Understanding parameters in a function - bash

Question

I found this function:
findsit()
{
OPTIND=1
local case=""
local usage="findsit: find string in files.
Usage: fstr [-i] \"pattern\" [\"filename pattern\"] "
while getopts :it opt
do
case "$opt" in
i) case="-i " ;;
*) echo "$usage"; return;;
esac
done
shift $(( $OPTIND - 1 ))
if [ "$#" -lt 1 ]; then
echo "$usage"
return;
fi
find . -type f -name "${2:-*}" -print0 | \
xargs -0 egrep --color=always -sn ${case} "$1" 2>&- | more
}
I understand the output and what it does, but there are some terms I still don't understand and find it hard to find a reference, but believe they would be useful to learn in my programming. Can anyone quickly explain them? Some don't have man pages.
local
getopts
case
shift
$#
${2:-*}
2>&-
Thank you.

Answer 1

local: Local variable. Let's say you had a variable called foo in your program. You call a function that also has a variable foo. Let's say the function changes the value of foo.
Try this program:
testme()
{
foo="barfoo"
echo "In function: $foo"
}
foo="bar"
echo "In program: $foo"
testme
echo "After function in program: $foo"
Notice that the value of $foo has been changed by the function even after the function has completed. By declaring local foo="barfoo" instead of just foo="barfoo", we could have prevented this from happening.
case: A case statement is a way of specifying a list of options and what you want to do with each of those options. It is sort of like an if/then/else statement.
These two are more or less equivelent:
if [[ "$foo" == "bar" ]]
then
echo "He said 'bar'!"
elif [[ "$foo" == "foo" ]]
then
echo "Don't repeat yourself!"
elif [[ "$foo" == "foobar" ]]
then
echo "Shouldn't it be 'fubar'?"
else
echo "You didn't put anything I understand"
fi
and
case $foo in
bar)
echo "He said 'bar'!"
;;
foo)
echo "Don't repeat yourself!"
;;
foobar)
echo "Shouldn't it be 'fubar'?"
;;
*)
echo "You didn't put anything I understand"
;;
esac
The ;; ends the case option. Otherwise, it'll drop down to the next one and execute those lines too. I have each option in three lines, but they're normally combined like
foobar) echo "Shouldn't it be 'fubar'?";;
shift: The command line arguments are put in the variable called $*. When you say shift, it takes the first value in that $* variable, and deletes it.
getopts: Getopts is a rather complex command. It's used to parse the value of single letter options in the $# variable (which contains the parameters and arguments from the command line). Normally, you employ getopts in a while loop and use case statement to parse the output. The format is getopts <options> var. The var is the variable that will contain each option one at a time. The specify the single letter parameters and which ones require an argument. The best way to explain it is to show you a simple example.
$#: The number of parameters/arguments on the command line.
${var:-alternative}: This says to use the value of the environment variable $var. However, if this environment variable is not set or is null, use the value alternative instead. In this program ${2:-*} is used instead. The $2 represents the second parameter of what's left in the command line parameters/arguments after everything has been shifted out due to the shift command.
2>&-: This moves Standard Error to Standard Output. Standard Error is where error messages are put. Normally, they're placed on your terminal screen just like Standard Output. However, if you redirect your output into a file, error messages are still printed to the terminal window. In this case, redirecting the output to a file will also redirect any error messages too.

Answer 2

Those are bash built-ins. You should read the bash man page or, for getopts, try help getopts
One at a time (it's really annoying to type on ipad hence switched to laptop):
local lets you define local variables (within the scope of a function)
getopts is a bash builtin which implements getopt-style argument processing (the -a, -b... type arguments)
case is the bash form for a switch statement. The syntax is
case: case WORD in [PATTERN [| PATTERN]...) COMMANDS ;;]... esac
shift shifts all of the arguments by 1 (so that the second argument becomes the first, third becomes second, ...) similar to perl shift. If you specify an argument, it will shift by that many indices (so shift 2 will assign $3 -> $1, $4 -> $2, ...)
$# is the number of arguments passed to the function
${2:-*} is a default argument form. Basically, it looks at the second argument ($2 is the second arg) and if it is not assigned, it will replace it with *.
2>&- is output redirection (in this case, for standard error)