Why does `!45` get replaced with `top`?

Question

I was trying to a string search within Ubuntu 12.04 which went as follows:

find . -exec grep -l "!45" {} \;

Instead of searching for the string "!45", it was replaced with top. It didn't invoke the commmand, but merely start searching for the term "top". Until I figured out -F for grep, I thought special characters would be treated as text in between quotations.

Anywho, now that I've discovered this, I have no idea what this is, what it's used for, or why it even exists!

If you truly don't want ! style history control, turn it off in your ~/.bashrc: set +H or set +o histexpand — glenn jackman, Jul 16 '13 at 20:06

score 9 · Accepted Answer · answered Jul 16 '13 at 19:38

9

In the bash shell, !45 returns that command from the command history (or !32 or !873).

An event designator is a reference to a command line entry in the history list. Unless the reference is absolute, events are relative to the current position in the history list.

!

Start a history substitution, except when followed by a space, tab, the end of the line, ‘=’ or ‘(’ (when the extglob shell option is enabled using the shopt builtin).

!n

Refer to command line n.

Check here for full details from the bash manual.

answered Jul 16 '13 at 19:38

EightBitTony

21,373

Ya know... I never thought about maning bash. +1 for the idea and hopefully not getting caught up in shell related scenarios like this one in the futur. – Chad Harrison Jul 16 '13 at 19:42
2

Been using bash for years, and never knew about that expansion - so we both learned something useful today! Which is why I love answering questions on StackExchange. – EightBitTony Jul 16 '13 at 19:48
2

@hydroparadise: In your defense, the bash man page is enormous. – Aesin Jul 16 '13 at 22:51
@aesin and searching for '!' isn't that easy :) – EightBitTony Jul 17 '13 at 06:17

Why does `!45` get replaced with `top`?

1 Answers1