Failglob

Failglob is a shell option available in the Bash shell that affects pathname expansion, or globbing. When failglob is enabled, a glob pattern that does not match any files or directories triggers an error rather than being left unexpanded or behaving unpredictably. The result is typically a non-zero exit status and an error message such as “No match.”

In practice, failglob changes how commands behave when globs fail to find matches. If a pattern like *.txt is used in a command and there are no files matching it, Bash will report an error instead of passing the pattern through or expanding it to an empty result. If the glob does have matches, the expansion proceeds normally and the command runs as usual. The option is designed to help catch mistakes in scripts and command lines by ensuring that missing files are reported immediately.

Enabling and configuring failglob is done in Bash using set -o failglob or by using shopt -s failglob in interactive sessions. This makes the behavior explicit and consistent across commands that rely on pathname expansion. Because failglob is a Bash-specific feature, its availability and exact behavior may differ in other shells, which may implement their own mechanisms for handling unmatched globs.

Examples illustrate the difference: with matches, a command such as echo *.c expands to the list of .c files; with failglob and no matches, Bash reports an error rather than echoing the literal pattern. This option is commonly used in scripts where strict file presence is required and unexpected missing files should halt execution.