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This article mainly introduces "how to use the double parentheses of shell". In the daily operation, I believe many people have doubts about how to use the double parentheses of shell. The editor consulted all kinds of materials and sorted out simple and easy-to-use methods of operation. I hope it will be helpful to answer the doubts of "how to use double parentheses of shell". Next, please follow the editor to study!

Usage: syntax: (expression 1, expression 2. )) Features: 1, in the double parenthesis structure, all expressions can be the same as c language, such as: axioms, expressions, etc. 2. In the double parenthesis structure, all variables can not be prefixed with the "$" symbol. 3. Double parentheses can be used for logical operations. 4. Double parentheses structure extends for,while,if conditional test operation 5. Multiple expression operations are supported. Each expression is used separately. Examples of separate use: expansion of four operations #! / bin/sha=1;b=2;c=3; ((a=a+1)); echo $a * ((axi1m * baud @)). Echo $a _ r _ r running result:] # sh testsh.sh23,3,4 supports multiple expressions between double parenthesis structures, and then supports common c language operators such as addition, subtraction, multiplication and division. If the double parentheses are marked with: $, you will get the expression value and assign it to the left variable. Extended logic operation #! / bin/sha=1;b= "ab"; echo $((a > 1mm 8echo 9)); ((aecho = "a")) & echo "err2"; ((aecho "ok"; run result:] # sh testsh.sh9err2ok extended flow control statement (logical relationship) #! / bin/shnum=100;total=0;for ((iLife0 total+=i); doneecho $total;total=0;i=0;while ((iTun5050)); then echo "ok") Result of fi operation:] # sh testsh.sh50505050ok

With the double parenthesis operators: [[]], [], test logic operations, let,expr can be thrown aside.

At this point, the study on "how to use the double parentheses of shell" is over. I hope to be able to solve your doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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