if command
then
truecommands
fi

wsx@wsx-ubuntu:~/script_learn$ cat test1.sh
#! /bin/bash
# testing the if statement
if pwd
then
    echo "It worked"
fi

wsx@wsx-ubuntu:~/script_learn$ chmod u+x test1.sh
wsx@wsx-ubuntu:~/script_learn$ ./test1.sh
/home/wsx/script_learn
It worked

if command; then
commands
fi

wsx@wsx-ubuntu:~/script_learn$ cat test3.sh
#!/bin/bash
# testing multiple commands in the then section
#
testuser=wsx
#
if grep $testuser /etc/passwd
then
  echo "This is my first command"
  echo "This is my second command"
  echo "I can even put in other commands besides echo:"
  ls -a /home/$testuser/.b*
fi

wsx@wsx-ubuntu:~/script_learn$ chmod u+x test3.sh
wsx@wsx-ubuntu:~/script_learn$ ./test3.sh
wsx:x:1000:1000:wsx,,,:/home/wsx:/bin/bash
This is my first command
This is my second command
I can even put in other commands besides echo:
/home/wsx/.bash_history  /home/wsx/.bashrc
/home/wsx/.bash_logout	 /home/wsx/.bashrc-anaconda3.bak

if command
then
  commands
else commands
fi

wsx@wsx-ubuntu:~/script_learn$ cat test5.sh
#!/bin/bash

# Testing nested ifs
#
testuser=NoSuchUser
#
if grep $testuser /etc/passwd
then
  echo "The user $testuser exits on this system."
else
  echo "The user $testuser does not exit on this system."
  if ls -d /home/$testuser/
  then
     echo "However, $testuser has a directory."
  fi
fi

wsx@wsx-ubuntu:~/script_learn$ chmod u+x test5.sh
wsx@wsx-ubuntu:~/script_learn$ ./test5.sh
The user NoSuchUser does not exit on this system.
ls: 无法访问'/home/NoSuchUser/': 没有那个文件或目录

if command1
then
truecommands
elif command2
then
truemore commands
fi

if [ condition ]
then commands
fi

wsx@wsx-ubuntu:~/script_learn$ cat test23.sh
#!/bin/bash
# using doble parenthesis
#
val1=10
#
if (( $val1 ** 2 > 90 ))
then
  (( val2 = $val1 ** 2 ))
  echo "The square of $val1 is $val2"
fi

wsx@wsx-ubuntu:~/script_learn$ chmod u+x test23.sh
wsx@wsx-ubuntu:~/script_learn$ ./test23.sh
The square of 10 is 100

wsx@wsx-ubuntu:~/script_learn$ cat test24.sh
#! /bin/bash
# using pattern matching
#
if [[ $USER == r* ]]
then
  echo "Hello $USER"
else
  echo "Sorry, I do not know you"
fi

wsx@wsx-ubuntu:~/script_learn$ chmod u+x test24.sh
wsx@wsx-ubuntu:~/script_learn$ ./test24.sh
Sorry, I do not know you

wsx@wsx-ubuntu:~/script_learn$ cat test25.sh
#!/bin/bash
# looking for a possible value
#
if [ $USER = "rich" ]
then
  echo "Welcome $USER"
  echo "Please enjoy you visit"
elif [ $USER = "barbara" ]
then
  echo "Welcome $USER"
  echo "Please enjoy you visit"
elif [ $USER = "testing" ]
then
  echo "Special testing account"
elif [ $USER = "jessica" ]
then
  echo "Do not forget to logout when you're done"

wsx@wsx-ubuntu:~/script_learn$ cat test26.sh
#!/bin/bash
# using the case command
#
case $USER in
rich | barbara)
  echo "Welcome, $USER"
  echo "Please enjoy your visits";;
testing)
  echo "Special testing account";;
jessica)
  echo "Do not forget to log off whe you're done";;
*)
  echo "Sorry, you are not allowed here";;
esac

wsx@wsx-ubuntu:~/script_learn$ chmod u+x test26.sh
wsx@wsx-ubuntu:~/script_learn$ ./test26.sh
Sorry, you are not allowed here

for var in list
do
truecommands
done

for var in list; do

wsx@wsx-ubuntu:~/script_learn$ cat test1
#!/bin/bash
# basic for command

for test in Alabama Alaska Arizona Arkansas California Colorado
do
    echo The next state is $test
done

wsx@wsx-ubuntu:~/script_learn$ ./test1
The next state is Alabama
The next state is Alaska
The next state is Arizona
The next state is Arkansas
The next state is California
The next state is Colorado

wsx@wsx-ubuntu:~/script_learn$ cat badtest1
#!/bin/bash
# another example of how not to use the for command

for test in I don't know if this'll work
do
    echo "word:$test"
done

wsx@wsx-ubuntu:~/script_learn$ ./badtest1
word:I
word:dont know if thisll
word:work

wsx@wsx-ubuntu:~/script_learn$ cat test2
#! /bin/bash
# another example of how not to use the for command

for test in I don\'t know if "this'll" work; do
echo  "word:$test"
done
wsx@wsx-ubuntu:~/script_learn$ ./test2
word:I
word:don't
word:know
word:if
word:this'll
word:work

wsx@wsx-ubuntu:~/script_learn$ cat test3
#!/bin/bash

# using a variable to hold the list
list="Alabama Alaska Arizona Arkansas Colorado"
list=$list" Connecticut" # 在尾部拼接文本

for state in $list; do
  echo "Have you ever visited $state?"
done

wsx@wsx-ubuntu:~/script_learn$ ./test3
Have you ever visited Alabama?
Have you ever visited Alaska?
Have you ever visited Arizona?
Have you ever visited Arkansas?
Have you ever visited Colorado?
Have you ever visited Connecticut?

wsx@wsx-ubuntu:~/script_learn$ cat test4
#!/bin/bash
# reading values from a file

file="states"

for state in $(cat $file)
do
    echo "Visit beautiful $state"
done

wsx@wsx-ubuntu:~/script_learn$ cat states
Alabama
Alaska
Arizona
Arkansas
Colorado
Connecticut
Delaware
Florida
Georgia
wsx@wsx-ubuntu:~/script_learn$ ./test4
Visit beautiful Alabama
Visit beautiful Alaska
Visit beautiful Arizona
Visit beautiful Arkansas
Visit beautiful Colorado
Visit beautiful Connecticut
Visit beautiful Delaware
Visit beautiful Florida
Visit beautiful Georgia

IFS=$'\n'

IFS.OLD=$IFS
IFS=$'\n'
<在代码中使用新的IFS值>
IFS=$IFS.OLD

IFS=:

IFS=$'\n':;"

wsx@wsx-ubuntu:~/script_learn$ cat test5
#!/bin/bash

# iterate through all the files in a directory

for file in /home/wsx/python_learn/*
do
  if [ -d "$file" ]
  then
    echo "$file is a directory"
  elif [ -f "$file" ]
  then
    echo "$file is a file"
  fi
done
wsx@wsx-ubuntu:~/script_learn$ ./test5
/home/wsx/python_learn/athletelist.py is a file
/home/wsx/python_learn/athletemodel.py is a file
/home/wsx/python_learn/ch2_data_input.py is a file
/home/wsx/python_learn/chapter5_first.py is a file
/home/wsx/python_learn/chapter6_first.py is a file
/home/wsx/python_learn/chapter6_second.py is a file
/home/wsx/python_learn/chapter6_third.py is a file
/home/wsx/python_learn/coinFlips.py is a file
/home/wsx/python_learn/Dive_into_python is a directory

for (( a = 1; a < 10; a++ ))

wsx@wsx-ubuntu:~/script_learn$ cat test6
#!/bin/bash

# testing the C-style for loop

for (( i=1; i <= 10; i++ ))
do
  echo "The next number is $i"
done

wsx@wsx-ubuntu:~/script_learn$ ./test6
The next number is 1
The next number is 2
The next number is 3
The next number is 4
The next number is 5
The next number is 6
The next number is 7
The next number is 8
The next number is 9
The next number is 10

while test command
do
  other commands
done

wangsx@SC-201708020022:~/tmp$ cat test
#/bin/bash
# while command test

var1=10
while [ $var1 -gt 0 ]
do
        echo $var1
        var1=$[ $var1 - 1 ]
done

wangsx@SC-201708020022:~/tmp$ ./test
10
9
8
7
6
5
4
3
2
1

wangsx@SC-201708020022:~/tmp$ cat test12
#!/bin/bash
# using the until command

var1=100

until [ $var1 -eq 0 ]
do
        echo $var1
        var1=$[ $var1 - 25 ]
done

wangsx@SC-201708020022:~/tmp$ ./test12
100
75
50
25

wangsx@SC-201708020022:~/tmp$ cat test14
#!/bin/bash
# nesting for loops

for (( a = 1; a <= 3; a++ ))
do
        echo "Starting loop $a:"
        for (( b = 1; b <= 3; b++ ))
        do
                echo "    Inside loop: $b"
        done
done

wangsx@SC-201708020022:~/tmp$ . test14
Starting loop 1:
    Inside loop: 1
    Inside loop: 2
    Inside loop: 3
Starting loop 2:
    Inside loop: 1
    Inside loop: 2
    Inside loop: 3
Starting loop 3:
    Inside loop: 1
    Inside loop: 2
    Inside loop: 3

wangsx@SC-201708020022:~/tmp$ cat test15
#!/bin/bash
# placing a for loop inside a while loop

var1=5

while [ $var1 -ge 0 ]
do
        echo "Outer loop: $var1"
        for (( var2 = 1; $var2 < 3; var2++))
        do
                var3=$[ $var1 * $var2 ]
                echo "  Inner loop: $var1 * $var2 = $var3"
        done
        var1=$[ $var1 - 1 ]
done

wangsx@SC-201708020022:~/tmp$ . test15
Outer loop: 5
  Inner loop: 5 * 1 = 5
  Inner loop: 5 * 2 = 10
Outer loop: 4
  Inner loop: 4 * 1 = 4
  Inner loop: 4 * 2 = 8
Outer loop: 3
  Inner loop: 3 * 1 = 3
  Inner loop: 3 * 2 = 6
Outer loop: 2
  Inner loop: 2 * 1 = 2
  Inner loop: 2 * 2 = 4
Outer loop: 1
  Inner loop: 1 * 1 = 1
  Inner loop: 1 * 2 = 2
Outer loop: 0
  Inner loop: 0 * 1 = 0
  Inner loop: 0 * 2 = 0

wangsx@SC-201708020022:~/tmp$ cat test16
#!/bin/bash
# using until and while loop

var1=3

until [ $var1 -eq 0 ]
do
        echo "Outer loop: $var1"
        var2=1
        while [ $var2 -lt 5 ]
        do
                var3=$(echo "scale=4; $var1 / $var2" | bc)
                echo "  Inner loop: $var1 / $var2 = $var3"
                var2=$[ $var2 + 1 ]
        done
        var1=$[ $var1 - 1 ]
done

wangsx@SC-201708020022:~/tmp$ . test16
Outer loop: 3
  Inner loop: 3 / 1 = 3.0000
  Inner loop: 3 / 2 = 1.5000
  Inner loop: 3 / 3 = 1.0000
  Inner loop: 3 / 4 = .7500
Outer loop: 2
  Inner loop: 2 / 1 = 2.0000
  Inner loop: 2 / 2 = 1.0000
  Inner loop: 2 / 3 = .6666
  Inner loop: 2 / 4 = .5000
Outer loop: 1
  Inner loop: 1 / 1 = 1.0000
  Inner loop: 1 / 2 = .5000
  Inner loop: 1 / 3 = .3333
  Inner loop: 1 / 4 = .2500

wangsx@SC-201708020022:~/tmp$ cat test
#!/bin/bash
for file in /home/*
do
        if [ -d "$file" ]
        then
                echo "$file is a directory"
        else
                echo "$file is a file"
        fi
done > output.txt
wangsx@SC-201708020022:~/tmp$ cat output.txt
/home/wangsx is a directory

wangsx@SC-201708020022:~$ cat test25
#!/bin/bash
# finding files in the PATH

IFS=:
for folder in $PATH
do
        echo "$folder:"
        for file in $folder/*
        do
                if [ -x $file ]
                then
                        echo "  $file"
                fi
        done
done

# 输出结果太多，我就不拷贝结果了

while IFS=',' read -r userid name

#!/bin/bash
# process new user accounts

input="users.csv"
while IFS=',', read -r userid name
do
trueecho "adding $userid"
trueuseradd -c "$name" -m $userid
done < "$input"

wsx@wsx-ubuntu:~$ date; who
2017年 07月 26日 星期三 09:53:43 CST
wsx      tty7         2017-07-26 09:48 (:0)

wsx@wsx-ubuntu:~/script_learn$ echo $PATH
/home/wsx/Anaconda/bin:/home/wsx/Anoconda/ENTER/bin:/usr/lib/jvm/default-java/bin:/home/wsx/bin:/home/wsx/Anaconda/bin:/usr/local/sbin:/usr/local/bin:/usr/sbin:/usr/bin:/sbin:/bin:/usr/games:/usr/local/games:/snap/bin

wsx@wsx-ubuntu:~/script_learn$ ./test1
bash: ./test1: 权限不够
wsx@wsx-ubuntu:~/script_learn$ ll test1 # 发现权限不够，查看文件的权限
-rw-rw-r-- 1 wsx wsx 73 7月  26 10:03 test1
wsx@wsx-ubuntu:~/script_learn$ chmod u+x test1 # 修改权限，添加可执行属性
wsx@wsx-ubuntu:~/script_learn$ ./test1 # 成功运行脚本
2017年 07月 26日 星期三 10:09:23 CST
wsx      tty7         2017-07-26 09:48 (:0)

wsx@wsx-ubuntu:~/script_learn$ echo This is a test
This is a test

wsx@wsx-ubuntu:~/script_learn$ echo "Let's see if this'll work"
Let's see if this'll work

#!/bin/bash
# This script displays the date and who's logged on
echo The time and date are:
date
echo "Let's see who's logged into the system"
who

wsx@wsx-ubuntu:~/script_learn$ ./test1
The time and date are:
2017年 07月 26日 星期三 10:17:59 CST
Let's see who's logged into the system
wsx      tty7         2017-07-26 09:48 (:0)

#!/bin/bash
# This script displays the date and who's logged on
echo -n "The time and date are: "
date
echo  "Let's see who's logged into the system: "
who

# 运行结果输出
wsx@wsx-ubuntu:~/script_learn$ ./test1
The time and date are: 2017年 07月 26日 星期三 10:24:04 CST
Let's see who's logged into the system:
wsx      tty7         2017-07-26 09:48 (:0)

wsx@wsx-ubuntu:~/script_learn$ cat test2
#! /bin/bash
# display user information from the system
echo "User info for userid: $USER"
echo UID: $UID
echo HOME: $HOME
wsx@wsx-ubuntu:~/script_learn$ chmod u+x test2
wsx@wsx-ubuntu:~/script_learn$ ./test2
User info for userid: wsx
UID: 1000
HOME: /home/wsx

wsx@wsx-ubuntu:~/script_learn$ cat test3
#!/bin/bash
# testing variables
days=10
guest="Katie"
echo "$guest checked in $days days ago"
days=5
guest="Jessica"
echo "$guest checked in $days days ago"
wsx@wsx-ubuntu:~/script_learn$ chmod u+x test3
wsx@wsx-ubuntu:~/script_learn$ ./test3
Katie checked in 10 days ago
Jessica checked in 5 days ago

wsx@wsx-ubuntu:~/script_learn$ cat test4
#!/bin/bash
# copy the /usr/bin directory listing to a log file
today=$(date +%y%m%d)
ls /usr/bin -al > log.$today

wsx@wsx-ubuntu:~/script_learn$ chmod u+x test4
wsx@wsx-ubuntu:~/script_learn$ ./test4

wsx@wsx-ubuntu:~/script_learn$ date > test6
wsx@wsx-ubuntu:~/script_learn$ ls -l test6
-rw-rw-r-- 1 wsx wsx 43 7月  26 16:42 test6
wsx@wsx-ubuntu:~/script_learn$ cat test6
2017年 07月 26日 星期三 16:42:34 CST

wsx@wsx-ubuntu:~/script_learn$ wc < test6
 1  6 43

wsx@wsx-ubuntu:~/script_learn$ wc << EOF
> test string1
> test string2
> test string3
> EOF
 3  6 39

wsx@wsx-ubuntu:~/script_learn$ cat test1
#!/bin/bash
# This script displays the date and who's logged on
echo -n "The time and date are: "
date
echo  "Let's see who's logged into the system: "
who
wsx@wsx-ubuntu:~/script_learn$ cat test1 | head -2 | sort
#!/bin/bash
# This script displays the date and who's logged on

wsx@wsx-ubuntu:~/script_learn$ exrpr 1 + 5
未找到 'exrpr' 命令，您要输入的是否是：
 命令 'expr' 来自于包 'coreutils' (main)
exrpr：未找到命令

wsx@wsx-ubuntu:~/script_learn$ var1=$[1+5]
wsx@wsx-ubuntu:~/script_learn$ echo $var1
6
wsx@wsx-ubuntu:~/script_learn$ var2=$[$var1+2]
wsx@wsx-ubuntu:~/script_learn$ echo $var2
8

wsx@wsx-ubuntu:~/script_learn$ bc
bc 1.06.95
Copyright 1991-1994, 1997, 1998, 2000, 2004, 2006 Free Software Foundation, Inc.
This is free software with ABSOLUTELY NO WARRANTY.
For details type `warranty'.
12 * 5.4
64.8
3.156 * (3 + 5)
25.248
quit

wsx@wsx-ubuntu:~/script_learn$ cat test9
#!/bin/bash
var1=$(echo "scale=4; 3.44/5" | bc)
echo The answer is $var1
wsx@wsx-ubuntu:~/script_learn$ chmod u+x test9
wsx@wsx-ubuntu:~/script_learn$ ./test9
The answer is .6880

wsx@wsx-ubuntu:~/script_learn$ cat test10
#!/bin/bash

var1=10.46
var2=43.67
var3=33.2
var4=71

var5=$(bc <<EOF
scale=4
a1 = ( $var1 * $var2)
b1 = ( $var3 * $var4)
a1 + b1
EOF
)

echo The final answer for this mess is $var5
wsx@wsx-ubuntu:~/script_learn$ chmod u+x test10
wsx@wsx-ubuntu:~/script_learn$ ./test10
The final answer for this mess is 2813.9882

wsx@wsx-ubuntu:~/script_learn$ date
2017年 07月 27日 星期四 10:44:18 CST
wsx@wsx-ubuntu:~/script_learn$ echo $?
0

wsx@wsx-ubuntu:~/script_learn$ asfg
未找到 'asfg' 命令，您要输入的是否是：
 命令 'asdfg' 来自于包 'aoeui' (universe)
asfg：未找到命令
wsx@wsx-ubuntu:~/script_learn$ echo $?
127

wsx@wsx-ubuntu:~/script_learn$ cat test13
#!/bin/bash
# testing the exit status
var1=10
var2=30
var3=$[$var1 + $var2]
echo The answer is $var3
exit 5

wsx@wsx-ubuntu:~/script_learn$ chmod u+x test13
wsx@wsx-ubuntu:~/script_learn$ ./test13
The answer is 40
wsx@wsx-ubuntu:~/script_learn$ echo $?
5