Ji Geng 44 / 90

Random thoughts on programming

Bash loop

while

while condition; do
  commands
done

until

until Circulation and while The cycle is just the opposite , As long as it doesn't meet the judgment criteria （ Conditions fail to judge ）, And then we cycle through the specified statement . Once the judgment conditions are met , Just exit the loop .

until condition; do
  commands
done

for...in

for variable in list
do
  commands
done

for

for (( expression1; expression2; expression3 )); do
  commands
done
// In the above code ,expression1 Used to initialize loop conditions ,expression2 The condition used to determine the end of the loop ,expression3 Execute at the end of each iteration of the loop , Used to update values .

select

select name
[in list]
do
  commands
done

Bash  Would be right select Do the following in turn .
1.select Create a menu , The content is a list list Each of , And each item is preceded by a number .
2.Bash  Prompt the user to select an item , Enter its number .
3. After user input ,Bash  The content of this item will be stored in a variable name, The item number is stored in the environment variable REPLY. If the user doesn't type , Just press enter ,Bash  Will re output the menu , Let users choose .
4. Executive command body commands.
5. After execution , Back to step one , Repeat the process .

eg:
select brand in Samsung Sony iphone symphony Walton
do
  echo "You have chosen $brand"
done

$ ./select.sh
1) Samsung
2) Sony
3) iphone
4) symphony
5) Walton
#?

Python if sentence

if condition:
  ...
elif condition:
  ...
else:
  ...