Shell syntax and tips-Continuous updates

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