Apache Introduction & Apache Shell Commands Print

Following are some of the commands that will help you know the apache which is already installed on your system:
which httpd, tells where is http executable is located. 
whereis httpd, gives path of http executable with config path. 
httpd -v, shows version of apache installed in your system.
httpd -t -D DUMP_MODULES, shows all modules loaded with apache. 
httpd -t -D DUMP_VHOSTS , lists all vhosts[virtual hostnames] from apache config file.
httpd -t, shows if your apache config syntax is good or not.

Usage:  httpd [-D name] [-d directory] [-f file]
                                   [-C "directive"] [-c "directive"]
                                   [-k start|restart|graceful|graceful-stop|stop]
                                   [-v] [-V] [-h] [-l] [-L] [-t] [-T] [-S]
Options:
  -D name            : define a name for use in  directives
  -d directory       : specify an alternate initial ServerRoot
  -f file            : specify an alternate ServerConfigFile
  -C "directive"     : process directive before reading config files
  -c "directive"     : process directive after reading config files
  -e level           : show startup errors of level (see LogLevel)
  -E file            : log startup errors to file
  -v                 : show version number
  -V                 : show compile settings
  -h                 : list available command line options (this page)
  -l                 : list compiled in modules
  -L                 : list available configuration directives
  -G                : list available configuration directives after loading conf file
  -t -D DUMP_VHOSTS  : show parsed settings (currently only vhost settings)
  -S                 : a synonym for -t -D DUMP_VHOSTS
  -t -D DUMP_MODULES : show all loaded modules
  -M                 : a synonym for -t -D DUMP_MODULES
  -t                 : run syntax check for config files
  -T                 : start without DocumentRoot(s) check