On 10/25/25 12:52 PM, Maksym Telychko wrote:
Bash Version: 5.2 Patch Level: 37 Release Status: releaseDescription:The backslash escape symbol works inconsistently when unquoted parameter expansion occurs
The problem, if it can be termed one, is that backslash is special to both the shell's token recognition and word expansion, and to pathname expansion. Bash doesn't really attempt to do anything special with unquoted parameter expansions -- the results are simply passed to the globbing functions (or not, if there are no unquoted globbing characters). If the parameter expansion is quoted, bash does its best to prevent the characters that are special to pathname expansion from being treated specially.
Repeat-By:
Say, I have a directory named '\*123' (literally: backslash, asterisk,
one, two, three).
For being more clean, set the shell option `shopt -s nullglob`
Following code produces unexpected results:
pat='\*'
echo $pat
It prints '\*' instead of '\*123'.
Virtually all shells do this (mksh is an outlier here), but they may get there different ways. Bash does it this way:
Looks like backslash works as escape symbol here, but for asterisk only.
The backslash prevents the `*' from being recognized as a pathname expansion character, so the shell never attempts pathname expansion.Other shells may pass the string to pathname expansion, but the backslash will prevent the `*' from having its special meaning.>If you assign `pat='\\'`, it will print '\\' as expected.
Yes. Backslash isn't one of the characters that's special to pathname expansion, so this isn't really relevant.
To get expected result,> you need to assign `pat='\\*'`. I think it's confusing.
Since you're using an unquoted word expansion, you have to prevent the
backslash from quoting the `*'. A backslash quoting the backslash is one
way to do that.
--
``The lyf so short, the craft so long to lerne.'' - Chaucer
``Ars longa, vita brevis'' - Hippocrates
Chet Ramey, UTech, CWRU [email protected] http://tiswww.cwru.edu/~chet/
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