On Tue, Aug 16, 2022 at 08:25:12AM +0100, Tixy wrote: > On Mon, 2022-08-15 at 21:05 -0400, Timothy M Butterworth wrote: > > > > > Thanks for the clarification. `echo 1 > sudo /proc/sys/vm/drop_caches` > > seems to work just fine. > > It doesn't, as Tomas pointed out it creates a file called 'sudo' and > puts a '1' in it.
The following two commands are equivalent: echo 1 > sudo /proc/sys/vm/drop_caches echo 1 /proc/sys/vm/drop_caches > sudo The file "sudo" will have "1 /proc/sys/vm/drop_caches" in it, because echo received two arguments. Redirections may appear anywhere in a "simple" command. It's conventional to write them at the end of the command, but the shell permits them to be anywhere. This is a standard feature of all POSIX shells, by the way. Not a bash extension. Redirections must appear at the end of "compound" commands, which are basically anything with internal shell syntax -- if, case, while, and so on. It may be desirable to try to write something like: < inputfile while read -r line; do ... done but it's not allowed. You have to write it as: while read -r line; do ... done < inputfile Or, explicitly open the input file on a new FD (file descriptor), and close it afterward: exec 3< inputfile while read -r line <&3; do ... done exec 3<&-
