subshell

The series of commands collected in parentheses runs in a subshell and does not affect the state of the current shell.

Here, the subshell command du -sh work | cut -f1 yields the total size of the work directory in a format compatible with pv.

Because the subshell is followed by a pipe, all the output of the subshell is sent to the next command in the pipeline.

The parenthesized series of commands is called a subshell.

Finally, the back quotes both interpret the variable and run the intermediate result as a subshell.

You can generally do this by running a list of commands in a subshell or by running a list of commands in the current shell.

Better yet, a subshell can contain another subshell, so expansions can be nested, too.

The parentheses effectively execute the statements in a subshell.

The use of the brackets ensures the commands are grouped and executed in a subshell.

Finally, we'll add an arbitrary 30-second sleep to ensure the command sequence finishes after the two subshells do.

By setting errexit, the subshell immediately terminates when the first command stops.

Because the subshell has so many uses, you might prefer to use it always instead of a combination or the back tick operators.

Listing 9 shows the same idea executed using a subshell.

In Listing 9, for example, if the first rsync failed, then the subshell would just continue and run the next command.

Effects of relaxation induced by excitation (or ionization) of inner subshell electrons on the wave functions and transition probabilities

Run a list of commands in a subshell