How to make shell execute a command prior to every user input command

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.

This smells like an XY problem. What is it you're really trying to accomplish? — Mr. Llama
– Mr. Llama, Commented Apr 21, 2015 at 15:18

Maxim Egorushkin · Accepted Answer · 2015-04-21 13:15:08Z

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.

answered Apr 21, 2015 at 13:15

Maxim Egorushkin

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2 Comments

user3446120 Over a year ago

No i need <my_command>to be executed before shell starts executing the command passed by user. PROMPT_COMMAND is executed by shell after executing the command passed by user. In above case before shell executes "pwd" it should execute "my_command"

Mr. Llama Over a year ago

PROMPT_COMMAND is executed when Bash displays a prompt which is before a user types a command.

Robert Vojcik · Accepted Answer · 2015-04-21 15:13:03Z

0

My example

function preexec() {
  echo "Preexec command"
}

trap 'preexec' DEBUG

Result is

# pwd
Preexec command
/home/robert

answered Apr 21, 2015 at 15:13

Robert Vojcik

1

2 Comments

user3446120 Over a year ago

I'm using this version of shell "GNU bash, version 2.04.0(1)-release",according to the man page of this version PROMPT_COMMAND is executed after User's input is executed.

Robert Vojcik Over a year ago

Sorry, then. I think there is no way how to do it :(

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