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Comment by cferr | Hacker News Reader

Another way to touch a file:

cp /dev/null file

Test if a port is listening without telnet:

echo > /dev/tcp/address/port && echo Yes || echo No

That's not actually a file. It's just a path Bash recognizes and is the interface to socket functionality. udp works too.

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> Another way to touch a file: cp /dev/null file

That destroys a file, making it 0 bytes. It doesn't touch a file, not at all.

And if "file" is the name of an existing directory, it creates an empty file called "file/null".

"touch" exists for a reason.

If the file does not exist, it creates an empty file. That is what most people use touch for.

That's one use case.

The actual use case touch was designed for was to update the timestamp of a file. This is a huge case for developers, since timestamps are used in dependency resolution of partial compilation. [1]

[1] https://man7.org/linux/man-pages/man1/touch.1.html

  NAME
       touch - change file timestamps
  DESCRIPTION
       Update the access and modification times of each FILE to the
       current time.

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