Syntax structure for Bash shell scripts

Purpose: Self-collation, self-review, self-reflection!

Content: Dry Goods! Dry!! Dry!!!

Attach: The shortcomings of the hope that you correct, can give like me rookie a little inspiration is the best. Just the inspiration ...

Thank you: Thank the old boy (see your blog post and video, O (∩_∩) o haha ~), of course, there are online technology Daniel, reference book "UNIX Shell"

Bash Shell Scripting Structure

#/bin/sh	Shbang line, script interpreter. such as: #/bin/csh,#/bin/awk ... such as
#	Comments. such as: This doc is writed Chbo.
Shell metacharacters or wildcard characters	*, "," ",?, [],|,>,>>, etc. e.g. RM./*
Display output	echo "Hello,chbo."
Local variables	Var=value Var= ' value ' Var= "Value1 value2" Assign a value to a variable---the command result--- var= ' cmd ' var=$ (CMD)
Environment variables	---Temporary entry into force--- Export Var=value Var=value; export Var ---Permanent entry into force--- Write:/ROOT/.BASH_PROFILE/ROOT/.BASHRC Write normally:/etc/profile Script directory:/ETC/PROFILE.D
View variables	Echo $var _name Echo $PATH
Special variables	$ A: printing itself $n: ${10} $? : Echo $? Judging command Execution results $#: Number of parameters to be transmitted Such as: [email protected] 02]# cat 4.sh [$#-ne 2] && { echo "must" Exit 1 } echo haha
Pass the reference	---interactive--- [Email protected]]# read-t 5-p "pls input:" A Pls input:33 [Email protected]]# echo $a 33 ---non-interactive--- Var1=$1 Var2=$2
Arithmetic operations	1, ((n=1+2)) 2. n= ' expr 5 + 9 ' 3, let n=1+2 4, n= ' echo 3+3|BC ' 5, N=$[2+3]
	Way one: Test Mode two: [] Method Three: [[]] ---Numeric comparison-------------------------------- -eq-ge-gt-le-lt-ne such as: [$1-eq] ---string comparison------------------------------ = =! -N str1 Check if the length of the str1 is not 0 -Z str1 check str1 length is 0 Such as: ["$str 1" = "$str 2"] [-N "$str 1"]---> Check if a variable contains data Note: 1, plus " 2, = Both sides must have spaces /p> ---File comparison-------------------------------- -e -d-f -r -w -x (Excute)  -s (size -nt (new than)   -o Check that the file exists and belongs to the current user all -G checks whether a file exists with the same default group as the current user For example: [-S $file] Check if file exists not empty [$file 1-nt $file 2] Check file1 than file2 new
conditional statement	If [-f $file] Then  echo 0 Else  echo 1 Fi                 <===> [-F $file]&&echo 0| | Echo 1 ------------------------------------------- If [ ] Then  statements Elif Then  statements Elif Then  statements Else  statements If ------------------------------------------- Case Var_name in PATTERN1)  statements ;; Pattern2)  statements ;; Pattern3)  statements ;; *)  default value ;; Esac
Looping statements	For n in ' seq 10 ' Do Echo 10.0.0. $n Done --------------------------- While [] Do Commands Done ---------------------------- Until [] Do Commands Done
Function	Function name () { Instructions return n } Perform: Define the function before calling Calling functions, writing directly to the function name
Execution of the script	SH script_name chmod +x Path/script_name;path/script_name SOURCE Script_name or. Script_name (The current shell can invoke the contents of the script)

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Syntax structure for Bash shell scripts