5.1 Built-in Commands
: null command
. source (read and execute) commands from a file
case case conditional loop
cd change the working directory (default is $HOME)
echo write a string to standard output
eval evaluate the given arguments and feed the result back to the shell
exec execute the given command, replacing the current shell
exit exit the current shell
export share the specified environment variable with subsequent shells
for for conditional loop
if if conditional loop
pwd print the current working directory
read read a line of input from stdin
set set variables for the shell
test evaluate an expression as true or false
trap trap for a typed signal and execute commands
umask set a default file permission mask for new files
unset unset shell variables
wait wait for a specified process to terminate
while while conditional loop