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s/// replacement: implement the \U \L \u \l \E case-conversion escapes

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@dedsec-terminal is already working on this.

Since Sep 15, 2026.

  • #557 by @dedsec-terminal — open

Assessment

Difficulty
3/5
Estimated time
1-2 days
Newbie friendliness
68/100
Issue type
Feature
Clarity
Mostly clear
Activity status
Active
Tech stack
rust
Domain
cli

Research direction

Start by running the replacement examples from the issue and locate uutils sed's replacement-text handling for s///. Implement support for \U, \L, \u, \l, and \E according to the GNU sed 4.9 results shown, then verify that all five examples produce the expected output.

Written by the indexing model from the issue text.

Description

good first issue

GNU sed supports case-conversion escapes in the replacement text of s///. None of them work in uutils sed today.

$ echo "abc def" | sed 's/b\(.*\)/\U&/'
script uutils sed GNU sed 4.9
s/b\(.*\)/\U&/ aUbc def aBC DEF
s/b\(.*\)/\u&/ aubc def aBc def
s/b\(.*\)/\L&/ a\Lbc def abc def
s/b\(.*\)/\l&/ a\lbc def abc def
s/b\(.*\)/\E&/ a\Ebc def abc def
Dominant language
Rust
Stars
110
Forks
36
Avg merge
1d 20h
Merged PRs (30d)
30

Getting set up

First steps

  1. Read the whole issue, then the project's contributing guide.
  2. Comment on the issue to say you are picking it up — it saves two people doing the same work.
  3. Fork the repository and make your change on a branch.
  4. Open a pull request that references the issue number.

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