(标*号的可选掌握，其他为必须掌握)
一、File management:
ls - list file
touch - create a null file/modify file timestamp
cp/mv/rm/ln - copy/rename/move/delete file, create link
chmod/*chown/*chgrp - change file permission/owner/group
find - search file by name, size, permission, etc.
file - display file type, text, binary, etc.
cp/scp/*rcp - copy/remote copy/secure copy
mkdir/rmdir - create/delete directory
df/du - check disk space/directory space
which - locate a command
zip/unzip/*gzip/*gunzip/ - compress/decompress
*tar - archive processing
二、File content processing:
vi - word edit
wc - word count
tee - replicate the standard output
more/less/pg - page the file to display on the screen
grep/*egrep/*cgrep - filter specific lines from input
diff/*sdiff/*vimdiff - diff files
head/tail - print specific lines of input
cat/split - concatenate files/split a file
*cut/paste - cut specific fields/concatenate line by line
*sort/uniq - sort line by line/remove continuous unique lines
*sed/awk - stream editor/text processing
三、Process/Job management:
top - list the processes that occupy most CPU
jobs - list background jobs
fg/bg - put a job to foreground/background
ps - list the processes
kill/pkill - send signal to a process/processes
*crontab - schedule a task on time of day/day of week
四、Other commands:
echo -
export - set the environmental variables
telnet/ssh/*rlogin - remote shell by telnet/rlogin/ssh
ftp/sftp - ftp/ftp over ssh
sleep - wait for some time
passwd - change password
tcpdump - dump the message over eth
*mailx - send mail
*expect - a utility to automate interactive commands
五、flow control:
for
while
if then else endif