What do these symbols "$@">/dev/null 2>&1" after a command mean? [duplicate]

Solution 1:

"$@"

"$@" is equivalent to "$1" "$2" ... (the positional parameters to the command, good to use when there are special characters, for example spaces, within the parameters).

From man bash:

   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 is not within double quotes,  each  positional  parameter
              expands  to  a  separate  word.  In contexts where it is performed,
              those words are subject to  further  word  splitting  and  pathname
              expansion.   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" "$2" ...  If
              the double-quoted expansion occurs within a word, the expansion  of
              the first parameter is joined with the beginning part of the origi‐
              nal word, and the expansion of the last parameter  is  joined  with
              the  last  part of the original word.  When there are no positional
              parameters, "$@" and $@ expand to nothing (i.e., they are removed).

>

Redirection of standard output to a file

/dev/null

The special file that means that the output will be redirected 'nowhere' in other words not written anywhere.

See man null for more details.

2>

Redirection of error output to a file

2>&1

Redirection of error output to standard output

From man bash:

   Note that the order of redirections is significant.  For example, the com‐
   mand

          ls > dirlist 2>&1

   directs both standard output and standard error to the file dirlist, while
   the command

          ls 2>&1 > dirlist

   directs only the standard output to file  dirlist,  because  the  standard
   error  was  duplicated from the standard output before the standard output
   was redirected to dirlist.

Solution 2:

• "$@": all arguments of a script or function call.
• >: means redirect stdout (same as 1>).
• >/dev/null: means redirect stdout to /dev/null, meaning just trash the output.
• 2>&1 Redirect errout (2>) to stdout (&1).