If bash pipeline commands run in subshell, why echo command can access the non-exported variables?

Question

Bash manual says "Each command in a pipeline is executed as a separate process (ie, in a subshell)". I test two simple commands.

Scene 1

cd /home/work
str=hello
echo $str | tee a.log

It outputs:

hello

It seems that echo command is not executed in a subshell, as it can access the non-exported variable $str .

Scene 2

cd /home/work
cd src | pwd
pwd

It outputs:

/home/work

Is looks like cd command is executed in a subshell, as it doesn't affect the working directory of original shello.

Can anyone explain why the behaviors are not consistent?

Answer 1

Can anyone explain why the behaviors are not consistent?

Well, because this is how it was designed. A "subshell" inherits the whole context, not only exported variables.

Bash manual says "Each command in a pipeline is executed as a separate process (ie, in a subshell)"

Bsah manual is available here . The sentence you are mentioning literally has a link to solve the mystery:

Each command in a pipeline is executed in its own subshell, which is a separate process (see Command Execution Environment).

Then you can check the "Command Execution Environment", from it (emphasis mine):

The shell has an execution environment, which consists of the following:

• ...
• shell parameters that are set by variable assignment...
• ...

...

Command substitution, commands grouped with parentheses, and asynchronous commands are invoked in a subshell environment that is a duplicate of the shell environment , ....

A subshell has all the environment (well, except traps). On the other hand commands:

When a simple command other than a builtin or shell function is to be executed, it is invoked in a separate execution environment that consists of the following. ....

• ...
• shell variables and functions marked for export, ...

If bash pipeline commands run in subshell, why echo command can access the non-exported variables?

Because a subshell inherits the parent environment, including all the non-exported variables.