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Try executing the following under a bash shell echo "Reboot your instance!"

On my installation:

root@domU-12-31-39-04-11-83:/usr/local/bin# bash --version GNU bash, version 4.1.5(1)-release (i686-pc-linux-gnu) Copyright (C) 2009 Free Software Foundation, Inc. License GPLv3+: GNU GPL version 3 or later <http://gnu.org/licenses/gpl.html> This is free software; you are free to change and redistribute it. There is NO WARRANTY, to the extent permitted by law. root@domU-12-31-39-04-11-83:/usr/local/bin# uname -a Linux domU-12-31-39-04-11-83 2.6.35-22-virtual #35-Ubuntu SMP Sat Oct 16 23:57:40 UTC 2010 i686 GNU/Linux root@domU-12-31-39-04-11-83:/usr/local/bin# echo "Reboot your instance!" -bash: !": event not found

Can anyone please explain what is "bash events?" I've never heard this concept before. Also, how should I output "!" at the end of the sentence?

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10 Answers 10

Reset to default
127

You can turn off history substitution using set +H.

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  • 3
    Do you know the reasoning behind the syntax? It seems really counter intuitative. You'd think you'd type +H to enable something and -H to disable something. Commented May 16, 2016 at 9:19
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    @PunkyGuy: I don't know the history (pun intended) behind it, but Unix options typically start with a hyphen (or minus) and + is simply the opposite of that. Commented May 16, 2016 at 13:19
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    From help set (in bash): "Using + rather than - causes these flags to be turned off." Commented Oct 5, 2020 at 8:41
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    While this question correctly addresses bash, since that's what the question asked, I thought I'd mention that in zsh, the approximate equivalent is set -K or setopt NO_BANG_HIST (capitalization and underscores optional, but that's how it shows up in the docs, so referencing it that way in case folks want further details). Commented Mar 27, 2022 at 23:35
  • This should be an edit to this answer. Edit to add substantial context or new answer Commented Nov 10, 2024 at 10:38
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! is a special character to bash, it is used to refer to previous commands; eg,

!rm

will recall and execute the last command that began with the string "rm", and 

!rm:p

will recall but not execute the last command that began with the string "rm". bash is interpreting the exclamation mark in echo "reboot your instance!" as "substitute here the last command that began with the character(s) immediately following the exclamation mark", and grumbles at you that it cannot find an event (command) in your history that began with a single double-quote.

Try

echo reboot your instance\!

to protect (escape) the exclamation mark from bash.

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    Write two echo statements; you get the linefeed for free. Commented Dec 2, 2010 at 14:22
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    Simple solution is to use single quotes and double quotes at once: echo -e "Text\nReeboot"'!' Commented Oct 2, 2014 at 4:51
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    This sucks. If I don't escape the exclamation mark, bash throws a fit. If I do escape it, the backslash is included in the final string. Why do you do this, Bash!! (pastebin.com/g4PYv56A) Commented Jan 23, 2015 at 7:46
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    @Hubro in fairness, I'm not sure that's all bash's fault. You have somewhat complicated matters by using ruby to feed things to bash, and it's not clear to me what part ruby is playing in the stripping or reinforcing of escape characters. Commented Jan 23, 2015 at 8:25
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    echo 'Reboot your instance!' works as well, as characters in between ' makes the shell interpret them literally. Commented Aug 29, 2020 at 23:27
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To solve your original problem, try using single quotes, rather than double quotes. With the latter, bash will attempt to expand certain characters before passing the result on to the command (echo in this case). With single quotes, bash passes the entire string, unchanged.

! is used in commands to refer to the command line history. See: http://tldp.org/LDP/abs/html/abs-guide.html#HISTCOMMANDS for a full set. With the above example, bash is trying to expand !" as a reference to an event before echo gets a look in, hence the error.

Note that in scripts, all of the history commands are disabled, as they only make sense in an interactive shell.

The only one I use on a regular basis, is !$. It expands to the last argument of the previous command. It's a useful shorthand in places.

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    !! to fill in the complete last command entered is remarkably useful; particularly, sudo !! or pfexec !! Commented Dec 2, 2010 at 11:20
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    I also find sudo and pfexec to be nice utilities, but no need to be so enthusiastic. Commented Apr 17, 2014 at 0:08
  • $_ works in more shells than bash and it's a proper variable, unlike !$. (and @LeartS: I liked your joke's lack of emoticons. ;) ) Commented Jul 23, 2016 at 0:28
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Just put a space between ! and " than it'll work.

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    Could you please add an explanation as to why your solution works? Commented Sep 26, 2014 at 8:20
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    This works because Bash only treats ! as a special character if it's directly followed by a non-whitespace character. However, it will also add an extra blank to your output, so that might not always be desired... Commented Oct 2, 2014 at 4:50
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Yes, ! is a special character to bash, it is used to refer to previous commands.

Few of the ways you can handle the situation

The following will output the string as it is

echo 'Reboot your instance!'

The following will execute the command and concatenate the string

echo 'escaping #'" adding `which python` to the string" echo '#!'`which python`
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You can also add

histchars=

In ./bash_profile (or use it as a once-off on the command line)

To disable ! from being a 'special history char', or to set it to something else.

Warning; some things may break when you set it for example to ~ and possibly other strings.

Look:

$ echo "!test" -bash: !test: event not found $ histchars= $ echo "!test" !test $ histchars=7 $ echo "7test" -bash: 7test: event not found $ histchars= $ histchars=~ $ histchars= hars=hars=~ # odd output $ ~/test -bash: /test: event not found
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You could also use a heredoc:

cat <<EOF Reboot your instance! EOF

It's annoying in this case because it's not a one-liner but for longer commands (like writing a bash script), it works great.

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In bash 4.3 it seems you no longer need to use single quotes or set +H:

$ bash --version GNU bash, version 4.3.46(1)-release (x86_64-unknown-linux-gnu) [...] $ echo "Reboot your instance!" Reboot your instance!
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  • Probably a bug, because here, I have 4.4.12 and yet again, I need set +H or quoting. Or you have set +H somewhere (like in /etc/profile). Commented Apr 2, 2018 at 11:20
  • Using !-char not at the end of the sentence verifies bash's event detection is still working fine. Version is 4.3.30 ........ $ echo "Recheck your sentence!foo" bash: !foo: event not found Commented Aug 4, 2018 at 14:49
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!is special character for zsh. It points to previous command.
If you need to use it as string character, try \!

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    The question was about bash. Commented Nov 9, 2020 at 15:23
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escape it: echo reboot your instance\!

And if you ran into something when you need to use two Exclamations, use: ls *[\!'!']*

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