Shell programming enhancements

One shell

[3] shell Use of judgment in

（1） Judgment of numbers 
-eq  be equal to 
-ne  It's not equal to 
-gt  Greater than 
-ge  Greater than or equal to 
-lt  Less than 
-le  Less than or equal to 
（2） Logical operations 
&& ---> -a
|| ---> -o
! ---> !
（3） Judgment string 
-z  Determines if the string is empty 
-n  Judge whether the string is not empty 
= perhaps ==  Determines whether the strings are equal 
!=  Determines whether the strings are unequal 
\>  Judge whether it is greater than 
\<  Judge whether it is less than 
（4） Judgment of file type 
-e: Judge whether the file exists 
-s: Judge whether the file exists , And determine whether the file is empty 
-b: Judge whether the file exists , And determine whether the file is a block device file 
-c: Judge whether the file exists , And determine whether the file is a character device file 
-d: Judge whether the file exists , And determine whether the file is a directory 
-f: Judge whether the file exists , And determine whether the file is an ordinary file 
-L: Judge whether the file exists , And determine whether the file is a linked file 
-S: Judge whether the file exists , And determine whether the file is a socket file 
-p: Judge whether the file exists , And determine whether the file is a pipeline file 
（5） Judgment of file permissions 
-r: Judge whether it has readable permission 
-w: Determine whether you have writable permission 
-x: Judge whether it has executable permission 

#!/bin/bash
read -p "input filename> " file
if test -e "$file" -a -n "$file"
then
	if test -L $file
	then
		echo " This is the linked file "
	elif test -f $file
	then
		echo " This is an ordinary file "
	elif test -d $file
	then
		echo " This is a directory "
	elif test -c $file
	then
		echo " This is the character device file "
	elif test -s $file
	then
		echo " This is the socket file "
	elif test -p $file
	then
		echo " This is a g Pipeline files "
	fi
else
	echo "file not found ,please check input filename"
fi

practice `

Enter the name of a file into the script , Judge whether the input is not empty , If it's not empty , Judge whether it is a normal document If it's a regular document , Again
Judge whether the file has write permission. If the file does not have write permission, add write permission , Append... To the end of the file hello world this sentence .

#!/bin/bash
read -p "input filename >" file
if [ -n "$file" ]
then
	if [ -f "$file" ]
	then
		if [ ! -w "$file" ]
		then
			chmod u+w $file
		fi
		echo “hello world” >> $file
	else
		echo " The input is not an ordinary file "
		exit 1
	fi
else
	echo "input try again"
	exit 1
fi

[4] case in sentence

case  Variable  in
 Matching options 1)
 sentence 1;
 Matching options 2)
 sentence 2;
 Matching options n)
 sentence n;
 Format of matching options ：
*： Match any character 
[ character 1 character n]: matching [] Any character inside 
“y”|"yes" : If more than one can be used |
,|.|:|\"|?:  Note the user escape character 

#!/bin/bash
read -p "input number >" num
case $num in
	1)
		echo " Monday "
		;;
	2)
		echo " Tuesday "
		;;
	*)
		echo " Input error "
		;;
esac

#!/bin/bash
read -p "input char > " cc
case $cc in
	[0-9]|"10")
		echo " This is a number "	
		;;
	[a-zA-Z])
		echo " It's a letter "
		;;
	,|.|:|\"|?)
		echo " This is a punctuation mark "
		;;
	*)
		echo " Input error "
		;;
esac

[5] Loop statement

（1）while loop

while  The loop condition 
do
 The loop body 
done

#!/bin/bash
sum=0;
i=0;
while [ $i -le 100 ]
do
	((sum += i++))
done
echo $sum

practice 2

Create two directories under the user's home directory file-dir and dir-dir
If the directory already exists , There's no need to create , Ask the user if you need to empty the directory [Y/N] y n,yes no
Enter a path , Determine if this path exists , If there is , Copy the files in this directory to file-dir, Copy directory to
dir-dir Next
Count the number of copied files and directories , Print out the number of files and directories

#!/bin/bash
arr=("/home/jsetc/file-dir" "/home/jsetc/dir-dir")
i=0
while test $i -lt ${
    #arr[@]}
do
	if [ -d ${arr[$i]} ]
	then
		echo -n " Whether it is necessary to empty ${arr[$i]}  Catalog 【Y/N】}"
		read chose
		case $chose in
			"Y"|"y"|"yes"|"YES")
				echo " Emptying ${arr[$i]} in ..."
				rm -rf ${arr[$i]}/*
				echo "$arr[$i] It's been emptied ..."
				;;
			"N"|"n"|"no"|"NO")
				echo "${arr[$i]} The contents of the directory have not been emptied ..."
				;;
			*)
				echo " Input error "
				;;
		esac
	else
		mkdir ${arr[$i]}
		echo " New  ${arr[$i]} This directory "
	fi
	((i++))
done
while true
do
	file=0
	dir=0
	read -p " Enter the path to operate >" path
	if [ -d $path ]
	then
		arr1=(`ls $path`)
		j=0
		while test $j -lt ${
    #arr1[@]}
		do
			if [ -f $path/${arr1[$j]} ]
			then
				echo " Copying  ${arr1[$j]} file ..."
				cp $path/${arr1[$j]} ${arr[0]}
				((file++))
			elif [ -d $path/${arr1[$j]} ]
			then
				echo " Copying  ${arr1[$j]} Catalog ..."
				cp $path/${arr1[$j]} ${arr[1]} -r
				((dir++))
			fi
			((j++))
		done
	elif [ "$path" = "quit" ]
	then
		echo " Exit procedure ..."
		exit 1
	else
		echo " The path entered does not exist , Please try again ..."
		continue
	fi
	echo " Number of copied files :$file"
	echo " Number of copied directories :$dir"
done

（2）for loop

1. usage 1（c style ）

for((i = 0 ; i < 100;i++))
do
	 The loop body 
done

1. usage 2（shell Peculiar for loop ）

for  Variable  in  List of words 
do
	 The loop body 
done
 Be careful ： Format of word list 
 Format 1： Ubuntu windows ios redhat
 Format 2： `ls`
 Format 3：{start..end}
 Format 4： If in And the following word list is the default , At this time, the word list is the parameter of the command line 

#!/bin/bash
for var in ubuntu windows ios iphone
do
	echo $var
done

#!/bin/bash
for var in `ls`
do
	echo $var
done

#!/bin/bash
:<<EOF
sum=0
for var in {
    1..100}
do
	((sum += var))
done
echo $sum
EOF
for var in {
    A..Z}
do
	echo $var
done

1. select in Loop statements that enhance interaction

select  Variable  in  List of words 
do
	 The loop body 
done

#!/bin/bash
select var in windows ubuntu ios Android
do
	echo $var
done

#!/bin/bash
select var in windows ubuntu ios Android
do
	case $var in
		"windows")
			echo "welcome to windows"
			;;
		"ubuntu")
			echo "welcome to ubuntu"
			;;
		"ios")
			echo "welcome to ios"
			;;
		"Android")
			echo "welcome to Android"
			;;
		*)
			echo "error..."
			;;
	esac
done

[6] break and continue

 and c The rules of language grammar are the same , The syntax format is different 
break n  sign out n Layer cycle 
continue n  skip n Layer cycle , Execute next cycle 

[7] goto

 It is generally not recommended to use , Generally used for error handling