Save this below as listcommands.sh and execute. You should get a file called list-commands.txt with all commands, about 150 k big. I copied the script from somewhere here, it is not my work but i don't know whom to credit for it.
#!/bin/sh
touch /root/list-commands.txt
echo "********************" >> /root/list-commands.txt
echo "Commands in /usr/bin" >> /root/list-commands.txt
echo "********************" >> /root/list-commands.txt
echo "" >> /root/list-commands.txt
ls /usr/bin | xargs whatis >> /root/list-commands.txt
echo "" >> /root/list-commands.txt
echo "********************" >> /root/list-commands.txt
echo "Commands in /usr/sbin" >> /root/list-commands.txt
echo "********************" >> /root/list-commands.txt
echo "" >> /root/list-commands.txt
ls /usr/sbin | xargs whatis >> /root/list-commands.txt
echo "" >> /root/list-commands.txt
echo "********************" >> /root/list-commands.txt
echo "Commands in /bin" >> /root/list-commands.txt
echo "********************" >> /root/list-commands.txt
echo "" >> /root/list-commands.txt
ls /bin | xargs whatis >> /root/list-commands.txt
echo "" >> /root/list-commands.txt
echo "********************" >> /root/list-commands.txt
echo "Commands in /sbin" >> /root/list-commands.txt
echo "********************" >> /root/list-commands.txt
echo "" >> /root/list-commands.txt
ls /sbin | xargs whatis >> /root/list-commands.txt
echo "" >> /root/list-commands.txt