expr Command

The expr command is used in Unix and Unix-like operating systems, including Linux, to evaluate expressions and return the result. expr can be used to perform arithmetic operations, comparisons, and string operations.

Perform arithmetic operations:

expr 5 + 2
expr 10 - 3
expr 3 \* 4
expr 20 / 5

Perform comparisons:

expr 5 \> 2
expr 5 \< 2
expr 5 \== 5

Perform string operations:

expr "hello" : '.*\(...\)'
expr length "hello"

Use expr to extract substrings:

expr "hello" : '\(...\)'

Use expr to calculate the length of a string:

expr length "hello"

Combine arithmetic and string operations

expr substr "hello" 2 3

Use expr in shell scripts

result=$(expr $a + $b)

expr command is quite powerful for evaluating simple expressions and is particularly useful for shell script. However it does not have floating point support, also it does not handle spaces very well in expressions so it can be a bit tricky to use in more complex scenarios. In most cases, it’s better to use a programming language such as bash, python or ruby to perform more complex operations.

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Other Linux Commands

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