If you enclose a group of commands in parenthesis then this runs the commands in a subshell environment
The Shell state will be different than the parent
For example the current directory and variable values will not be the same
But values such as $$ which is the current Process ID will be the same
Subshells are almost always executed in a separate process
The Parentheses are specially treated
Curly Braces { ... } enclose a code block
The braces are recognized in keyword contexts
Make sure to put a semicolon or newline before the closing brace
Any state will be shared with the main script
Like the current directory or variables
tar -cf - . | (cd ~/tmp/copy ; tar -xpvf -)This will use the current directory contents and run the tar command but this will be piped into a subshell process
echo $$This will print the current process ID for the shell
(echo $$)This will print the same number because it is shared between parent shell and subshell
test -d ~/tmp/copy && { cd ~/tmp/copy ; }This will test if the directory ~/tmp/copy exists and if so will execute within the code block
test -d ~/tmp/copy && ( cd ~/tmp/copy ; pwd )Notice with this command the subshell does indeed go to ~/tmp/copy but the parent does not actually do so
for i in this is a code block here
{
echo $i
}This for loop is run in a code block
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