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I guess it's equivalent to `: <file` i.e. hooking up the stdin of the no-op command.

• xigoi 3y ago
  Doesn't seem to be the case. For example, `< file cat` shows the file, whereas `: < file cat` or `: < file | cat` does nothing.
  • frou_dh 3y ago
    Not sure what's surprising you in those snippets. `:` itself is a command and it does nothing with its arguments or stdin. https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V3_chap02.html#tag_18_16 https://pubs.opengroup.org/onlinepubs/9699919799/utilities/V...
    • xigoi 3y ago
      I know. The only thing surprising me is your previous claim that `< file` is equivalent to `: < file`.
      • frou_dh 3y ago
        My interpretation of sgarland's question was that he meant `<file` being the entirety of the statement, i.e. typing only that at a shell prompt and pressing return.
        • xigoi 3y ago
          Ah. Now I understand where the misunderstanding was. It confused me that we were talking about redirection as a replacement for useless use of cat.
          • frou_dh 3y ago
            Yep I can appreciate the misunderstanding. For completeness of the discussion, I think where sgarland mentioned a sub-shell, he was possibly referencing the Bashism `$(<` detailed on this page https://www.gnu.org/software/bash/manual/html_node/Command-Substitution.html https://www.gnu.org/software/bash/manual/html_node/Command-S... in addition to what I called a "statement" above.
            • sgarland 3y ago
              Correct, that’s what I had in mind.