Many linux distro build nowadays, each distro came with spesific purpose, server, workstation or desktop orientation but still not forget to give access to shell 
people who run “ifconfig” in mandriva will get confuse when run same command in fedora or maybe slackware
“command not found” is common message
just use “whereis” command for this purpose :
whereis ifconfig
whereis perl
whereis sh
answer will show up for full path of program
type full path in shell to get same result, not easy but always work