SC3026 – ShellCheck Wiki

See this page on GitHub


In POSIX sh, ^ in place of ! in glob bracket expressions is undefined.

Problematic code:

echo foo-[^0]*.jpg

Correct code:

echo foo-[!0]*.jpg

or if the intention is to match ^ literally then either do not put it immediately after [ or quote it by backslash \

echo foo-[0^]*.jpg foo-[\^0]*.jpg


[^c] is frequently used in most regular expression variants to mean "any character except c". Ksh and Bash adopted it for globs as well.

However, strictly speaking, the only range complement syntax guaranteed to be supported across shells is [!c]. POSIX explicitly states that behavior of [^c] is unspecified. Dash used to support [^c] when compiled with fnmatch and glob from glibc, but it was considered as a bug and fixed in version 0.5.12. Busybox has a similar bug 14516.

In zsh interactive sessions echo foo-[!0]*.jpg may cause zsh: event not found: 0 error due to attempt of history expansion. BASH however suppresses history expansion when ! is first character in square brackets.

Discrepancy of negation syntax in regular expressions and shell pattern matching appeared in early UNIX versions. Pipeline syntax in shells had not settled yet, some terminals had no | key, so ^ was used there. That is why in some shells exclamation mark ! was chosen instead of circumflex (caret) ^ symbol for negation in globs. For more details related to shell history see "The ^ = | ?" thread in the Unix Heritage Society mailing list or Sven Mascheck. The Traditional Bourne Shell Family. History and Development page.


If you only intend to target shells that supports this feature, you can change the shebang to a shell that guarantees support, or ignore this warning. Or just rewrite it to be on the technically correct side.

ShellCheck is a static analysis tool for shell scripts. This page is part of its documentation.