如何使Shell在每个用户输入命令之前执行命令

Question

I need a command to be executed before shell starts to execute the user passed command,i tried using trap with DEBUG signal, but that did not happen.

I have registered trap in /etc/profile.

trap 'echo "my_command"' DEBUG

Whats happening now is:

sw0:root:root> pwd

/root

my_command

sw0:root:root>

What i want is:

sw0:root:root> pwd

my_command

/root

sw0:root:root>

Bash Version Used:

GNU bash, version 2.04.0(1)-release (powerpc-unknown-linux-gnu)

I want my command to be executed prior to every command entered by user in shell,how do i do that?

Please help me on this,i tried lot of googling but that does not help.

Answer 1

You are probably looking for something like PROMPT_COMMAND :

The contents of this variable are executed as a regular Bash command just before Bash displays a prompt.

Answer 2

My example

function preexec() {
  echo "Preexec command"
}

trap 'preexec' DEBUG

Result is

# pwd
Preexec command
/home/robert