


In Bash scripts, if is suitable for simple logical judgment, and case is suitable for multi-value matching. 1. if is often used for dynamic condition judgments such as file existence and numerical comparison, and supports elif and else branch expansion; 2. case is more suitable for matching fixed values ??or patterns, such as classification processing of user input commands, supports wildcards and each branch must end with;; 3. Selection basis: use if for dynamic conditions, and case for fixed value matching.
In Bash scripts, if
and case
are two common ways to handle conditional judgments. They are each suitable for different scenarios: if
is more suitable for simple logical judgments, while case
is more suitable for matching multiple fixed values. Here are some practical uses and considerations.
Use if statements for conditional judgment
The if
statement in Bash is usually used with test expressions. The basic structure is as follows:
if [condition]; then # Execute command fi
You can also add else
or elif
to extend the logic:
if [ condition1 ]; then # Execute elif when condition 1 is true [ condition2 ]; then # Execute else when condition 2 is true # Execute fi when neither is true
Common usage examples:
Check if the file exists:
if [ -f "filename.txt" ]; then echo "File exists" else echo "File does not exist" fi
Compare numerical values:
if [ "$num" -gt 10 ]; then echo "The value is greater than 10" fi
Note: To compare strings, use =
, and to compare numeric values, use operators such as -eq
, -ne
, -lt
, -gt
.
Use case statements for multi-value matching
When multiple situations need to be matched based on the value of a variable, case
statement will be clearer and more concise. The syntax is as follows:
case $variable in pattern1) # Execute when pattern1 is matched;; pattern2) # Execute when pattern2 is matched;; *) #Default;; esac
Practical application scenarios:
For example, selecting an operation based on user input:
case $choice in start) echo "Start service" ;; stop) echo "stop service" ;; restart) echo "restart service" ;; *) echo "Invalid option" ;; esac
Features:
- Supports wildcards, such as
*.txt)
that can match all file names ending in.txt
. - Each branch must be added at the end
;;
to indicate the end, otherwise the execution of the next branch will continue (similar to C's switch).
How to choose between if and case?
These two statements are not substitutes for each other, but have their own applicable scenarios:
-
Using if:
- The conditions are dynamic, such as numerical comparison, file status, etc.
- Not many logical branches and simple structure
-
When using case:
- To match multiple fixed values ??or patterns
- The input source is user input or configuration items with limited and unambiguous values.
For example:
- If you are determining whether the user input is
yes
orno
, you can useif
- If you want to perform different operations based on the commands entered by the user (such as
start
,stop
,status
), it is clearer to usecase
That's basically it. Mastering the use of if
and case
can make your Bash script more flexible and easier to maintain.
The above is the detailed content of How to use conditional statements in bash if case. For more information, please follow other related articles on the PHP Chinese website!

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