new_var=10
x=456
echo $2
echo $USERNAME
${HOMEDIR}
((a+=b))
((a*=b))
((a/=b))
((a%=b))
((a|=b))
((a^=b))
((a==b))
((a!=b))
((a<=b))
((a>=b))
$((a<<b))
$((a>>b))
$((a&&b))
$((a||b))
${a:-b}
${a:=b}
${a:+b}
${a:?b}
${a##*/}
${a%%.*}
${a^^}
${a,,}
${!a}
${a[@]}
ls -x
ls --color