your function in a call, like so:

import os, sys
#import Image
import string


def convertFile(fileName):
    splitName = string.split(fileName, "_")
    endName = splitName[2]
    splitTwo = string.split(endName, ".")
    userFolder = splitTwo[0]

    imageFile = "/var/www/uploads/tmp/"+fileName

    print imageFile     # (rest of the script)

    return


if __name__ == '__main__':
    filename = sys.argv[1]
    convertFile(filename)

Then, from a shell,

$ convertImage.py the_image_file.png
/var/www/uploads/tmp/the_image_file.png