The request was, if you have an absolute path, how can SQL extract the filename from the path? One approach is found below.

Extracting the IFS filename from an absolute path name.sql

--
-- Subject: Extracting the IFS file name from a path, using regular expression built-in functions
-- Author: Scott Forstie  
-- Date  : September 27, 2021
-- Features Used : This Gist uses regexp_count, regexp_instr, substr, and SQL PL
--
-- Function - The request was, if you have an absolute path, how can SQL extract the filename from the path?
--            One approach is found below.
--
--

values regexp_count('/usr/scottf/subdir1/subdir2/subdir3/anifsfile.sfx', '/');
--
-- Returns:
-- 6
stop;

values regexp_instr(
    '/usr/scottf/subdir1/subdir2/subdir3/anifsfile.sfx', '/', 1, 
    regexp_count('/usr/scottf/subdir1/subdir2/subdir3/anifsfile.sfx', '/'));
--
-- Returns:
-- 36   
--
--  '/usr/scottf/subdir1/subdir2/subdir3/anifsfile.sfx', '/', 1, 
--   123456789012345678901234567890123456
--
stop;

--
-- Put it all together
--
values substr('/usr/scottf/subdir1/subdir2/subdir3/anifsfile.sfx', 
              regexp_instr('/usr/scottf/subdir1/subdir2/subdir3/anifsfile.sfx', '/', 1, 
                           regexp_count('/usr/scottf/subdir1/subdir2/subdir3/anifsfile.sfx', '/'))+1);
--
-- Returns:
-- anifsfile.sfx
--
stop;

--
-- Encapsulate the logic within a Scalar UDF
--
create or replace function systools.Extract_IFS_filename (
      p_pathname dbclob(16m) ccsid 1200
  )
  returns dbclob(10000) ccsid 1200
  deterministic
  no external action
  reads sql data
  not fenced
  set option COMMIT = *NONE
  begin
    return substr(p_pathname, regexp_instr(p_pathname, '/', 1, regexp_count(p_pathname, '/')) + 1);
  end;
stop;

values  systools.Extract_IFS_filename ('/usr/scottf/subdir1/subdir2/subdir3/anifsfile.sfx');
--
-- Returns:
-- anifsfile.sfx

Great example, for using the REGEXP functions!
But for determining the IFS File Name there is IMHO an easier way, just by using the Locate_In_String Function:
Values(Substr('/usr/scottf/subdir1/subdir2/subdir3/anifsfile.sfx',
Locate_In_String('/usr/scottf/subdir1/subdir2/subdir3/anifsfile.sfx', '/', -1) + 1));

With SQL, its not uncommon to have multiple solutions to choose from.
Perhaps in our next Db2 for i Ping/Pong match, we can each have a turn explaining why we prefer our approach.

When is our next Db2 for i Ping/Pong? CEC? POW3R?

An excellent question indeed!
I only wish it were in person and soon.

If the goal is brevity, I usually prefer regexp_replace() which is somewhat equivalent to how I used sed in bash. It works by selecting the longest string at the end of the value which does not contain a slash. It also handles a filename with no path correctly.

values regexp_replace('/usr/scottf/subdir1/subdir2/subdir3/anifsfile.sfx','.*?([^/]+)$','\1');

Thanks for sharing your technique.

Since we're at it, why not give added value?

with pth as (
select '/usr/scottf/subdir1/subdir2/subdir3/anifsfile.sfx'
as path from sysibm.sysdummy1)

select
substr(path, 1, regexp_instr(path,'/', 1, regexp_count(path,'/')))
as folder,
substr(path, regexp_instr(path,'/', 1, regexp_count(path,'/'))+1)
as file
from pth