1. String Qiatouquwei #,%
For example:
X=aabbaarealwwvvww
echo "${x%w*w}"
Aabbaarealwwvv
echo "${x%%w*w}"
Aabbaareal
echo "${x# #a *a}"
Lwwvvww
echo "${x#a*a}"
Bbaarealwwvvww
Where, # means pinch the head, because on the keyboard # on the left.
Where,% is said to go to the tail, because on the keyboard% on the right.
A single represents the minimum match, and the two represent the maximum match. That is, when there are multiple scenarios for matching, select the maximum length or minimum length to match.
2. If else syntax simple description
if [condition]
Then ...//conditions for the establishment of the implementation
Else
...//When the condition is not established
3. DirName command
Removes the suffix of the file path. Useful when getting a configuration directory folder.
Example: dirname/usr/bin/test.txt result is/usr/bin
Shell syntax and tips-Continuous updates