expr: '$' should act as a special character only at the end of regex or subexpression

[frendsick]

The '$' character should be escaped when it is not used in a spot that makes it act as a special character.

It is the same as ^, but refers to end of pattern space. $ also acts as a special character only at the end of the regular expression or subexpression (that is, before \) or \|), and its use at the end of a subexpression is not portable.

Reference: https://www.gnu.org/software/sed/manual/html_node/BRE-syntax.html

The test test_bre11 is failing because the '$' is not escaped. On the other hand, test_bre13 works almost by accident, because the '$' character is never escaped in the first place. Both of these tests should pass after fixing the interpretation of the '$' character.

[sylvestre]

could you please provide a simple test case demonstrating this issue ? thanks

[frendsick]

I created a PR #7953 that should fix this.

The test_bre11 is a simple test case for a situation where the '$' should be handled literally. The PR un-ignores it.

The test_bre13 is a test case where the '$' should be handled as an end-of-pattern anchor because it is at the end of a capturing group, so it is before \).

Even simpler test case than test_bre13 where the '$' should be handled as its special meaning would be the following (also included by #7953):

    new_ucmd!()
        .args(&["ab", ":", "a\\(b$\\)"])
        .succeeds()
        .stdout_only("b\n");