SC2326 – ShellCheck Wiki

! is not allowed in the middle of pipelines. Use command group as in `cmd | { ! cmd; }` if necessary.

Problematic code:

cat | ! tee /dev/full

Correct code:

Either negate the entire pipeline (this is equivalent unless pipefail is set):

! cat | tee /dev/full

Or use a command group to negate a single stage:

cat | { ! tee /dev/full; }

Rationale:

POSIX specifies that a status negation operator ! is only used to negate the status of an entire pipeline, not individual stages.

By default the status of a pipeline is that of the last command, so use ! in front of the pipeline to negate as necessary.

If you have set the option pipefail to OR the status of each stage together, and want to negate the status of only a single stage, you can use negate inside a { ! command group; }.

Exceptions:

Ksh supports ! in front of individual pipeline stages. ShellCheck does not warn when the shebang declares that the script will run with Ksh.

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