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From: Greg Wooledge <wooledg@eeg.ccf.org>
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Subject: Re: Sequence Brace Expansion Crash
Date: Mon, 4 Jun 2018 09:02:33 -0400
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On Sat, Jun 02, 2018 at 09:18:14PM -0700, Thomas Fischer wrote:
> Repeat-By:
> echo {a..z}{a..z}{a..z}{a..z}{a..z}{a..z}

26^6 = 308915776 words of 6 bytes each, plus however much overhead is
involved in constructing a list of 308915776 strings.

You've probably gone well over 2 GB of virtual memory for this expansion.

When you're trying to a few GB of data to stdout, use nested loops
instead of a single brace expansion that needs to generate the entire
list in memory.

for a in {a..z}; do
  for b in {a..z}; do
    for c in {a..z}; do
      for d in {a..z}; do
        for e in {a..z}; do
          for f in {a..z}; do
            printf '%s%s%s%s%s%s\n' "$a" "$b" "$c" "$d" "$e" "$f"
          done
        done
      done
    done
  done
done

And if that's too slow in bash, consider using awk or perl or C.