增加了cs246课堂笔记的补丁.

Also known as bash.

Command line shortcuts.

up/down arrows: review previous command
ctrl + a: move cursor to start of line
ctrl + e: move cursor to end of line
tab: try to complete the command or filename

Bash

man + theCommand 可以查看command说明.

uname用来check Unix version.

Input

## input和output使用>和<

cat < in.txt > out.txt

## 从in.txt用cat读取数据,输出到out.txt中

## 同时>>是append的意思

cat >> out

Every linux process has 3 streams, std in(standard input), std err(standard error), std out(standard output).

Why have a separate error stream

separate expected output from unexpected output(error)
stderr id NOT buffered

comd < in.txt > out.txt 2>err.log
comd > out.txt 2>&1

## 这里 2> 是std err 而&1 是std out,也就是coonect steam 2 to 1.
## 注意,这跟

comd 2>&1 > out.txt

## 不一样.

dev/null则是一个黑洞directory,可以用来skip output掉不需要的东西.

2>&1 redirect stderr to stdout.

Text editors

ed: edit text
vi: visual editing mode
vim: vi improved
emacs: editor macros
pico: pine composer
nano: 1000 times larger than pico

在学校里学的是vi,用vi写了很久的代码,从bash写到cpp.
结果被飞哥震惊:你怎么不用code editor.

谢谢教我.

cd

cd路径.

1	cd /User/document

cd后面斜杠是绝对路径.

cd ~

Back to home.

cd -

Last directory you were in.

Find

Grep

Search file content.

1	grep [-options] pattern filename

grep –E(egrep)

search for string or pattern based on extended regular expressions

grep –F(fgrep)

search for string data, ignoring the special meaning of any characters

Difference between egrep and grep:
The escape character rules are different.

Grep用于查询file里面是否有同样pattern的内容.
如果要查file类型,用string command.

Reading files

cat
more : can get paginated output
less : less replaced more, but less is more than more! (better memory use)

cat是学校里学过的,用来读取整个文件信息.
less更像是用来阅读的,可以选择部分文件,并上下移动.
用space or F key can read to the next page. B to the back page. H for help menu. Q for exit.

Overwriting

mv -f : force overwriting (default)
mv -n : no overwriting
mv -i : interactive overwriting, “ask me”
cp -R : recursive copy directories
cp -f : force overwriting (default if empty)
cp -n : no overwriting
cp -i : interactive overwriting, “ask me”

Symlink

一种快捷链接的意义.
可以把文件所在的directory存成一个快捷链接.

1	ln theDirectory linkName

要给directory instead of file 做symlink,有一点点不同.

1	ln -s theDirectory linkName

Kill a process

一般我会使用ctrl+c来终止一个程序,但这是属于还可以对着那个程序操作的情况.
由此run hexo,把窗口关掉了,就没法在对着那个在跑的hexo来终止它(找不到了嘛).

可以top(所有),ps(现在在run的)来check有什么process在running.
同时跑的程序也有PID,process ID.

ps –f full list of all your processes
jobs –l long list of background and stopped processes

知道PID后可以用kill command来终止程序.

1 2	kill PID kill -9 PID

有时用9有时不需要.

Header One	Header Two
kill pid	terminated and removed from memory
kill -9 pid	forcefully terminated
kill -19 pid	pauses, or stops a background process
kill -18 pid	restarts a stopped process into the background

ctrl + Z pauses, or stops, the foreground process.
nohup prevents a background process from aborting when you exit the shell.

1	nohup batchprog > bpresults 2> bperrors &

History

bash里可以查看history command.

history

同时也有command前的id.

1	!commandID

可以跑历史里的command.

还有种快捷跑history command的方法.

!cat

会跑出上一次使用cat的情况,比如cat sample.txt
也就是说忘记pass给cat的argument是什么也能再跑一次.

还有$会store上一次的argument.

1 2	nano sample.txt cat !$

第二行的cat可以默认成cat sample.txt

!3 : ref history cmmd #3
!-2 : ref cmmd which was two cmmd back
!cat : ref recent cmmd beginning with “cat”
!! : ref prev cmmd
!$ : ref prev cmmd arguments

sudo !!

Do the last command, but with sudo.

Unix file system

/bin : command/programs
/etc : configurations
/home : user home directories
/lib : system libraries
/tmp : temporary files
/usr : unix system resources
/var : variable system data files

Pipes

Connect the output(stdout) of one program to the input(stdin) of anothers.
(可以当作sql的nested querry来理解.)

prog1 | prog 2
## 等于

prog1 > temp 和 prog2 < temp

Example: Count the # of words in the first 20 lines of sample.txt.

1	head -20 sample.txt \| wc - w

Example: Suppose files words1.txt, words2.txt, etc. Contain words one per line. Print a dulicate free list if all words that occur in any of these files.

1	cat words*.txt \| sort \| uniq

Uniq remove the duplicate that adjcent to each other.

Use the output of a program as an argument to another program.

1	echo "Today is $(date) and I am $(whoami)"

Use $(command) to enable commands.

1	echo 'Today is $(date)'

This won’t work.
Single quote will suppress embedded commands.

这里更多syntax可以查看Cheatsheet中的Patterns.

Corn[https://en.wikipedia.org/wiki/Cron]

比较advance的 corn job command.
可以设定每天运行.

Script

Naming

255 char maximum
Use A-Z, a-z, 0-9, underscore, hyphen, period
Avoid \ / * & % ? | ^ ~ > < and other symbols
Case sensitive
Prefer underscores over spaces
Escape spaces with \
Use quotes around names with spaces

Coding

Shebang

如果要写shell script必须要加

1	#!/bin/bash

这一行叫做shebang line.
这一行必须是第一行顶头.#!叫做bang.
/bin/bash是the path to executable that will run your script.

Run

Assign execute permission, ensure stored in a directory within $PATH, and call it at command line:
```
 **listFiles**
```
Execute script in the current bash shell using the dot. Not recommended if script contains the exit command.
```
 **. listFiles**
```
Execute script in a bash sub-shell with bash command.
```
 **bash listFiles**
```

Debug

Add echo commands to display the variable value
Split code into chunks and test before moving on
Run script in trace mode:
1
bash -x listFiles

Variable

1 2	name=variable echo $name

Bash里的variable在命名时不可以有空格.
Name cannot start with a number
用variable的时候要加$ sign.

1
2
3

To pass an argument to the bash script, we use position parameters $1, $2, $3.

echo "Today is $1/$2/$3"

Header One	Header Two
$0	script name
$#	# of command line parameters
$*	all command line parameters
$@	all command line arguments
$?	exit status of the most recently executed command
$$	Process ID of the shell
$!	process ID of the most recently executed background command

Can also use read to read input.

#!/bin/bash

echo "Enter username : "
read nameVar
echo "Your username is $nameVar"

Bash里面还有array,牛逼.

#!/bin/bash
names[0]="Bob"
names[1]="Julie"
names[2]="Andrew"
names[3]="Alice"

1 2	#!/bin/bash names=("Bob" "Julie" "Andrew" "Alice")

We can access the entire array using *.

Arithmetic

We can use $((mathExpression)) or $[mathExpression].

echo $((4/2))
echo $[3+2*5]
result=$[3*5]
echo $result
num1=7
num2=2
num3=4
echo $[ ($num1-$num2) * $num3 ]

expr 4 + 7

Bash support integer arithmetic only, but we can use bc command for support of decimal places.

result1=$(echo "scale=3; 8/3" | bc)
echo $result1

result2=$(echo "scale=3; (8/3) ^ 3" | bc)
echo $result2

Function

#!/bin/bash
report(){
  if [ $1 -eq 31 ]; then
    echo "This month is the 31st."
  else
    echo "This month is the ${1}th"
  fi
}

function functionName(){
   code
}
# or
functionName(){
   code
}

Pass arguments.

#!/bin/bash
 
function displayUserDetails() {
  echo "Your name is $1 ."
  echo "You are $2 years old. "
}

displayUserDetails Alice 25
displayUserDetails Bob 32

Use echo to return a value from a function.

#!/bin/bash

function getName(){
   read -p "Enter your name : " name
   echo $name
}

echo "Your name is $(getName)"

By default function variables are global and available for use outside the function.
但是也可以单独define local的variable!

function cube() {
   x=$[ $1 * $1 * $1 ]
   local y=123
}
cube 3
echo "The cube of 3 is $x."
echo "The value of y is : $y."

The cube of 3 is 27.
The value of y is : .

Condition

if command
then
   code
fi

1
2
3

if command ; then
   code
fi

Both ok!

Else if statement.

if command1
then
   code
elif command2
then
   code
elif commandN
then
   code
else
   code
fi

Case statement.

case value in
   pattern1)
      code ;;
   pattern2)
      code ;;
   patternN)
      code ;;
   *)
      code ;;
esac

#!/bin/bash
cat<<eof
                ATM
        -------------------
        1. Deposit
        2. Withdraw
        -------------------
eof
read -p "Enter an option : " optVar

case $optVar in
   1) echo "Deposit option was selected." ;;
   2) echo "Withdraw option was selected." ;;
   *) echo "Invalid option." ;;
esac

1
2
3

if [ 5 –gt 3 ]
 then echo $?
fi

Spaces are required.

-e name File name exists.
-d name File name is a directory.
-f name File name is a regular file.
-h name File name is a symbolic link.
-r name File name exists and is readable.
-w name File name exists and is writeable.
-x name File name exists and is executable.
-s name File name exists and has nonzero size.

s1 = s2 String s1 equals string s2
s1 != s2 String s1 does not equal string s2
-z s1 String s1 has zero length
-n s1 String s1 has nonzero length

n1 –eq n2 Integer n1 and n2 are equal
n1 –ne n2 Integer n1 and n2 are not equal
n1 –lt n2 Integer n1 is less than n2
n1 –le n2 Integer n1 is less than or equal to n2
n1 –gt n2 Integer n1 is greater than n2
n1 –ge n2 Integer n1 is greater than or equal to n2

You can combine more than one expression by using conditional operators.

! t1 Negate operator. Negate the test

t1 II t2 OR operator. Either test t1 or test t2 are true
t1 –o t2 Shell syntax of OR

t1 && t2 AND operator. Both test t1 and test t2 are true
t1 –a t2 Shell syntax of AND

Loop

For loop.

for i in 1 2 3 4 5 6 7 8 9 10
do
	echo $i
done
# or
for ((i=1;i<=10;i++))
do
	echo $i
done
# or
for i in $*
do
	echo $i
done
# or
for file in $(ls)
do
	echo $file
done

While loop.

while [ condition ]
do
   command
done

while [ condition ] ; do
   command
done

Input redirection and a while loop can also be combined to read a file line by line.

#!/bin/bash
# script reads line by line the file that was passed
# as a command line argument

while read line
do
    echo $line
    sleep 0.5
done < $1

Until loop.

until [ condition ]
do
   command
done
# or
until [ condition ] ; do
   command
done

Exit

Parameters

详情可以看cheatsheet.

1 2	${1} 是这个script中第一个argument,以此类推 ${2} 是第二个. 也就是说如果被赋值, ${1} 是最先的收到值的.

定义variable的用法,
Rename all .cpp to .cc

举例:
mv Hello.cpp Hello.cc
(这里mv用来重命名)

filename=Hello.cpp
mv ${filename} ${filename%pp}c

%是drop的意思,在后面直接加上要加的内容“c”.

Condition

shell里的else if,注意,这里的空格相当重要.

if [ condition ]; then
 ...
elif [ condition ]; then
 ...
else
 ...
fi

fi是结束else if的意思.

Loop

1
2
3

while [ condition ]; do
 ...
done

CheatSheet

感谢cs246教授赞助的linux command summary.

Commands

Command	Meaning	Options
exit	log out
passwd	change your password
clear	clear screen
man command	show the manual page for command	man -k word show a list of man pages that mention word
history	show all previously-issued commands
!!	execute most recently-issued command
!c	execute most recently-issued command starting with c
whoami	display your login name
date	display current date and time
pwd	display current directory
ls	list contents of current directory	ls -a show all files, including hidden files
		ls -l show in long format
cp file1 file2	copy file1 to file2	cp -R dir1 dir2 recursively copy dir1 to dir2(including all the files in one dir)
mv file1 file2	move file1 to file2 (also use to rename)
rm file	remove file	can be used to recursively remove a directory, if -r option is used
touch file	update file’s last modified time to current time	can be used to create an empty file if file does not exist
cd dir	change directory to dir	cd - return to most recently visited directory
mkdir dir	create new directory dir in current directory	mkdir - p can specify more than one directory at once(including parent directory, like mkdir -p project1/project2)
rmdir dir	remove directory dir	only works if dir is empty; if not empty, use rm -r dir ; can specify more than directory at once
echo string	display string to screen
chmod perms file	set permissions on file to perms
chfn	change personal info (name, address, etc.) on Unix system
ps	display current processes	ps -a show all users’ processes
		ps -A show ALL processes (incl. system processes)
kill pid	kill process with number pid	kill -9 pid more forceful kill, for stubborn processes
who	show who is logged into this machine
finger username	show personal info for username
time command	show amount of time taken executing command
fg	bring background job to the foreground	useful if you accidentally ran vi or emacs with an &
find dir -name “pattern”	find all files whose names match pattern in dir and its subdirectories

Tools

Tool	Purpose	Options
cat f1 f2 …	display files f1, f2, … one after the other	cat -n f1 f2 … attaches line numbers
more file	cdisplay file one screen at a time
diff f1 f2	compare files f1 and f2 ; outputs instructions for converting f1 to f2	diff -w f1 f2 ignores whitespace
cmp f1 f2	compare files f1 and f2 ; outputs the first position where they differ
wc file	count the number of words, lines, and characters in file	wc -c file show just the number of characters
		wc -l file show just the number of lines
		wc -w file show just the number of words
egrep pat file	print all lines in file that contain pattern pat	egrep -n pat file print matching lines with line numbers
		egrep -v pat file print lines that do not match pat
head file	print first 10 lines of file	-num prints num lines (e.g. head -5 file)
tail file	like head, but prints last 10 lines of file
sort file	sorts the lines of file	sort -n file sorts strings of digits in numerical order
uniq file	removes consecutive duplicate lines from file	removes all duplicates if file is sorted

Programs

Program	Purpose	Options
vi file	invoke vi text editor on file
emacs file	invoke emacs text editor on file
pico file	invoke pico text editor on file
pine (or alpine)	read email
wget url	fetch file from the web at url
xpdf file	display pdf file
lpr file	print file to printer	lpr -Pljp 3016 file specifies the printers in MC3016
lpq	checks the print queue
lprm jobno	removes job jobno (must belong to you!) from print queue
ssh machine	make SSH connection to machine; opens a secure shell on remote machine; type exit to end SSH connection	ssh -Y (or -X) machine enable X forwarding (must have X server running on local machine)
scp mach1 :file1 mach2 :file2	securely copy file1 on mach1 to file2 on mach2	can omit mach1 if it is the local machine; similarly for mach2

Permissions

Permission can be changed with chmod.

How to read permission:

Symbol	Meaning
u	file’s owner
g	members of the file’s group, other than the owner
o	other users
a	all users (equivalent to ugo)
+	add permission bit
−	revoke permission bit
=	set permission bits exactly
r	read permission. for files—file’s contents can be read. for directories—directory’s contents can be listed
w	write permission. for files—file’s contents can be modified. for directories—files can be added/renamed/removed in the directory
x	execute permission. for files—file may be executed as a program or script. for directories—directory can be traversed (i.e. can cd into the directory)

chmod u+x dir3/filename
chmod o-r dir3
chmod ug+x,o-w file1
chmod a=rw file2

Octal	Text	Meaning
4	r	Read
2	w	Write
1	x	Execute
0		No permissions

1 2	chmod 751 dir3/filename chmod 750 dir3

Script Conditional Operators

Operator	Meaning
=	string equality
!=	string inequality
-eq	integer equality
-ne	integer inequality
-gt	integer greater than
-ge	integer greater than or equal to
-lt	integer less than
-le	integer less than or equal to
-a	and
-o	or
!	not
\ ( , \ )	parentheses for grouping
-d	file exists and is a directory
-e	file exists
-f	file exists and is a regular file
-r	file exists and is readable
-w	file exists and is writable
-x	file exists and is executable

Globbing Patterns(Wildcards)

Operator	Meaning
*	matches 0 or more characters
?	matches one character
[abxy]	matches exactly one of the characters in brackets
[!abxy]	matches any character except the ones in the brackets
[a-z]	matches any character in the given range
{pat1,pat2}	matches either pat1 or pat2 (technically not a glob; note no spaces)

Regular expression

Directories

Directory	Meaning
.	Current directory
..	Parent of current directory
~	Your home directory
/	Root directory
Starts with / or ~	Absolute path
Does not start with / or ~	Relative path

Variable

The exit command terminates the script and passes an exit status to the shell.
By convention, scripts should return 0 for success, and 1 or any non-zero value upon failure.
exit command with a non-zero exit status is useful for terminating a script when normal processing cannot continue.
If exit command is not used, the exit status of the script will be the exit status returned by the last command in the script

Underlake Reading Room

关于Unix的笔记

Bash

Input

Text editors

cd

Find

Grep

Reading files

Overwriting

Symlink

Kill a process

History

Unix file system

Pipes

Corn[https://en.wikipedia.org/wiki/Cron]

Script

Naming

Coding

Shebang

Run

Debug

Variable

Arithmetic

Function

Condition

Loop

Exit

Parameters

Condition

Loop

CheatSheet

Commands

Tools

Programs

Permissions

Script Conditional Operators

Globbing Patterns(Wildcards)

Directories

Variable