export

$ export
AWS_HOME=/Users/adnanadnan/.aws
LANG=en_US.UTF-8
LC_CTYPE=en_US.UTF-8
LESS=-R

$ echo $AWS_HOME
/Users/adnanadnan/.aws

whatis something

$ whatis bash
bash (1)             - GNU Bourne-Again SHell

whereis name

$ whereis php
/usr/bin/php

which program_name

$ which php
/c/xampp/php/php

cat filename
cat file1 file2 
cat file1 file2 > newcombinedfile
cat < file1 > file2 #copy file1 to file2

chmod -options filename

chown -options user:group filename

cp filename1 filename2

diff filename1 filename2

file filename

$ file index.html
 index.html: HTML document, ASCII text

find directory options pattern

$ find . -name README.md
$ find /home/user1 -name '*.png'

gunzip filename

gzcat filename

gzip filename

head filename

lpq

$ lpq
Rank    Owner   Job     File(s)                         Total Size
active  adnanad 59      demo                            399360 bytes
1st     adnanad 60      (stdin)                         0 bytes

lpr filename

lprm jobnumber

ls option

more filename

mv filename1 filename2

mv old_name new_name

rm filename

tail filename

touch filename

$ touch trick.md

awk '/search_pattern/ { action_to_take_if_pattern_matches; }' file_to_parse

awk -F':' '{ print $1 }' /etc/passwd

red riding hood went to the park to play

cut -d " " -f2,7,9 example.txt

riding park play

echo Hello World

Hello World

echo -ne "Hello\nWorld\n"

Hello
World

Lorem ipsum
dolor sit amet, 
consetetur
sadipscing elitr,
sed diam nonumy
eirmod tempor
invidunt ut labore
et dolore magna
aliquyam erat, sed
diam voluptua. At
vero eos et
accusam et justo
duo dolores et ea
rebum. Stet clita
kasd gubergren,
no sea takimata
sanctus est Lorem
ipsum dolor sit
amet.

egrep '(Lorem|dolor)' example.txt
or
grep -E '(Lorem|dolor)' example.txt

Lorem ipsum
dolor sit amet,
et dolore magna
duo dolores et ea
sanctus est Lorem
ipsum dolor sit

Lorem ipsum
dolor sit amet,
consetetur
sadipscing elitr,
sed diam nonumy
eirmod tempor
foo (Lorem|dolor) 
invidunt ut labore
et dolore magna
aliquyam erat, sed
diam voluptua. At
vero eos et
accusam et justo
duo dolores et ea
rebum. Stet clita
kasd gubergren,
no sea takimata
sanctus est Lorem
ipsum dolor sit
amet.

fgrep '(Lorem|dolor)' example.txt
or
grep -F '(Lorem|dolor)' example.txt

foo (Lorem|dolor)

Lorem ipsum dolor sit amet, consetetur sadipscing elitr, sed diam nonumy eirmod tempor invidunt ut labore et dolore magna aliquyam erat, sed diam voluptua. At vero eos et accusam et justo duo dolores et ea rebum. Stet clita kasd gubergren, no sea takimata sanctus est Lorem ipsum dolor sit amet.

cat example.txt | fmt -w 20

Lorem ipsum
dolor sit amet,
consetetur
sadipscing elitr,
sed diam nonumy
eirmod tempor
invidunt ut labore
et dolore magna
aliquyam erat, sed
diam voluptua. At
vero eos et
accusam et justo
duo dolores et ea
rebum. Stet clita
kasd gubergren,
no sea takimata
sanctus est Lorem
ipsum dolor sit
amet.

grep pattern  filename

$ grep admin /etc/passwd
_kadmin_admin:*:218:-2:Kerberos Admin Service:/var/empty:/usr/bin/false
_kadmin_changepw:*:219:-2:Kerberos Change Password Service:/var/empty:/usr/bin/false
_krb_kadmin:*:231:-2:Open Directory Kerberos Admin Service:/var/empty:/usr/bin/false

$ grep -r admin /etc/

Lorem ipsum
dolor sit amet,
consetetur
sadipscing elitr,
sed diam nonumy
eirmod tempor
invidunt ut labore
et dolore magna
aliquyam erat, sed
diam voluptua. At
vero eos et
accusam et justo
duo dolores et ea
rebum. Stet clita
kasd gubergren,
no sea takimata
sanctus est Lorem
ipsum dolor sit
amet.

nl -s". " example.txt

1. Lorem ipsum
     2. dolor sit amet,
     3. consetetur
     4. sadipscing elitr,
     5. sed diam nonumy
     6. eirmod tempor
     7. invidunt ut labore
     8. et dolore magna
     9. aliquyam erat, sed
    10. diam voluptua. At
    11. vero eos et
    12. accusam et justo
    13. duo dolores et ea
    14. rebum. Stet clita
    15. kasd gubergren,
    16. no sea takimata
    17. sanctus est Lorem
    18. ipsum dolor sit
    19. amet.

Hello This is a Test 1 2 3 4

sed 's/ /-/g' example.txt

Hello-This-is-a-Test-1-2-3-4

sed 's/[0-9]/d/g' example.txt

Hello This is a Test d d d d

f
b
c
g
a
e
d

sort example.txt

a
b
c
d
e
f
g

sort example.txt | sort -R

b
f
a
c
d
g
e

Hello World Foo Bar Baz!

cat example.txt | tr 'a-z' 'A-Z'

HELLO WORLD FOO BAR BAZ!

cat example.txt | tr ' ' '\n'

Hello
World
Foo
Bar
Baz!

a
a
b
a
b
c
d
c

sort example.txt | uniq

a
b
c
d

sort example.txt | uniq -c

3 a
    2 b
    2 c
    1 d

wc filename

$ wc demo.txt
7459   15915  398400 demo.txt

$ cd

cd dirname

mkdir dirname

pwd

dig domain

du [option] [filename|directory]

du -sh pictures
1.4M pictures

finger username

last yourUsername

man command

ping host

ps -u yourusername

quota -v

scp source_file user@host:directory/target_file

scp user@host:directory/source_file target_file
scp -r user@host:directory/source_folder target_folder

scp -P port user@host:directory/source_file target_file

ssh user@host

ssh -p port user@host

uname -a

wget file

whois domain

kill PID

killall processname

command &

nohup command

nohup command &

#!/bin/bash

str="hello world"

echo $str   # hello world

array[0] = val
array[1] = val
array[2] = val
array=([2]=val [0]=val [1]=val)
array=(val val val)

${array[i]}     # i是数组下标

${#array[@]}

${varname:-word}    # 如果 varname 存在而且不为 null，返回它的值，否则返回 word
${varname:=word}    # 如果 varname 存在而且不为 null，返回它的值，否则把word赋值给它并且返回 word
${varname:+word}    # 如果 varname 存在而且不为 null，返回 word，否则返回 null
${varname:offset:length}    # 它返回 $varname 的子字符串，从 offset 处开始，长度为 length

${variable#pattern}         # 如果 pattern 匹配变量值的起始部分，删除匹配 pattern 的最短的部分，然后返回剩余的
${variable##pattern}        # 如果 pattern 匹配变量值的起始部分，删除匹配 pattern 的最长的部分，然后返回剩余的
${variable%pattern}         # 如果 pattern 匹配变量值的结束部分，删除匹配 pattern 的最短的部分，然后返回剩余的
${variable%%pattern}        # 如果 pattern 匹配变量值的结束部分，删除匹配 pattern 的最长的部分，然后返回剩余的
${variable/pattern/string}  # 把变量值中匹配 pattern 的最长的部分替换为 string，只替换第一个匹配的部分
${variable//pattern/string} # 把变量值中匹配 pattern 的最长的部分替换为 string，全局进行替换
${#varname}     # 返回变量值作为一个字符串的长度

function name() {
    shell commands
}

#!/bin/bash
function hello {
   echo world!
}
hello

function say {
    echo $1
}
say "hello world!"

if [expression]; then
    will execute only if expression is true
else
    will execute if expression is false
fi

case expression in
    pattern1 )
        statements ;;
    pattern2 )
        statements ;;
    ...
esac

statement1 && statement2  # 两个语句都为真
statement1 || statement2  # 至少一个语句为真

str1=str2       # str1 匹配 str2
str1!=str2      # str1 不匹配 str2
str1<str2       # str1 小于 str2
str1>str2       # str1 大于 str2
-n str1         # str1 不是 null (长度大于 0)
-z str1         # str1 是 null (长度为 0)

-a file         # 文件存在
-d file         # 文件存在而且是目录
-e file         # 文件存在，跟 -a 一样
-f file         # 文件存在，而且是常规文件（不是目录或者其他特殊类型的文件）
-r file         # 你有读权限
-s file         # 文件存在而且不为空
-w file         # 你有写权限
-x file         # 你对文件有执行权限，如果 file 是目录的话，你对它有搜索权限
-N file         # 从上次读之后文件被修改过
-O file         # 你是文件所有者
-G file         # 文件的 group ID 跟你的 group ID （或之一，如果你在很多分组里）相同

file1 -nt file2     # file1 比 file2 更新
file1 -ot file2     # file1 比 file2 更老

-lt     # 小于
-le     # 小于等于
-eq     # 等于
-ge     # 大于等于
-gt     # 大于
-ne     # 不等于

for x := 1 to 10 do
begin
  statements
end

for name [in list]
do
  statements that can use $name
done

for (( initialisation ; ending condition ; update ))
do
  statements...
done

while condition; do
  statements
done

until condition; do
  statements
done

source ~/.bashrc
cd $hotellogs

function finish {
  # 在这里执行清理语句，例如，杀掉所有 fork 的进程。
  jobs -p | xargs kill
}
trap finish EXIT

echo export FOO=BAR >> ~/.bash_profile

# 如果用户的私有 bin 目录存在的话，把它添加到 PATH 变量中
    if [ -d "$HOME/bin" ] ; then
        PATH="$HOME/bin:$PATH"
    fi

bash -n scriptname
bash -v scriptname
bash -x scriptname