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This article mainly introduces the relevant knowledge of "how to use for cycle in Linux shell". The editor shows you the operation process through an actual case. The operation method is simple, fast and practical. I hope this article "how to use for cycle in Linux shell" can help you solve the problem.

For is a commonly used loop structure in Linux shell. Its main function is to assign values to variables from the elements in the loop list. Each assignment executes a loop, and done marks the end of a loop.

The list for loop statement is used to execute a set of commands for a known number of times. The basic format of the statement is as follows

For variable in (list) do command command... In done, the command between do and done becomes the body of the loop and is executed the same number of times as the number of constants or strings in the list list. When executing a for loop, first assign the first constant or string of the list list after in to the loop variable, then execute the loop body; then assign the second constant or string in the list list to the loop variable, and execute the loop body again. This process continues until there are no other constants or strings in the list list, and then the sequence of commands after the done command is executed.

Ex1, the case where the list list is constant in the for loop

#! / bin/bash # use the list for loop to display five welcome operations for variable in 1 2 3 4 5 do echo "Hello, welcome $variable times" done this example loop is often used for counting, and the range is limited to between 1 and 5. The following is the result of the script execution. Since 5 parameters are listed in the list after in, you can see that the script performs 5 welcome actions.

[zhangqi@localhost shellscript] $sh for_ex1.sh Hello, welcome 1 times Hello, welcome 2 times Hello, welcome 3 times Hello, welcome 4 times Hello, welcome 5 times [zhangqi@localhost shellscript] $Linux shell supports the use of abbreviated counting in the list for loop. We slightly improve the script.

Ex2, the list is in abbreviated form

#! / bin/bash # using the list for loop to display five welcome operations for variable in {1.. 5} do echo "Hello, welcome $variable times" done, the result is the same as script 1

[zhangqi@localhost shellscript] $sh for_ex2.sh Hello, welcome 1 times Hello, welcome 2 times Hello, welcome 3 times Hello, welcome 4 times Hello, welcome 5 times [zhangqi@localhost shellscript] $above example, we will skim 1x5 so that it can normally output the same result as example 1.

Ex3, the list is abbreviated

#! / bin/bash # use the list for loop to display 5 welcome operations for variable in $(seq 1 5) do echo "Hello, welcome $variable times" doneseq command is the external command preset by Linux, which is generally used to simplify the writing of a bunch of numbers. You can refer to the seq of common commands in linux.

After execution, the result is the same as above, so it will not be repeated.

Ex4, which implements the list by step-by-step jump

#! / bin/bash # use the list for loop to display 5 welcome operations for variable in {1... 5... 2} do echo "Hello, welcome $variable times" donein {1... 5. 2} to achieve the number within 1 to 5, jump according to step 2

Run it and take a look at the results

[zhangqi@localhost shellscript] $sh for_ex4.sh Hello, welcome 1 times Hello, welcome 3 times Hello, welcome 5 times [zhangqi@localhost shellscript] $ex5, jumping mode is expressed in seq

[zhangqi@localhost shellscript] $cat for_ex5.sh #! / bin/bash # use the list for loop to display 5 welcome operations for variable in $(seq 1 25) do echo "Hello, welcome $variable times" done [zhangqi@localhost shellscript] $sh for_ex5.sh Hello, welcome 1 times Hello, welcome 3 times Hello, welcome 5 times [zhangqi@localhost shellscript] $ex6, using a string to represent the list

[zhangqi@localhost shellscript] $cat for_ex6.sh #! / bin/bash # use the list for loop to display the corresponding English for day in Monday Tuesday Wednesday Thursday Friday Saturday Sunday do echo "$day" done [zhangqi@localhost shellscript] $sh for_ex6.sh Monday Tuesday Wednesday Thursday Friday Saturday Sunday [zhangqi@localhost shellscript] $ex7 from Monday to Sunday, and use the command to express the list

[zhangqi@localhost shellscript] $cat for_ex7.sh #! / bin/bash # use the command to print the array for variable in `ls / `do echo "Every directory is $variable" done [zhangqi@localhost shellscript] $sh for_ex7.sh Every directory is bin Every directory is boot Every directory is dev Every directory is etc Every directory is home Every directory is lib Every directory is lost+found Every directory is media Every directory is mnt Every directory is opt Every directory is proc Every directory is root Every directory is sbin Every directory is selinux Every directory is srv Every directory is sys Every directory is tmp Every directory is usr Every directory is var [zhangqi@localhost shellscript] $the command format here can be $(command) or command If the effect is the same, there will be no more display here.

Ex8, the list is realized by passing parameters through script

[zhangqi@localhost shellscript] $cat for_ex8.sh #! / bin/bash echo "number of arguments is $#" echo "What you input is:" # use the command to print the array for argument in "$*" do echo "$argument" done [zhangqi@localhost shellscript] $sh for_ex8.sh 1 hello shell number of arguments is 3 What you input is: 1 hello shell [zhangqi@localhost shellscript] $, you can see that the parameter list can be a number or a string But the input is separated by spaces, and if there is a space, the script executes as if there is another parameter.

This is the end of the content about "how to use the for loop in Linux shell". Thank you for reading. If you want to know more about the industry, you can follow the industry information channel. The editor will update different knowledge points for you every day.

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