index() #@ Print the position of $2 in $1
{ #@ USAGE: index STRING SUBSTRING
local idx
case $1 in
*$2*) idx=${1%%$2*}
echo $(( ${#idx} + 1 )) ;;
*) echo 0 ;;
esac
}

From Article

die() #@ Exit with error code and optional message
{ #@ USAGE: die RETURN_CODE [MESSAGE]
result=$1
shift
[ -n "$*" ] && printf "%s\n" "$*" >&2
exit "$result"
}

From Article

overlay() #@ Place SUBSTRING over STRING beginning at OFFSET 
{ #@ USAGE: overlay VARNAME SUBSTRING OFFSET 
local varname=$1 substr=$2 start=$3 string 
eval "string=\${$varname}" 
left=${string:0:start} 
right=${string:start+${#substr}} 
printf -v "$varname" %s%s%s "$left" "$substr" "$right" 
}

From Article

asc() #@ Print the ASCII value of the first character of each argument 
{ #@ USAGE: asc STRING ... 
for char 
do 
printf "%d${EOV-\n}" "'$char" 
done
}

From Article

revword() #@ print each argument with bytes reversed
for w
do
len=${#w}
w2=
n=0
while (( ${#w2} < len ))
do
w2=${w:n++:1}$w2
done
printf "%s\n" "$w2"
done

From Article