extract the numeric parts from a string containing letters and digits

Try something like this... The approach is to use regsub command to swap every nonnumeric character for a space:

set inputLine "entry_rows_chunk2022vol34i9mn.txt"
regsub -all -nocase {[._a-z]} $inputLine { } digitsText
lassign $digitsText firstNum nextNum lastNum
puts "result = $firstNum $nextNum $lastNum"
# result = 2022 34 9

Using regexp command would probably be simpler, but I haven't worked that out yet.

References: regsub (https://www.tcl.tk/man/tcl/TclCmd/regsub.html), lassign (https://www.tcl.tk/man/tcl/TclCmd/lassign.html) and regexp (https://www.tcl.tk/man/tcl/TclCmd/regexp.html) (if you'd like to try)

I don't have an older Tcl version for testing, but give this a try:

set matches [regexp -all -inline {\d+} $entryText]
puts [join $matches]