What do these symbols "$@">/dev/null 2>&1" after a command mean?
"$@"
"$@"
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 $@ expand to nothing (i.e., they are removed).
>
Redirection of standard output to a file
/dev/null
The special file that means that the output will be redirected 'nowhere' in other words not written anywhere.
See man null
for more details.
2>
Redirection of error output to a file
2>&1
Redirection of error output to standard output
From man bash
:
Note that the order of redirections is significant. For example, the com‐
mand
ls > dirlist 2>&1
directs both standard output and standard error to the file dirlist, while
the command
ls 2>&1 > dirlist
directs only the standard output to file dirlist, because the standard
error was duplicated from the standard output before the standard output
was redirected to dirlist.
"$@"
: all arguments of a script or function call.>
: means redirectstdout
(same as1>
).>/dev/null
: means redirectstdout
to/dev/null
, meaning just trash the output.2>&1
Redirect errout (2>
) to stdout (&1
).