Thanks for the bug report. I installed the attached, which should make
things clearer, albeit a bit more tersely than you suggested.
>From 53389bc57cc30ae1454ff48245cf63a703f02024 Mon Sep 17 00:00:00 2001
From: Paul Eggert <egg...@cs.ucla.edu>
Date: Thu, 3 Oct 2019 15:23:33 -0700
Subject: [PATCH] grep: tighten -i doc
* doc/grep.in.1:
* doc/grep.texi (Matching Control):
* src/grep.c (usage):
Make it clearer that -i affects patterns and data, but not
file names (Bug#37604).
---
doc/grep.in.1 | 3 ++-
doc/grep.texi | 3 ++-
src/grep.c | 2 +-
3 files changed, 5 insertions(+), 3 deletions(-)
diff --git a/doc/grep.in.1 b/doc/grep.in.1
index 4a3e274..a2cbf5c 100644
--- a/doc/grep.in.1
+++ b/doc/grep.in.1
@@ -250,7 +250,8 @@ option, search for all patterns given.
The empty file contains zero patterns, and therefore matches nothing.
.TP
.BR \-i ", " \-\^\-ignore\-case
-Ignore case distinctions, so that characters that differ only in case
+Ignore case distinctions in patterns and input data,
+so that characters that differ only in case
match each other.
.TP
.BR \-v ", " \-\^\-invert\-match
diff --git a/doc/grep.texi b/doc/grep.texi
index e6e0dbe..f5edc72 100644
--- a/doc/grep.texi
+++ b/doc/grep.texi
@@ -198,7 +198,8 @@ The empty file contains zero patterns, and therefore matches nothing.
@opindex -y
@opindex --ignore-case
@cindex case insensitive search
-Ignore case distinctions, so that characters that differ only in case
+Ignore case distinctions in patterns and input data,
+so that characters that differ only in case
match each other. Although this is straightforward when letters
differ in case only via lowercase-uppercase pairs, the behavior is
unspecified in other situations. For example, uppercase ``S'' has an
diff --git a/src/grep.c b/src/grep.c
index ef6abb8..4b6b465 100644
--- a/src/grep.c
+++ b/src/grep.c
@@ -1926,7 +1926,7 @@ Pattern selection and interpretation:\n"), getprogname ());
printf (_("\
-e, --regexp=PATTERNS use PATTERNS for matching\n\
-f, --file=FILE take PATTERNS from FILE\n\
- -i, --ignore-case ignore case distinctions\n\
+ -i, --ignore-case ignore case distinctions in patterns and data\n\
-w, --word-regexp match only whole words\n\
-x, --line-regexp match only whole lines\n\
-z, --null-data a data line ends in 0 byte, not newline\n"));
--
2.21.0
