Linux – grep results are different when using the –color=always option

grep results are different when using the –color=always option… here is a solution to the problem.

grep results are different when using the –color=always option

I’m having this issue with grep and wondering if it’s a bug. A reproducible scenario is a file that contains the following:


and save it as “file”. The goal is to use grep with –color=always to output “string” while excluding “string-“. Without –color, the following will work as expected:

$ grep string file | grep -v string-

But use –color to output two instances:

$ grep --color=always string file | grep -v string-

I tried several variants, but it seems that –-color breaks the expected behavior. Is this a mistake or am I misunderstanding something? My assumption is that passing --color should have no effect on the result.


@Jake Gould’s answer provides a good analysis of what actually happened, but let me try to put it in a different way:

--color=always Use ANSI escape codes for coloring.

In other words: --color=always changes its output by design, because it must add the necessary escape sequences to achieve coloring.

Never use –-color=always unless you know that the output is expected to contain ANSI escape sequences – typically, for the human eyeball on the terminal.

If you’re not sure how the input will be handled, use --color=auto, which I believe causes grep to apply shading only when its standard output is connected to the terminal.

In a given pipeline, it usually only makes sense to apply –color=auto (or –-color=always) to the grep command, which is the last command in the pipeline.

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