Add additional documentation on shells that support read -u.
@@ -269,7 +269,9 @@ def run(input_file: KGTKFiles,
# Note: "read -u n", used below, is not supported by some shells.
# bash and zsh support it.
- # csh and tcsh do not.
+ # ash, csh, dash, and tcsh do not.
+ # The original standard Bourne shell, sh, does not.
+ # ksh might do it, if the FD number is a single digit.
cmd: str = "".join((
" { IFS= read -r header ; ", # Read the header line
" { printf \"%s\\n\" \"$header\" >&" + str(header_write_fd) + " ; } ; ", # Send the header to Python
