Since you mention python, a python answer:
if you simply want to set a default value for an argument, you can simply set the default for the function:
def show(val = 30):
print(val)
# to print the default value (30)
show()
# to show another value (e.g. 40)
show(40)
In other words, this will print the default value if you give no argument, while it uses the argument if you give it.
More advanced; reading the default values from a file, with the option to overrule by giving the arguments
The very same can be done, but reading default arguments from a file. This will give the opportunity to set arguments in a settings file instead of editing them in the code itself.
Let's say I have a settings file, testconf.txt:
length:4
height:7
width:6
...and I want to read these values into my application as default arguments, but the user can overrule them by custom arguments:
#!/usr/bin/env python3
import sys
# path to my config file
conf_file = "/home/jacob/Bureaublad/testconf.txt"
# read the default arguments from a file
def_args = [l.strip() for l in open(conf_file).readlines()]
# replace default args by possible custom args
cust_args = sys.argv[1:]
for cu in cust_args:
argname = cu.split(":")[0]
try:
match = [arg for arg in def_args if arg.startswith(argname)][0]
except IndexError:
print("incorrect argument: ", cu)
else:
def_args[def_args.index(match)] = cu
def get_arg(s):
return [val.split(":")[1] for val in def_args if val.startswith(s)][0]
l = get_arg("length")
w = get_arg("width")
h = get_arg("height")
print("l=", l, "w=", w, "h=", h)
Now I can run the script without arguments:
$ '/home/jacob/Bureaublad/pscript_4.py'
l= 4 w= 6 h= 7
Or width arguments:
$ '/home/jacob/Bureaublad/pscript_4.py' length:10 height:456
l= 10 w= 6 h= 456
The order of given arguments is in this setup irrelevant. In case of an incorrect argument:
$ '/home/jacob/Bureaublad/pscript_4.py' monkey
incorrect argument: monkey
l= 4 w= 6 h= 7
Note
In "real" software, you can (and should) make it more advanced of course by adding a warning if the settings file is incorrect or missing, decide what to do then, but this is the basic idea.
EDIT
From your comments, I understand that in two ways, the above answer is not (yet) what you are looking for:
- You'd like to run the command without the path to the executable (script), and its extension, and
- You'd like to have a more "conventional" format of the options.
Although [1] is anwered elsewhere already, I'll include a brief explanation here:
1. Run the command without path and extension
You can run executables and scripts without having to include the path to the script by making it executable (chmod +x <files>), and place them anywhere in $PATH.
On Linux, the extension (.py) does not play a role whatsoever, so you can use the script without extension anyway.
To be concrete:
- create, if it doesn't exist yet, the directory
~/bin
create and save the script, exactly as mentioned in the original answer, as showsize (no extenion) in ~/bin, and make the script executable.
After a log out/in, you can simply run the script by the command:
showsize
2. Change the format of the options
As mentioned, you can change the format of the options easily, e.g.: To parse out the options, given like:
-l 23 -h 210 -w 321
If you include in the script:
args = sys.argv[1:]
The result for argswill be a list:
["-l", "23", "-h", "210", "-w", "321"]
Now what we need to do to get the value of -h, is simply look up the index of -h, and pick the first next item in the list:
height = args[args.index("-h")+1]
print(height)
> 210
in a script:
#!/usr/bin/env python3
import sys
# path to my config file
conf_file = "/home/jacob/Bureaublad/testconf.txt"
# read the default arguments from a file
def_args = [l.strip().split(":") for l in open(conf_file).readlines()]
# replace default args by possible custom args
cust_args = sys.argv[1:]
for carg in cust_args:
if carg in ["-l", "-h", "-w"]:
for d in def_args:
d[1] = cust_args[cust_args.index(carg)+1] if d[0] == carg else d[1]
def get_arg(s):
# fetch values from the list
return [val[1] for val in def_args if val[0] == s][0]
l = get_arg("-l")
w = get_arg("-w")
h = get_arg("-h")
print("length =", l, "\nwidth =", w, "\nheight =", h)
How to use
Create your settings file in the format:
-l:4
-h:7
-w:6
Copy the script into an empty file, svae it as showsize (no extension) in ~/bin or anywhere else in $PATH, and make it executable.
In the head section of the script, set the path to the settings file:
# path to my config file
conf_file = "/home/jacob/Bureaublad/testconf.txt"
Now run the command:
$ showsize
length = 4
width = 6
height = 7
Or:
$ showsize -l 300 -h 345 -w 751
length = 300
width = 751
height = 345
