Old boy Education Day-2017-04-25: How to produce a child shell?

1. execute a shell scriptin the parent Shell to produce a child shell

test Environment:

Define a variable and output

[[email protected] ~]$ Str=123[[email protected] ~]$ echo $STR 123

write a test script and execute

[

[email protected] ~]$ cat Test.sh#!/bin/bashecho $STR [[email protected] ~]$./test.sh [[email protected] ~]$ export str[[e Mail protected] ~]$./test.sh123

A child shell cannot directly use a variable defined in the parent shell, and export is promoted to an environment variable

2. Execute a command in theparent Shell , add & at the end of the command to produce a child shell

[Email protected] ~]$ str=123; Str=abc[[email protected] ~]$ echo $STRabc [[email protected] ~]$ str=123; STR=ABC&[1] 16467[[email protected] ~]$ echo $STR 123[1]+ done STR=ABC

Define a variable Str Assignment 123, re-assignment ABC, the value of the result variable str is ABC, when the second assignment is added to the end of the &, the variable str value does not change, indicating that the second assignment is not in the current shell, it opens a child shell.

3. Use () to produce a child shell

[Email protected] ~]$ str=123&& (STR=ABC) && echo $STR 123

with the above case, the variable assignment in the () cannot modify the value of the previous variable, and also produces the child shell

4. execute a command with a pipeline in the parent shell

[[Email protected] ~] $STR =123| Str=456;echo $STR 123

print variables in a child shell

[Email protected] ~]$ str=123| {Str=456;echo $STR;} 55W

today is a day to accompany everyone's first day, look forward to your progress.

For questions and answers, please leave a comment in the blog comments section.

Index of the topic of the previous period

http://lidao.blog.51cto.com/3388056/1914205

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Old boy Education Day-2017-04-25: How to produce a child shell?