for x in 🍎 🍏 🍊
do
  echo ${x}
done

xs=(🍎 🍏 🍊)

for x in "${xs[@]}"
do
  echo ${x}
done

xs=(
🍎
🍏
🍊
)

for x in "${xs[@]}"
do
  echo ${x}
done

for dir in */
do
  echo $dir
done

for dir in **/
do
  echo $dir
done

echo $(realpath $0)

echo $(cd ${0%/*} && pwd -P)

echo ${0##*.}

exec -l $SHELL

date +%Y-%m-%d_%H-%M-%S

s=🍎🍏🍊
echo ${s#?} # 🍏🍊
echo ${s%?} # 🍎🍏

directory=~/Desktop/foo
[ -e ${directory} ] || mkdir -p ${directory}

echo 🍎 > /dev/null # redirects stdout only.
echo 🍎 2> /dev/null # redirects stderr only.
echo 🍎 &> /dev/null # redirects both stdout and stderr.

S=🍎_🍎
echo ${S/🍎} # _🍎
echo ${S//🍎} # _
echo ${S/🍎/🍊} # 🍊_🍎
echo ${S//🍎/🍊} # 🍊_🍊

cat << EOF > sample.txt
🍎
🍏
🍊
EOF

file --brief input.txt

rsync --archive src dst

$ cat input.txt
🍎
🍏
🍊

$ paste -s -d, input.txt
🍎,🍏,🍊

$ cat left.txt
🍎
🍏

$ cat right.txt
🍊
🍋

$ paste -d, left.txt right.txt
🍎,🍊
🍏,🍋

$ paste -d'\0' left.txt right.txt
🍎🍊
🍏🍋

my_function() {
  if [ $# -lt 2 ]
  then
    echo "Usage: $funcstack[1] <first-argument> <second-argument>"
    return
  fi

  echo "First argument: $1"
  echo "Second argument: $2"
}

$ my_function
Usage: my_function <first-argument> <second-argument>

$ my_function foo
Usage: my_function <first-argument> <second-argument>

$ my_function foo bar
First argument: foo
Second argument: bar

s=sample.txt
echo $s:r # sample
echo $s:e # txt

<command> &|

$ cat foo.txt
1,aa
2,bb
4,cc

$ cat bar.txt
1,xx
2,yy
5,zz

$ join -t, -1 1 -2 2 foo.txt bar.txt
1,aa,xx
2,bb,yy