brace expansion example.

README.md

@@ -107,6 +107,10 @@ Notes:
 
 - In Bash, note there are lots of kinds of variable expansion. Checking a variable exists: `${name:?error message}`. For example, if a Bash script requires a single argument, just write `input_file=${1:?usage: $0 input_file}`. Arithmetic expansion: `i=$(( (i + 1) % 5 ))`. Sequences: `{1..10}`. Trimming of strings: `${var%suffix}` and `${var#prefix}`. For example if `var=foo.pdf`, then `echo ${var%.pdf}.txt` prints `foo.txt`.
 
+- Shell brace expansion can help reduce having to re-type similar text.  The command `echo foo{,bar,baz}` will expand to
+`echo foo foobar foobaz`.  This is helpful when copying/renaming files such as `cp somefile{,.bak}` which expands to
+`cp somefile somefile.bak` or `mv some_{,absurdly_long_}filename` which expands to `mv some_filename some_absurdly_long_filename`
+
 - The output of a command can be treated like a file via `<(some command)`. For example, compare local `/etc/hosts` with a remote one:
 ```sh
       diff /etc/hosts <(ssh somehost cat /etc/hosts)