Shell Loop Statement Usage

Loop statements are often used when writing shell scripts. Here a simple summary of the commonly used 3 kinds of circular statements, so that later can quickly reference to write, nonsense do not say, start Demo:

　　1, for

Used mainly for: traversing elements in a known sequence

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If [$#-ge 1]; then path=$@ else path=*.sh fi

For I-$path do ls-lh $i The done note: optional in the For loop's in list, and if omitted, the shell traverses the entire command-line argument, at which point for I is equivalent to "$@"

　　Give me another example of the usage for:

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For i in ' SEQ 1 9 ' does echo $i done Note: For in can and ' with $ ()

Give me another example of the usage for:

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For i in {a......z} does echo $i done

　　Note:for-in braces {} have automatic completion function, curly braces and to be padded between the contents can not have spaces, to be filled with the contents of the two ... Connected, there should be no spaces and then give a for usage example:

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for ((I=1; i<=10; i++))

Do echo $i A done reminder: This is mainly used (())

　　2, while

Mainly used for: when a certain condition is established, always carry out

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Cnt=9

While [$cnt-ge 0] do echo $ ((cnt--))

Done

Note: 1, arithmetic operations need to be placed in the brackets of $ (())

2, for the arithmetic operation of the variable, in the $ (()), the variable in front does not need $

　　3, unitl

Used mainly for: when a condition is set up, stop executing

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Cnt=9 until [$cnt-lt 0] do echo $cnt cnt=$ ((cnt-1))

Done

　　Note: when assigning a value to a variable, do not add $ to the front