mjhjmtu

I need to perform case-insensitive match with the grepdiff tool. Unlike grep it doesn't have an argument for that, but it has --extended-regexp. Is it possible?

I tried perl-like, but it doesn't work

$ echo SOME | egrep '(?i)some'
$ echo SOME | grepdiff --extended-regexp '(?i)some'
grepdiff: repetition-operator operand invalid

You need to tell the grep family to use Perl-like REs.

echo SOME | grep -P '(?i)some'
SOME

Unfortunately this flag is not available in grepdiff and, as far as I can see, neither is -i (case insensitive match).

Here is a small script, which I've called pgrepdiff, which will allow you to use a PCRE to match your diff output. It does not accept any of the flags that grepdiff allows. It reads from named files or stdin if none is provided. Omitting the RE turns it into an expensive cat operator:

#!/bin/bash
#
# Usage: pgrepdiff <re> [<files...>]
#
# https://unix.stackexchange.com/a/424566/100397
#
tmpd=$(mktemp --tmpdir --directory 'pgd.XXXXXXXXXX')

re="$1"
shift

# Split the file into its context diff parts
cat "$@" | csplit - -f "$tmpd/xx." -k -n4 -s -z '/^@@/' '*'

# Save the header preamble for a match
mv -f "$tmpd/xx.0000" "$tmpd/head"
head=

# Iterate across all the diff segments
shopt -s nullglob
for xx in "$tmpd"/xx.????
do
 if grep -q -P "$re" "$xx"
 then
 [[ -z $head ]] && cat "$tmpd/head" && head=yes
 cat "$xx"
 fi
done

# Tidy up
rm -rf "$tmpd"

# Return 0 (success) iff we matched something
[[ -n $head ]]