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$1 is the first argument (filename1) $2 is the second argument (dir1)
#$ does "nothing", as # is starting comment and everything behind it on the same line is ignored (with the notable exception of the "shebang"). $# prints the number of arguments passed to a shell script (like $* prints all arguments). Follow this answer to receive notifications. edited Jul 9 at 13:55.
$2 is the second command-line argument passed to the shell script or function. Also, know as Positional parameters.
and >&2 means send the output to STDERR, So it will print the message as an error on the console. You can understand more about shell redirecting from those references: https://www.gnu.org/savannah-checkouts/gnu/bash/manual/bash.html#Redirections.
-z string True if the string is null (an empty string)
-z
string is null, that is, has zero length
String='' # Zero-length ("null") string variable.
if [ -z "$String" ]
then
echo "\$String is null."
else
echo "\$String is NOT null."
fi # $String is null.
test -z returns true if the parameter is empty (see man sh or man test).
The expression -z string is true if the length of string is zero.
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