export

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

$ echo $SHELL
/usr/bin/zsh

whereis name

$ whereis php
/usr/bin/php

which program_name 

$ which php
/c/xampp/php/php

ls option

touch filename

$ touch trick.md

cat filename
cat file1 file2 
cat file1 file2 > newcombinedfile

more filename

head filename

tail filename

mv filename1 filename2

cp filename1 filename2

rm filename

diff filename1 filename2

chmod -options filename

gzip filename

gunzip filename

gzcat filename

lpr filename

lpq

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

lprm jobnumber

awk ‘/search_pattern/ { action_to_take_if_pattern_matches; }‘ file_to_parse

awk -F‘:‘ ‘{ print $1 }‘ /etc/passwd

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/

wc filename

$ wc demo.txt
7459   15915  398400 demo.txt

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

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

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.

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.

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!

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.

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) 

mkdir dirname

$ cd

cd dirname

pwd

ssh user@host

ssh -p port user@host

quota -v

finger username

uname -a

man command

du filename

last yourUsername

ps -u yourusername

kill PID

killall processname

ping host

whois domain

dig domain

wget file

scp source_file user@host:directory/target_file

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

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

#!/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]}     # where i is the index

${#array[@]}

${varname:-word}    # 如果varname存在且不为null，则返回其值; 否则返回word
${varname:=word}    # 如果varname存在且不为null，则返回其值;否则设置它，然后返回其值
${varname:+word}    # 如果varname存在并且不为null，返回word; 否则返回null 
${varname:offset:length}    # 执行子字符串扩展。它返回$ varname的子字符串，从offset开始，最多为length的字符

${variable#pattern}         # if the pattern matches the beginning of the variable‘s value, delete the shortest part that matches and return the rest
${variable##pattern}        # if the pattern matches the beginning of the variable‘s value, delete the longest part that matches and return the rest
${variable%pattern}         # if the pattern matches the end of the variable‘s value, delete the shortest part that matches and return the rest
${variable%%pattern}        # if the pattern matches the end of the variable‘s value, delete the longest part that matches and return the rest
${variable/pattern/string}  # the longest match to pattern in variable is replaced by string. Only the first match is replaced
${variable//pattern/string} # the longest match to pattern in variable is replaced by string. All matches are replaced
${#varname}     # returns the length of the value of the variable as a character string

functname() {
    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  # 两边的条件都为true
statement1 || statement2  # 其中一边为true

str1=str2       # str1 匹配 str2
str1!=str2      # str1 不匹配 str2
str1<str2       # str1 是否小于 str2
str1>str2       # str1 是否大于 str2
-n str1         # str1 不为空(长度大于 0)
-z str1         # str1 为空(长度为 0)

-a file         # 文件存在 
-d file         # 文件存在，是一个目录 
-e file         # 文件存在; 相同的-a 
-f file         # 文件存在，是一个常规文件（即不是目录或其他特殊类型的文件） 
-r file         # 你有读权限 
-r file         # 文件存在，不为空 
-w file         # 你有写权限 
-x file         # 你有文件的执行权限

file1 -nt file2     # file1 is newer than file2
file1 -ot file2     # file1 is older than file2

-lt     # 小于 
-le     # 小于或等于 
-eq     # 等于
-ge     # 大于或等于 
-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

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