i think i might have used strstr.
ok, i suppose you might have a file with 'does not exist' in its name,
but i can't say i lose much sleep over it.  could use strqstr to look outside quotes i suppose.

also, in

term% ls /sys/src/cm/db
ls: /sys/src/cm/db: '/sys/src/cm/db' does not exist

if it were

ls: /sys/src/cm/db: file does not exist: '/sys/src/cm/db' 

i'd find it a little odd to read, myself, although again i can't get too worked up about it.

in APE's case i suspect i'd settle for putting the most common error
strings at the front, on the grounds that most applications stop processing
once an error occurs anyhow, except for access/open/exec/stat when
used to search for something.  (so do the check for `does not exist' or
`no permission' early.)

is this worry the result of having profiled something important?
i vaguely remember from my time fighting it that gcc's cpp
causes the computer to wade through
pages of filth to get anywhere when doing the search lists for #include
but there's much more to slow you down in that thing.
perhaps like Linus's scheduler someone has finally done the decent thing?
anyhow: IS there a real cause to worry about APE's string -> errno
translation speed based on (say) a profile of an application, or is
it conjecture?