You have run a long sequence of commands in one terminal and want them written to ~/.bash_history right now, so a second terminal can read them, without closing the session and without discarding the history the file already holds. Which command does that?
LPIC-1 Exam 101-500, objective 103. GNU and Unix commands hard
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How these questions are written — where each question comes from, what the verification ledger records, and what happens when one is found wrong.
The options
Correct history -a
Correct. -a appends the lines entered in this session since the last append to the history file, leaving everything already in the file untouched.
Not correct history -w
Wrong here. -w writes the whole current in-memory list OVER the history file. Anything another session appended in the meantime is lost.
Not correct history -r
Wrong, and the opposite direction. -r reads the contents of the history file into the current session's list.
Not correct history -c
Wrong, and destructive. -c clears the in-memory history list; if the shell then writes it out, the record of the session goes with it.
Why
The history builtin moves lines between the in-memory list and the file named by HISTFILE: -a appends new lines, -w overwrites the file with the whole list, -r reads the file in, -n reads only the lines not already read. Normally the shell appends on exit, so nothing reaches the file mid-session. Setting PROMPT_COMMAND='history -a' is the usual way to make that happen after every prompt.
Where this comes from
- Cited
- manual page bash(1)
Practise this
Reading one question is not practice. The trainer will draw a short set from objective 103 and space the ones you get wrong.
More questions on this objective
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