sample session about “brace and tilde” expansions in Bash

$ls
trueangle
$echo hello > a.txt
$echo killo > b.txt
$cat {a,b}.txt
hello
killo
$pwd
/home/jeffrin/temp
$cd  ~
$pwd
/home/jeffrin
$cd tr
trueangle/     trueangle.old/ 
$pwd
/home/jeffrin
$cd -
/home/jeffrin/temp
$pwd
/home/jeffrin/temp
$ls
a.txt  b.txt  trueangle
$