This snippet on the Advanced Bash Scripting Guide says:
# The == comparison operator behaves differently within a double-brackets
# test than within single brackets.
[[ $a == z* ]] # True if $a starts with a "z" (wildcard matching).
[[ $a == "z*" ]] # True if $a is equal to z* (literal matching).
So you had it nearly correct; you needed double brackets, not single brackets.
With regards to your second question, you can write it this way:
HOST=user1
if [[ $HOST == user1 ]] || [[ $HOST == node* ]] ;
then
echo yes1
fi
HOST=node001
if [[ $HOST == user1 ]] || [[ $HOST == node* ]] ;
then
echo yes2
fi
Which will echo
yes1
yes2
Bash's if
syntax is hard to get used to (IMO).
Answer in one line:
''.join(random.choice(string.ascii_uppercase + string.digits) for _ in range(N))
or even shorter starting with Python 3.6 using random.choices()
:
''.join(random.choices(string.ascii_uppercase + string.digits, k=N))
A cryptographically more secure version: see this post
''.join(random.SystemRandom().choice(string.ascii_uppercase + string.digits) for _ in range(N))
In details, with a clean function for further reuse:
>>> import string
>>> import random
>>> def id_generator(size=6, chars=string.ascii_uppercase + string.digits):
... return ''.join(random.choice(chars) for _ in range(size))
...
>>> id_generator()
'G5G74W'
>>> id_generator(3, "6793YUIO")
'Y3U'
How does it work ?
We import string
, a module that contains sequences of common ASCII characters, and random
, a module that deals with random generation.
string.ascii_uppercase + string.digits
just concatenates the list of characters representing uppercase ASCII chars and digits:
>>> string.ascii_uppercase
'ABCDEFGHIJKLMNOPQRSTUVWXYZ'
>>> string.digits
'0123456789'
>>> string.ascii_uppercase + string.digits
'ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789'
Then we use a list comprehension to create a list of 'n' elements:
>>> range(4) # range create a list of 'n' numbers
[0, 1, 2, 3]
>>> ['elem' for _ in range(4)] # we use range to create 4 times 'elem'
['elem', 'elem', 'elem', 'elem']
In the example above, we use [
to create the list, but we don't in the id_generator
function so Python doesn't create the list in memory, but generates the elements on the fly, one by one (more about this here).
Instead of asking to create 'n' times the string elem
, we will ask Python to create 'n' times a random character, picked from a sequence of characters:
>>> random.choice("abcde")
'a'
>>> random.choice("abcde")
'd'
>>> random.choice("abcde")
'b'
Therefore random.choice(chars) for _ in range(size)
really is creating a sequence of size
characters. Characters that are randomly picked from chars
:
>>> [random.choice('abcde') for _ in range(3)]
['a', 'b', 'b']
>>> [random.choice('abcde') for _ in range(3)]
['e', 'b', 'e']
>>> [random.choice('abcde') for _ in range(3)]
['d', 'a', 'c']
Then we just join them with an empty string so the sequence becomes a string:
>>> ''.join(['a', 'b', 'b'])
'abb'
>>> [random.choice('abcde') for _ in range(3)]
['d', 'c', 'b']
>>> ''.join(random.choice('abcde') for _ in range(3))
'dac'
Best Answer
Heredoc sounds more convenient for this purpose. It is used to send multiple commands to a command interpreter program like ex or cat
The string after
<<
indicates where to stop.To send these lines to a file, use:
You could also store these lines to a variable:
This stores the lines to the variable named
VAR
.When printing, remember the quotes around the variable otherwise you won't see the newline characters.
Even better, you can use indentation to make it stand out more in your code. This time just add a
-
after<<
to stop the tabs from appearing.But then you must use tabs, not spaces, for indentation in your code.