#define SQR(x) x*x		// bad

   SQR(9) -> 9*9 // ok

   SQR(3+2) -> 3+2*3+2 -> 3+6+2 = 11 // wrong

#define SQR(x) (x)*(x)		// bad

   1/SQR(3+2) -> 1/(3+2)*(3+2) -> (1/(3+2))*(3+2) // wrong

#define SQR(x) ((x)*(x))	// good

   1/SQR(3+2) -> 1/((3+2)*(3+2)) // ok

---

$ gcc x.f
gcc: error: x.f: Fortran compiler not installed on this system

$ chmod 755 x.sh y.sh

$ ls -l *.sh
-rwxr-xr-x 1 perry perry  15 Sep 12 17:16 x.sh
-rwxr-xr-x 1 perry perry 192 Sep 12 17:32 y.sh

$ cat x.sh
#! /bin/cat
hi

$ ./x.sh
#! /bin/cat
hi

$ cat y.sh
#! /bin/sh

echo "hi"

# z = 1 # bad
x=1 # no blanks in assignment
# while test "$x" -lt 7
while [ "$x" -lt 7 ]
do
  echo "$x"
  x=$((x+1))
done

while read line
do
  echo "line = $line"
done

$

# using dash echo:

$ echo "abc\na b c" | dash y.sh
hi
1
2
3
4
5
6
line = abc
line = a b c
$

---

# bash echo is non-standard, needs -e option to interpret backslash-escaped characters:

% dash
$ echo "a\nb"
a
b
$ bash
bash-4.2$ echo "a\nb"
a\nb
bash-4.2$ echo -e "a\nb"
a
b
bash-4.2$

# portable alternative to shell-specific echo: printf

$ printf "a\nb\n"
a
b
$