Subshells and Subprocesses¶

Subprocesses¶

What are Subprocesses?¶

A subprocess is a child process spawned by a parent process. When you run an external command in the shell, it usually spawns a subprocess. Builtins do not spawn subprocesses.

Intricacies:

Isolation: Subprocesses are isolated from the parent process, meaning they don't share variables or states.
Resource Overhead: Spawning a subprocess consumes more resources compared to running a builtin.

Use Cases: 1. Running External Programs: Anytime you run a program that's not a shell builtin, you're spawning a subprocess.

grep "pattern" file.txt

Pipelines: Each command in a pipeline runs in its own subprocess.
```
ls | grep txt
```

Subshells¶

What are Subshells?¶

A subshell is a child shell process spawned from a parent shell. Subshells inherit environment variables and settings from the parent shell but don't affect the parent when changed.

Intricacies:

Environment Isolation: Changes to variables in a subshell don't affect the parent shell.
Syntax: Subshells are often invoked using parentheses ().

Use Cases:

Grouping Commands: You can use a subshell to group commands and redirect their collective output.
```
(cd /some/dir && ls)
```
Isolated Environment: Running a script in a subshell to prevent it from affecting the current shell environment.
```
(source ~/.bashrc)
```