Confuse how to use "$1" vs "$@"

ETC Homework & Coursework Questions
1

I am confuse how to use the commands as follow:

grep "$1" /location of a file 
vs
grep "$@" /location of a file

What are differences between these two types of search?
Where can I read to get more knowledge about how to use $1 and $@?

Thank you,

Scopiop

2

$1 represents the first positional parameter, and $@ represents all of them.

Here's an extract from the bash manual page on my system:

   Positional Parameters
       A positional parameter is a parameter denoted by one or more digits, other than the single digit 0.  Positional
       parameters  are  assigned  from  the  shell's arguments when it is invoked, and may be reassigned using the set
       builtin command.  Positional parameters may not be assigned to  with  assignment  statements.   The  positional
       parameters are temporarily replaced when a shell function is executed (see FUNCTIONS below).

       When  a  positional parameter consisting of more than a single digit is expanded, it must be enclosed in braces
       (see EXPANSION below).

   Special Parameters
       The shell treats several parameters specially.  These parameters may only be referenced; assignment to them  is
       not allowed.
       *      Expands  to  the  positional  parameters,  starting  from  one.  When the expansion occurs within double
              quotes, it expands to a single word with the value of each parameter separated by the first character of
              the IFS special variable.  That is, "$*" is equivalent to "$1c$2c...", where c is the first character of
              the value of the IFS variable.  If IFS is unset, the parameters are separated  by  spaces.   If  IFS  is
              null, the parameters are joined without intervening separators.
       @      Expands  to  the  positional  parameters,  starting  from  one.  When the expansion occurs within double
              quotes, each parameter expands to a separate word.  That is, "$@" is equivalent to "$1" "$2" ...  If the
              double-quoted  expansion  occurs  within a word, the expansion of the first parameter is joined with the
              beginning part of the original word, and the expansion of the last parameter is  joined  with  the  last
              part  of  the  original  word.   When  there are no positional parameters, "$@" and $@ expand to nothing
              (i.e., they are removed).
3

bakunin