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This article mainly talks about "what are the linux shell process control statements". Interested friends may wish to have a look. The method introduced in this paper is simple, fast and practical. Next let the editor to take you to learn "what are the linux shell process control statements?"

I. shell conditional statement (if usage)

If statement structure [if/then/elif/else/fi]

The code is as follows:

If conditional test statement

Then

Action

[elif condition

Action

Else

Action

]

Fi

If the conditional test statement is not very clear, you can refer to: linux shell logical operator, logical expression detailed explanation

The shell command, which can be divided by semicolon or newline character. If you want to write more than one command per line, you can split it with ";".

Such as:

The code is as follows:

[chengmo@centos5] $axi5bot if [[a-gt 4]]; then echo 'ok';fi

Ok

Example: (test.sh)

The code is as follows:

#! / bin/sh

Scores=40

If [$scores-gt 90]; then

Echo "very good!"

Elif [$scores-gt 80]; then

Echo "good!"

Elif [$scores-gt 60]; then

Echo "pass!"

Else

Echo "no pass!"

Fi

Conditional tests include: [[]], [], test. Note: [[]] is separated from variables by spaces.

2. Circular statement (for,while,until usage):

1.for recycling method (for/do/done)

Grammatical structure:

The code is as follows:

1.for... In statement

For variable in seq string

Do

Action

Done

Description: as long as the seq string is separated by space characters, each time for. When in reads, the values are read sequentially to the preceding variables.

Instance (testfor.sh):

The code is as follows:

#! / bin/sh

For i in $(seq 10); do

Echo $I

Done

Seq 10 produces 1 2 3. 10 spaces separate strings.

2.for ((assignment; condition; Operation statement))

The code is as follows:

For ((assignment; condition; Operation statement))

Do

Action

Done

Instance (testfor2.sh):

The code is as follows:

#! / bin/sh

For ((iTun1)

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