On: /var/tmp/xmas.txt, each unix cmd could only be used once

[cduan]

In some shells (such as tcsh) it is a built-in command like "if" or "cd".

[andrewcooke → cduan]

yeah, i wondered about that (in bash it's /bin/echo, fwiw - i looked).

[thwarted → andrewcooke]

Huh? /bin/echo is an executable, all shells should invoke that binary when given a path to it. In bash, echo is a builtin (it appears in the SHELL BUILTIN COMMANDS section of the man page between disown and enable).

  bash$ echo --help # the builtin
  --help
  bash$ /bin/echo --help # the executable
  Usage: /bin/echo [SHORT-OPTION]... [STRING]...
    or:  /bin/echo LONG-OPTION
  Echo the STRING(s) to standard output.
  (and a bunch of other GNU help text)

[andrewcooke → thwarted]

ah, ok. that makes sense. i just did "which echo" without thinking enough....

[tome → andrewcooke]

Try "type echo".

If "which" is not a builtin (which it isn't in bash, but is in zsh) then it can't tell you about builtins!