The output of `history` shows the long rsync command you need as entry number 512. Which is the shortest way to run exactly that entry again?
LPIC-1 Exam 101-500, objective 103. GNU and Unix commands medium
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The options
Correct !512
Correct. !n is history expansion by absolute event number, so !512 re-runs the command recorded as entry 512.
Not correct !-512
Wrong. A minus sign makes the number relative: !-512 means the command 512 entries back from the current one, which is a different event.
Not correct history 512
Wrong. Given a number, history prints that many of the most recent entries. It displays, it never executes.
Not correct !?512?
Wrong. !?string? finds the most recent command CONTAINING that string, so it would match any command with 512 in its text — a file size, a port number — rather than event 512.
Why
History expansion has event designators and word designators. The event designators are !n for an absolute number, !-n for a relative offset, !! for the previous command, !string for the last command beginning with string, and !?string? for the last command containing it. Word designators such as !$ and !* then pick parts of the chosen event.
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.
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