Three Zsh Tips

To expand environment variables in the prompt, make sure setopt prompt_subst is in effect.  This is the default in sh/ksh modes, but not zsh mode.

To automatically report the time a command took if it consumes more than a certain amount of CPU time, set REPORTTIME to the limit in seconds.  That is, REPORTTIME=1 (I am impatient) will act like I ran the command with time originally, if it consumes more than a second.

There’s a similar REPORTMEMORY variable to show the same (!) stats for processes that use more than the configured amount of memory during execution.  (Technically, RSS, the Resident Set Size.)  The value is in kilobytes, so REPORTMEMORY=10240 will print time statistics for processes larger than 10 MiB.  Relatedly, one should configure TIMEFMT to include “max RSS %M” in order to actually show the value that made the stats print.

Note that REPORTTIME and REPORTMEMORY do not have to be exported, as they’re only relevant to the executing shell.

# in ~/.zshrc
REPORTTIME=3
REPORTMEMORY=40960
TIMEFMT='%J  %U user %S system %P cpu %*E total; max RSS %M'

Sources: REPORTTIME and REPORTMEMORY are documented in the zshparam man page.  Prompt expansion is described in zshmisc, and the prompt_subst option is in zshoptions.