Grouping

A grouping command combines multiple commands so they are treated as a single command. This is useful for running several commands together in a pipeline or an and-or list.

Braces

Commands grouped in braces { ... } run in the current shell environment.

$ { echo "Hello"; echo "World"; }
Hello
World

A group can span multiple lines:

$ {
> echo "Hello"
> echo "World"
> }
Hello
World

Since { and } are reserved words, they must appear as separate words. See examples in the Keywords section.

Braces are especially useful for treating several commands as a single unit in pipelines or and-or lists:

$ { echo "Hello"; echo "World"; } | grep "Hello"
Hello

$ HOME=$PWD
$ test -f ~/cache/file || { mkdir -p ~/cache; > ~/cache/file; }

Subshells

Commands grouped in parentheses ( ... ) run in a subshell—a copy of the current shell environment. Changes made in a subshell do not affect the parent shell.

$ greeting="Morning"
$ (greeting="Hello"; echo "$greeting")
Hello
$ echo "$greeting"
Morning

Since ( and ) are operators, they can be used without spaces.

Compatibility

Some shells treat two adjacent ( characters specially. For best compatibility, separate open parentheses with a space to nest subshells:

$ ( (echo "Hello"))
Hello