I'm using Ubuntu 23.10 x64. The time program has an -f flag but when I run it says -f command not found.
time -f "%Uu %Ss %er %MkB %C" ./countwords hamlet.txt
I'm trying to get the time program to output the memory use in addition to the default output.
You're probably running bash (or zsh), which has its own time command built-in so that it can time a whole pipeline and not just a single command:
type time
time is a shell keyword
help time
time: time [-p] pipeline
Report time consumed by pipeline's execution.
[…]
You can see that the built-in time command has only an optional -p flag.
If you want to use the external time command (/usr/bin/time) as shown in man time you will need to specify it explicitly:
command time -f '%Uu %Ss %er %MkB %C' ./countwords hamlet.txt
