[chaliy]

Requested by Михайло · project thread

What changed

• Character escapes. \xHH, \dNNN, \oNNN and \cX now work in regexes, in replacements and in y. Each one always produces a literal character, so s/z/\x26/ inserts & rather than the match (GNU bug 30794 semantics).
• Escapes inside brackets. \t and \n work inside bracket expressions, so the common s/^[ \t]*// now strips tabs. Any other backslash inside brackets is still a literal member.
• -z mode. N, G and H join with NUL, and D and P split on NUL. With the M flag, ^ and $ also match around NUL.
• Unreadable input files. A file that cannot be read is reported (sed: can't read X: ...) and skipped. The remaining files are still processed, and the exit status is 2.
• Loop budget. The budget is now counted per input line read. Before, seq 3000 | sed '$!N;P;D' stopped after 1001 lines with a loop-limit warning. The uniq script (:b;$b;N;...;bb) had the same problem on long runs of duplicate lines. Loops that read no input (G;D, :a;s/^/x/;ta) are still stopped.

Why

These come from the sed lane of the pseudo-linus Debian oracle bench. The truncation of $!N;P;D was a real correctness bug on ordinary input sizes.

Before

$ seq 3000 | sed '$!N;P;D' | wc -l
sed: warning: branch/label loop limit (1000) reached on line 1002; output may be truncated
1001
$ echo z | sed 's/z/\x5cA/'      → x5cA
$ printf '\t\tb\n' | sed 's/^[ \t]*//'   → "\t\tb" (tabs kept)
Oracle bench: sed 94.2%

After

$ seq 3000 | sed '$!N;P;D' | wc -l
3000
$ echo z | sed 's/z/\x5cA/'      → \A
$ printf '\t\tb\n' | sed 's/^[ \t]*//'   → b
Oracle bench: sed 99.4%

Risk

Low. The DoS bound is kept: a loop is still capped unless it consumes input, and consuming input is bounded by the input size. L-SED-005 is updated to describe this.

Checklist

• Unit tests (positive and negative cases), compared against GNU sed 4.9 on the host
• cargo clippy -D warnings, cargo fmt; sed integration and spec tests pass
• Limitations and log updated

https://claude.ai/code/session_01VscpEzxtqpCKx5eRMpywNj

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