Bash "diff" utility showing files as different when using a regex Ignore

I'm trying to use the bash utility "diff" that is documented here: http://ss64.com/bash/diff.html. Note that I'm using a windows-ported version of the bash utility, but that shouldn't make any difference.

I have two files, regex_test_1.txt and regex_test_2.txt that have the following contents:

regex_test_1.txt:

// $Id: some random id string $ more text

text that matches

regex_test_2.txt:

// $Id: some more random id string $ more text

text that matches

I am trying to diff these files while ignoring any 开发者_如何学Golines that fit this regex:

.*\$(Id|Header|Date|DateTime|Change|File|Revision|Author):.*\$.*

However, when I run diff and tell it to ignore lines matching this regex using the -I argument, this is the output:

C:\Users\myname\Documents>diff -q -r -I ".*\$(Id|Header|Date|DateTime|Change|File|Revision|Author):.*\$.*" regex_test_1.txt regex_test_2.txt
Files regex_test_1.txt and regex_test_2.txt differ

I expect that it should find no differences (and report nothing). Why is it finding these files to be different?

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It's because diff uses basic regex syntax, wherein certain regex metacharacters lose their special meaning:

In basic regular expressions the meta-characters ?, +, {, |, (, and ) lose their special meaning; instead use the backslashed versions \?, \+, \{, \|, \(, and \).

This should work:

.*\$\(Id\|Header\|Date\|DateTime\|Change\|File\|Revision\|Author\):.*\$.*

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Just for giggles, add -b to your diff. Ignore differences in white space.