Shell Script Raiders (learning notes)--1.5 to perform mathematical operations

Use Let, (()), or [] for basic integer operations, using expr and BC for advanced operations, including decimal operations.

[Email protected] tmp]# str= [[email protected] tmp]# let str=str+6[email protected] tmp]# let str-=5echo $str

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You can also self-increment, subtract from the operation.

[[email protected] tmp]# let str++; Echo $str

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[[email protected] tmp]# let ++str; Echo

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[[email protected] tmp]# let str--; Echo

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[[email protected] tmp]# let--str; Echo

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You can use $ (()) If you want the operation to be in the command, i.e. no additional assignment behavior is required.

Echo $ ((str++))

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Echo $ ((str--))  #从这个结果中是否发现了问题?

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Echo $ ((str--))

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Echo $ ((str++))  #还有这个结果

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Echo $ ((str++))

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I do not know whether it is my calculation, or the question of $ (()), if it is $ (()) suffix-plus (i++) and suffix-decrement (i--), then after the suffix self-increment, then the suffix will again perform a self-increment behavior, in contrast, the self-increment is also.

However, using $ (()) to calculate prefix self-increment and self-subtraction transformations is no problem, and let self-decrement is no problem.

Echo $ ((--STR))

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Echo $ ((--STR))

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Echo $ ((++str))  #结果正常

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Echo $ ((++STR))

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Echo $ ((--STR))

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You can also use [].

echo $[str= $str +6]  #在 [] Use the variable symbol $

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Echo $[str=str+6]  #[] does not use the $ symbol

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However, if $[$str =str+6] or $[$str = $str +6] An error will occur.

echo $[$str =str+6]

-bash: 24=str+6: Attempted assignment to Non-variable (Error token is "=str+6")

echo $[$str = $str +6]

-bash: 24=24+6: Attempted assignment to Non-variable (Error token is "=24+6")

Summarize the operation method of the variable:

[Email protected] tmp]# i= [[email protected] tmp]# Let I=i-1[[email protected] tmp]# Let i-=1[[email protected] tmp]# I=$ ((-1)) [[email protected] tmp]# I1  ]  #中括号隔壁必须写空格 [[email protected] tmp]# i1 ]

Shell Script Raiders (learning notes)--1.5 to perform mathematical operations