&> 1> 2> in bash /dev/null 1 is stdout, 2 is stderr, & is both? Can redirect into each other, e.g. 2>&1? Term is 'redirect' This also is the same as just the standard >, e.g. echo 'Hello' > test.txt What is >>?
Redirection operators allow control of where [[input and output streams]] should go. The following are some of the redirect operators in Bash:
> - redirect output, overwriting target if exists
>> - redirect output, appending instead of overwriting if target exists
&#> - redirect file descriptor #, where # is the identifier
< - redirect input
Streams can be referenced via their 'file descriptor identifier' (number). An ampersand is required if redirecting to another stream to reduce ambiguity.
command 1> out.log - outputs file descriptor 1 (stdout) to file.
Common redirects:
1> - redirects stdout only. This is also the same as simply doing >
2> - redirects stderr only
2>&1 - redirects stderr to stdout. The final output will contain both stdout and stderr output, if any.
&> - redirect stdout and stderr. This is also the same as the above 2>&1
If certain output isn't wanted, it can redirected to /dev/null which functions as a 'black hole' to silence the output.