Can i use one .htaccess file for different folders on Linux server

Try this:

#####
SetEnvIf Request_URI ^/admin1 auth=1
SetEnvIf Request_URI ^/admin2 auth=1
SetEnvIf Request_URI ^/admin3 auth=1

AuthName "Please login"
AuthType Basic
AuthUserFile /path_to_file_which_contains_user_login_pwd/.htpasswd

## first, allow everybody
Order Allow,Deny
Satisfy any
Allow from all
Require valid-user
# then, deny only if required
Deny from env=auth
#####

Yes, there are two options.

Option 1)
Have similar, or the same .htaccess files in every directory you wish to protect, which reference a single .htpassword file:

AuthUserFile /etc/httpd/.htpasswd
AuthName "Some Secret FIles"
AuthType Basic
require valid-user

Option 2) Symlink a single .htaccess file into every directory (This means if you change anything in your master .htaccess file all the symlinks will be updated

Instead of putting the same file in all the different folders, you could restrict access to a common parent folder instead. E. g. like this:

/parent            <-- this folder is protected by .htaccess
/parent/admin1
/parent/admin2
/parent/admin3

This way you would only have to maintain a single .htaccess file.

A different would be linking the same .htaccess file into all three folders using symlinks (if you are on a *nix based OS / on Windows you might use junctions when on NTFS). But I am not sure if Apache allows symlinks as .htaccess files

Short Answer is Yes you can use same .htaccess file.

This is how HTTP Authentication works. You can just copy same .htaccess to all three folders and the user will be able to browse all three folders with out being asked for password again. The authentication basically depend on the password file, as far as the password file is same the rest doesn't matter. It will work everywhere on your domain. So you can use the same .htaccess file.