What does a dollar sign followed by an at-sign (@) mean in a shell script?
For example:
umbrella_corp_options $@
$@ is nearly the same as $*, both meaning "all command line arguments". They are often used to simply pass all arguments to another program (thus forming a wrapper around that other program).
The difference between the two syntaxes shows up when you have an argument with spaces in it (e.g.) and put $@ in double quotes:
wrappedProgram "$@"
# ^^^ this is correct and will hand over all arguments in the way
# we received them, i. e. as several arguments, each of them
# containing all the spaces and other uglinesses they have.
wrappedProgram "$*"
# ^^^ this will hand over exactly one argument, containing all
# original arguments, separated by single spaces.
wrappedProgram $*
# ^^^ this will join all arguments by single spaces as well and
# will then split the string as the shell does on the command
# line, thus it will split an argument containing spaces into
# several arguments.
Example: Calling
wrapper "one two three" four five "six seven"
will result in:
"$@": wrappedProgram "one two three" four five "six seven"
"$*": wrappedProgram "one two three four five six seven"
^^^^ These spaces are part of the first
argument and are not changed.
$*: wrappedProgram one two three four five six seven