Bash – the last argument of the previous command

bash

$_ is said to be the last argument of the previous command.

So I wonder why it is not EDITOR="emacs -nw" but EDITOR in the following example?

Why isn't "emacs -nw" part of the last argument?

More generally, what are the definitions of an argument, and the last argument?

Thanks.

$ export EDITOR="emacs -nw"
$ echo $_
EDITOR

Best Answer

Bash processes variable assignments, when they’re allowed as arguments (with alias, declare, export, local, readonly, and typeset), before anything else (or rather, it identifies them before anything else — expansion applies to the values assigned to variables). When it gets to word expansion, the remaining command is export EDITOR, so _ is set to EDITOR.

Generally speaking, arguments are the “words” remaining after expansion (which doesn’t include variable assignments and redirections).

See Simple command expansion in the Bash manual for details.

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Bash Command – Printing and Saving the Last Bash Input Command

You can access the just-executed command line with the history built-in. (I have no idea why history 1 prints the just-executed command line but fc -nl -1 prints the previous commmand, as does fc -nl 0.)

PROMPT_COMMAND='echo -en "\033[38;5;2m"; history 1; echo -en "\033[0m\n"'

This prints a number before the command text. Here's a version that removes the number. (It may be incorrect if you go beyond 99999 history lines, I don't know how bash formats the number then.)

prompt_function () {
  local prompt_history="$(history 1)"
  prompt_history=${prompt_history:7}
  echo -En $'\033[38;5;2m'"$prompt_history"$'\033[0m\n'
}
PROMPT_COMMAND=prompt_function

(Note that echo -en ..."$prompt_history"... would expand backslashes in the command line, so I use echo -E and let the shell expansion generate the control characters with $''.).

Bash – Shell: How to get the last argument the previous command when it was detached

\e-\e. (or pressing - and . while holding alt/option) inserts the second last word.

Similarly, \e-2\e. inserts the third last word, and \e2\e. inserts the third word.

Best Answer

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Bash Command – Printing and Saving the Last Bash Input Command

Bash – Shell: How to get the last argument the previous command when it was detached

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