Parent shell and child Shell

Parentheses

The parentheses structure can force the command to run in the sub-shell. Its basic format is:

(

Command 1

Command 2

...

Command n

)

The N commands in parentheses are run in the sub-shell. After bash version 3, the internal variable bash_subshell is defined. This variable records the layer of the sub-shell..

The sub-shell can only inherit some attributes of the parent shell. However, the sub-shell cannot in turn change the attributes of the parent shell..

The attributes that the sub-shell can inherit from the parent shell are as follows:

Current working directory

Environment Variable

Standard input, standard output, and standard error output

All opened file identifiers

Ignored Signal

The attributes that the sub-shell cannot inherit from the parent shell are summarized as follows:

Shell variables except environment variables and variables defined in the. bashrc File

Unignored Signal Processing

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