Writing code on a day when Mercury is retrograde is actually a shell combat task two weeks ago, but because I have been procrastinating and procrastinating, I did not finish it until this afternoon, thank me here group leader , his code is really weird (really unexpected)

First of all, the requirements of this actual combat are as follows:
1.The file names of this bunch of pictures are non-consecutive numbers
2.Change the filenames of this bunch of pictures to be consecutive
3.The original order of the pictures cannot be changed

E.g:

In order not to change the order of the pictures, save the sorted pictures to another folder

First edition:

#!/bin/bash
cd /home/computer/shell/practice/demo	

a=1
for file in $(ls)
do 
	name=${file%.*}
	NUM[a]=$name
	((a=a+1))
	echo "$name"
done


 
for (( i=1; i < a; i++));do
	ischanged=false
	for ((j=a-1; j> i; j--));do
		if [ ${NUM[j]} -lt ${NUM[j-1]} ];then
			temp=${NUM[j]}
			NUM[j]=${NUM[j-1]}
			NUM[j-1]=$temp
			ischanged=true
		fi
	done
	if [ ischanged = "false" ] ;then
	break;
	fi
done 

#for((i=1;i<a;i++));
#do
# 		echo "${NUM[$i]}"
 	
#done


for file in $(ls)
do
	mingzi=${file%.*}
	for((x=1;x<a;x++));
	do
		if [ $mingzi == ${NUM[$x]} ]
		then
		new=`printf "%05d\n" $x`		
		cp $file /home/computer/shell/practice/demo_new/$new.jpg
	
	fi
	done
done

It may be that I have learned a lot of C language. The first reaction is to write a sort, sort the collected file names and then output them, so I wrote a bubble sort. But the disadvantage is obvious. First of all, there is a lot of code, which is very annoying; and the sorting time is very long. If there are many pictures, it will be very slow. Then group leader Just say there is no need to sort (this is really impossible to think of)

second edition:

#!/bin/bash
cd /home/computer/shell/practice/demo	
a=1
for file in $(ls | sort -n)
do
	name=${file%.*}
	echo "$name"
	new=`printf "%05d\n" $a`		
	cp $file /home/computer/shell/practice/demo_new/$new.jpg
	((a=a+1))
done

The effect is as follows

After thinking about it for a long time, when I checked the data, I found that sort can be sorted, even numerically, so I had an idea. finished writing, group leader Said not bad, so the end of the flower.

Leader's code:

#!/bin/bash
cnt=0
for((i=0;i<20000;i++))
do
	if test -e JPEGImages/$i.jpg
	then 
		((cnt++))
		cp JPEGImages/$i.jpg jpeg_successed/$cnt.jpg
	else
		echo "file $i.jpg does not existed"
	fi
done

Because I'm really curious about what kind of situation can I not sort, so I'm coming group leader The code of the team leader is worthy of being the team leader. He wrote it in less than 13 lines, and even gave a hint to lose. But there is also a disadvantage. If there are only two pictures, one is called 1.jpg and the other is called 10000.jpg, it will take a long time.

Actual combat is used to learn knowledge, and this time is no exception

1. sort of shell

shell sort is an extension to insertion sort, but much faster than insertion sort.

Options	illustrate
-b	Ignore white space before each line
-d	Only consider spaces and alphabetic characters, numbers
-f	Ignore letter case
-m	Merge already sorted files without sorting
-n	Numeric comparison based on strings
-o	Write the sorted results to a file
-r	Sort in reverse order (the default sorting of sort is from top to bottom, from small to large, and the -n option can be used to flip the sorting)
-t	Specifies the separator character to use when sorting
-k	Specify the column (column, field) to be sorted
-u	ignore identical lines

This actual combat uses -n among them, for example:

Detailed explanation of sort command in shell

2. Get the file name and suffix of the shell

filename without directory

#Code:
file="thisfile.txt"
echo "filename: ${file%.*}"
echo "extension: ${file##*.}"
#output:
filename: thisfile
extension: txt 

filename with directory

var=/dir1/dir2/file.txt
echo ${var##*/}
file.txt
#extract suffix
echo ${var##*.}
txt
#Extract filename without suffix, in two steps
tmp=${var##*/}
echo $tmp
file.txt
echo ${tmp%.*}
file
#Extract directory
echo ${var%/*}
/dir1/dir2

3. test of shell

There is a test -e in the code of the group leader, but I have not learned this command, so I query.

Options	illustrate
-e	The [file name exists] (commonly used)
-f	Whether the [file name] exists and is a file (commonly used)
-d	Whether the [file name] exists and is a directory (commonly used)
-b	Whether the [file name] exists and is a block device
-c	Whether the [file name] exists and is a character device
-S	Whether the [file name] exists and is a Socket file
-p	Whether the [file name] exists and is a FIFO (pipe) file
-L	Whether the [file name] exists and is a linked file

test command (notes)

4. The ` symbol of shell

｀｀Inside is usually a shell command, before executing the script, this command will be executed first, which is equivalent to a function call

of shell syntax , ' ' , {},``, ,'',(),$(()) four grammatical meanings