topic Re: Shell command execution in Operating System - Linux

Shell command execution

SGK — Tue, 18 Jul 2006 23:38:27 GMT

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.

Re: Shell command execution

Jeroen Peereboom — Wed, 19 Jul 2006 00:40:54 GMT

L.S.

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

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

JP

Re: Shell command execution

Alexander Chuzhoy — Wed, 19 Jul 2006 00:47:38 GMT

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

Re: Shell command execution

Ivan Ferreira — Wed, 19 Jul 2006 09:00:09 GMT

-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.