touch

3 min read

touch does one of two things, depending on whether the file already exists:

• if the file does not exist, touch creates it, empty;
• if the file does exist, touch updates its timestamps to the current time.

touch [options] [file...]

$ touch notes.txt        # create notes.txt if absent, else bump its times

The "create an empty file" behaviour is the everyday use. The "update timestamps" behaviour matters to tools that decide what work to do by comparing file times — touch is how you tell such a tool that a file should be considered freshly changed.

Which timestamps, and to what #

By default touch sets both the access time and the modification time to the current moment. These options narrow or redirect that.

Not creating a file #

To use touch purely to update timestamps, and never to create anything:

Setting a created file's security #

When touch creates a file, that new file needs a security descriptor, and by default it inherits one from the directory it is created in.

touch accepts the shared creation flags — --owner, --group, --label, --no-inherit, and --sddl — to set that descriptor explicitly. They behave exactly as they do for mkdir; the full reference is on the mkdir page.

These flags apply only on the create path. If touch is updating the timestamps of a file that already exists, there is no new descriptor to set, and the creation flags have nothing to do — they do not alter an existing file's security. Pair them with -c and they never take effect at all, since -c means nothing is ever created.

Exit status #

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