Shell command execution

[SGK]

Hi,

The following command is not working:

[root@localhost tmp]# a=`echo Hello!`
-bash: !`: event not found

The document says "exclamation mark" triggers the Bash "history mechanism."

Can someone explain in detail?

TIA.

[Jeroen Peereboom]

L.S.

try
a='Hello!
or a=`echo "$SomeVar"'Hello!'`

The single quotes form a literal string.
Check bash man page for QUOTING.

JP

[Alexander Chuzhoy]

You must prepend the exclamation mark with a backslash
the following will work:
a=`echo Hello\!`

[Ivan Ferreira · Accepted solution]

-bash: !`: event not found

You get this error because in the bash shell if you run !something, the shell tries to find the last command that starts the word "something", that is, the ! is a special character for bash.

For example:

ls /usr/share/doc
echo "Hello"
!ls

The last command will run ls /usr/share/doc again.