Loop statement instance in Shell

1. For Loop statements
Basic for loop of instance 1.1

#! /Bin/bash

For X in one two three four
Do
Echo number $ x
Done
 

Note: A "for" loop always receives a certain type of word list after the "in" statement. In this example, four English words are specified, but the word list can also reference files on the disk, or even file wildcards.
Instance 1.2

#! /Bin/bash
For X in/var/log /*
Do
# Echo "$ X is a file living in/var/log"
Echo $ (basename $ X) is a file living in/var/log
Done
 

Note: $ X obtains the absolute path file name. You can use the "basename" executable program to remove the preceding path information. If you only reference files in the current working directory (for example, if you enter "for X in *"), the generated file list will have no prefix for path information.
Instance 1.3 performs a for loop on location parameters

#! /Bin/bash
For thing in "[email protected]"
Do
Echo you typed $ {thing }.
Done

Instance 1.4 for loop generation cycles using seq

#! /Bin/bash
For J in $ (SEQ 1 5)
Do
Echo $ J
Done

Note: For a fixed number of cycles, you can use the seq command to implement them without variable auto-increment.

2. While loop statement
Instance 2.1 cyclically outputs numbers 1 to 10

#! /Bin/bash
Myvar = 1
While [$ myvar-le 10]
Do
Echo $ myvar
Myvar = $ ($ myvar + 1 ))
Done
 

Note: As long as the specified condition is true, the "while" statement will be executed.

3. Until loop statement
Instance 3.1 cyclically outputs numbers 1 to 10
The "until" statement provides the opposite functionality of the "while" Statement: as long as the specific conditions are false, they are repeated. The following is an "until" loop with the same function as the previous "while" loop.

#! /Bin/bash
Myvar = 1
Until [$ myvar-GT 10]
Do
Echo $ myvar
Myvar = $ ($ myvar + 1 ))
Done
 

 

It is also very important that the auto-increment of temporary variables will inevitably be used in the loop. for how to implement the auto-increment of variables in shell, see one of my previous

Variable auto-increment is often used when writing loops in Linux Shell. Now, let's summarize the auto-increment method of integer variables.
As I know, bash currently has five methods:
1. I = 'expr $ I + 1 ';
2. Let I + = 1;
3. (I ++ ));
4. I = $ [$ I + 1];
5. I = $ ($ I + 1 ))
A simple example is as follows:
#! /Bin/bash
I = 0;
While [$ I-lt 4];
Do
Echo $ I;
I = 'expr $ I + 1 ';
# Let I + = 1;
# (I ++ ));
# I = $ [$ I + 1];
# I = $ ($ I + 1 ))
Done

In addition, for a fixed number of cycles, the seq command can be used to achieve the implementation, without the need for variable auto-increment; the example is as follows:
#! /Bin/bash
For J in $ (SEQ 1 5)
Do
Echo $ J
Done

Http://www.linuxidc.com/Linux/2011-05/35893.htm