[jayhemnani9910]

GNU sed's \` and \' match only at the start and end of the pattern space, also with the M flag where ^ and $ match at every line. Here they are passed to the regex engine as is, which reads them as an escaped backtick and quote, so they never match:

$ printf 'ab\ncd\n' | ./target/debug/sed 's/\`./X/g'
ab
cd
$ printf 'ab\ncd\n' | /usr/bin/sed 's/\`./X/g'    # GNU sed 4.9
Xb
Xd

The parser now writes them as \A and \z, which both regex engines know. That also sends patterns like s/\`a/X/ to the regex matcher instead of the literal one, the same way \b already does. Inside brackets, in the replacement, as the delimiter and with --posix they stay literal characters, as before.

Tests: test_buffer_start_and_end_anchors covers s/\`./X/g, the M flag case (N;s/\`/>/Mg;s/\'/</Mg gives >ab\ncd<) and the literal-only case, with GNU sed 4.9's output. It fails without the change. cargo test: 747 passed (746 on main plus the new one), clippy and rustfmt clean. I also checked ERE mode, addresses, the C locale, back-references next to an anchor, ` and ' as delimiters and --posix against GNU sed: all the same.

[Copilot]

Copilot was unable to review this pull request because the user who requested the review has reached their quota limit.

An organization owner can choose the repository organization as the billing source for reviews requested by members with a paid Copilot license. Learn about Copilot code review billing. Review the Copilot code review billing settings.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 94.94%. Comparing base (3e86e42) to head (77e6121).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #613   +/-   ##
=======================================
  Coverage   94.93%   94.94%           
=======================================
  Files          14       14           
  Lines        7292     7295    +3     
  Branches      434      434           
=======================================
+ Hits         6923     6926    +3     
  Misses        368      368           
  Partials        1        1           

Flag	Coverage Δ
macos_latest	96.46% <100.00%> (+<0.01%)	⬆️
ubuntu_latest	96.40% <100.00%> (+<0.01%)	⬆️
windows_latest	0.00% <0.00%> (ø)

Flags with carried forward coverage won't be shown. Click here to find out more.

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.