IPython notebook: using quotes(') and dollar($) to pass string variable as argument to python script in command-line(!) | eg: abc.py -arg1 '$var1'

Question

In using variables in the command line from a notebook cell, I saw that we can use put a $ in front of the variable, or surround the variable using {} , for example

!command {variable}

or

!command $variable

But when I was running a python script using the command line from a notebook cell, I would get errors

variable1 = '/path/to/directory'
variable2 = 7

!Script.py -arg1 $variable1 -arg2 $variable2

and

!Script.py -arg1 {variable1} -arg2 {variable2}

did not work.

After experimenting a little bit, I found that if a variable is a string, surrounding the whole arg with quotes got it to work.

variable1 = '/path/to/directory'
variable2 = 7

!Script.py -arg1 '$variable1' -arg2 $variable2 

What is going on? I tried to look up this phenomena but I couldn't find anything.

If it makes a difference, I am using google colab colaboratory

Answer 1

你有没有尝试过？

!Script.py -arg1 $variable1\ -arg2 $variable2\ 

Answer 2

Any input line beginning with a !character is passed verbatim(exclude the ! ) to the underlying command-line interface. [source]

Passing a string variable after ! character will pass only the string content, but not the ' (quotes) symbol. You need to surround the string variable with ' (quotes) symbol in your line.

---

Using your example above, the two variables:

variable1 = '/path/to/directory'
variable2 = 7

When running this line:

!Script.py -arg1 $variable1 -arg2 $variable2         #wrong

it will translate to

> Script.py -arg1 /path/to/directory -arg2 7

the quotation mark is not passed to the command-line.

---

So, you need to add the quotation mark around the string variable:

!Script.py -arg1 '$variable1' -arg2 $variable2       #correct

that will translate to

> Script.py -arg1 '/path/to/directory' -arg2 7

the quotation mark is passed to the command-line. The command will work properly and your observation is correct.