#!/bin/sh

#   Yes, you can execute this whole script for demonstration.  You can
#   also give it an argument - which defaults to 15.

#   Of course you also remember comments, the here document, and the :
#   command, right? :-)  Okay, so I effectively (but not literally)
#   comment out the part between the pairs of __EOT__ without having to
#   individually comment out most or all the lines in the section.

>>/dev/null 2>&1 : << \__EOT__

#   if syntax:

if list; then list; [ elif list; then list ] ... [ else list; ] fi

    #   here the square bracket ([]) characters aren't meant literally,
    #   but rather indicate the enclosed portion is optional
    #   the ... indicates the preceding (optional) portions can be
    #   repeated zero or more times

    #   we need whitespace (one or more spaces, tabs, or newlines)
    #   between if and list, newline or ; between list and then, newline
    #   or ; after subsequent lists, and whitespace between each elif or
    #   else and the list that immediately follows it.

__EOT__

# if $1 is not set, we set it to 15
# "${1-15}" gives us "$1" if $1 is set, "15" otherwise
# we then use set to set that as our first (and now only) positional parameter
set -- "${1-15}"
# as side effect, we unset an other positional parameters
# you can execute this script with arguments, to change $1 from the default
# value of 15

# Typical fairly readable use in scripts:
# (the test logic is reversed to more defensively handle relatively arbitrary
# argument passed to us)
if [ 15 -eq "$1" ]; then
	echo "equals 15"
elif [ 15 -lt "$1" ]; then
	echo "greater than 15"
elif [ 15 -gt "$1" ]; then
	echo "less than 15"
else
	1>&2 echo "I'm confused, you gave me: $1"
fi

# somewhat less readable version with minimum whitespace and no semicolons:
if [ 15 -eq "$1" ]
then
echo "equals 15"
elif [ 15 -lt "$1" ]
then
echo "greater than 15"
elif [ 15 -gt "$1" ]
then
echo "less than 15"
else
1>&2 echo "I'm confused, you gave me: $1"
fi

# without newlines:
if [ 15 -eq "$1" ]; then echo "equals 15"; elif [ 15 -lt "$1" ]; then echo "greater than 15"; elif [ 15 -gt "$1" ]; then echo "less than 15"; else 1>&2 echo "I'm confused, you gave me: $1"; fi

# somewhat less readable version with minimum whitespace and no newlines
# within the command:
if [ 15 -eq "$1" ];then echo "equals 15";elif [ 15 -lt "$1" ];then echo "greater than 15";elif [ 15 -gt "$1" ];then echo "less than 15";else 1>&2 echo "I'm confused, you gave me: $1";fi