Add e substitution flag

[PranavRJoshi]

This PR introduces e substitution mentioned in #404.

What this does

Implements the e substitute flag, which executes the result of the substitution as a shell command and replaces the pattern space with stdout (minus trailing newline).

$ echo a | ./target/release/sed  's/.*/echo hi/e'
hi

$ echo a | ./target/release/sed --posix 's/.*/echo hi/e'
sed: <script argument 1>:1:14: error: the 'e' substitute flag is not allowed with --posix or --sandbox

Changes

• src/sed/command.rs: new execute: bool field on Substitution
• src/sed/compiler.rs: 'e' arm in compile_subst_flags; rejected at compile time under --posix or --sandbox.
• src/sed/processor.rs: shell execution via /bin/sh -c after substitution

Tests

• Three new unit tests for the flag parser covering the intended path, --posix rejection, and --sandbox rejection.
• Full cargo test run passes.

[sylvestre]

please run rustfmt

[sylvestre]

/bin/sh ?
it won't work on windows

[PranavRJoshi]

Should I make it conditionally compile on UNIX-like system only and warn out the insufficient capabilities on Windows, or do I instead execute the cmd.exe for Windows? The latter one would still require conditional compilation, so i can add #[cfg] for UNIX-like and Windows.

[sylvestre]

nope, it is a cross platform project. this should be a tier-1 feature on Windows too

[codecov]

Codecov Report

❌ Patch coverage is 63.23529% with 25 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.72%. Comparing base (f783eb9) to head (9b1559f).

Files with missing lines	Patch %	Lines
src/sed/processor.rs	0.00%	25 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #413      +/-   ##
==========================================
+ Coverage   82.20%   82.72%   +0.51%     
==========================================
  Files          13       13              
  Lines        5542     5545       +3     
  Branches      310      307       -3     
==========================================
+ Hits         4556     4587      +31     
+ Misses        983      955      -28     
  Partials        3        3              

Flag	Coverage Δ
macos_latest	?
ubuntu_latest	82.72% <63.23%> (-0.28%)	⬇️
windows_latest	?

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[sylvestre]

please also add tests in tests/by-util/test_sed.rs

[PranavRJoshi]

Thanks for the guidance, will work into it.

[codspeed-hq]

Merging this PR will not alter performance

✅ 11 untouched benchmarks

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_{Comparing PranavRJoshi:main (7c2e7fd) with main (f783eb9)}