Split and merge files in Linux -- DD and cat

Dd is used to convert and copy objects. We can use it to split objects. The related options are as follows:

If = filename: Input File Name

Of = finename: output file name

BS = Bytes: the number of bytes read/write at a time. The default value is 512 bytes.

Skip = blocks: the blocks block before the input file is skipped. The size of the block is determined by BS.

Count = blocks: only copy the first blocks block of the input file.

 

For example, there is a file with a size of 116616 Bytes:

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1. [Root] # Du-B file
2. 116616 File

Split it into two files: file1 and file2. Set each file to 1024 bytes, put the first 60 parts of the file into file1, and the remaining parts to file2:

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1. [Root] # dd If = file BS = 1024 COUNT = 60 skip = 0 of = file1
2. [Root] # dd If = file BS = 1024 COUNT = 60 skip = 60 of = file2

Then use Cat to merge the two files into file. Bak. Pay attention to the order of the files:

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1. [Root] # Cat file1 file2> file. Bak

You can use md5sum to verify the file and file. Bak:

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1. [Root] # md5sum File
2. 3ff53f7c30421ace632eefff36148a70 File
3. [Root] # md5sum file. Bak
4. 3ff53f7c30421ace632eefff36148a70 file. Bak

It can be proved that the two files are identical.

 

To facilitate file splitting and merging, I wrote two scripts:

DDF. sh:

[Python]
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1. # DDF. sh: Split the file. The split file ends with a number. For example, the file is divided into two files: file1 and file2.
2. #! /Bin/sh
4. # Using the script is the first parameter: the file name to be split
5. Filename = $1
6. Filesize = 0
8. Path = 'pwd'
10. # Verify that the file name is correct and then calculate the file size
11. If [-Z $ filename]; then
12. Echo "error: the file name can not be empty"
13. Exit
14. Fi
15. If [-e $ filename]; then
16. Filesize = 'du-B $ filename | awk '{print $1 }''
17. If [$ filesize = 0]; then
18. Echo "error: the file size is zero! "
19. Exit
20. Fi
21. Echo "the file size is $ filesize Byte"
22. Echo "plese enter the subfile size (Kb ):"
23. Else
24. Echo "error: $ filename does not exist! "
25. Exit
26. Fi
28. # Input the size of each split file, in KB
29. Read subfilesize
30. If [-Z $ subfilesize]; then
31. Echo "error: input can not be empty"
32. Exit
33. Fi
35. Echo $ subfilesize | grep '^ [0-9] \ + $'>/dev/null
36. If [$? -Ne 0]; then
37. Echo "error: the input is not a number! "
38. Exit
39. Elif [$ subfilesize-EQ 0]; then
40. Echo "error: the subfile size is zero! "
41. Exit
42. Fi
44. # The calculation must be divided into several files.
45. Subfilebyte = 'expr $ subfilesize \ * 1024'
46. Subfilenum = 'expr $ filesize/$ subfilebyte'
47. If ['expr $ filesize % $ subfilesize '-Ne 0]; then
48. Subfilenum = 'expr $ subfilenum + 1'
49. Fi
51. # Splitting files
52. Echo "$ filename will be divided into $ subfilenum"
53. I = 1
54. Skipnum = 0
55. While [$ I-Le $ subfilenum]
56. Do
57. Echo "$ filename $ I"
58. Dd If = $ filename of = "$ path/$ filename $ I" BS = 1024 COUNT = $ subfilesize skip = $ skipnum
59. I = 'expr $ I + 1'
60. Skipnum = 'expr $ skipnum + $ subfilesize'
61. Done
62. Echo "$ filename has been divided into $ subfilenum"
63. Echo "done! "

 

CAF. sh:

[Python]
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1. # Caf. sh: Merge files. The files to be merged must be placed in a folder.
2. # The file name is divided into two parts, the first part is the same, the second part must be a continuous number starting from 1, such as file1, file2, file3
3. # The merged file name is file. Bak.
4. #! /Bin/sh
6. # Enter the first part of the file name
7. Echo "Please enter file name :"
8. Read filename
9. If [-Z $ filename]; then
10. Echo "error: file name can not be empty"
11. Exit
12. Fi
14. # Enter the number of files to be merged
15. Echo "Please enter the number of subfiles :"
16. Read subfilenum
17. If [-Z $ subfilenum]; then
18. Echo "error: the number of subfiles can not be empty"
19. Exit
20. Fi
21. Echo $ subfilenum | grep '^ [0-9] \ + $'>/dev/null
22. If [$? -Ne 0]; then
23. Echo "error: input must be a number"
24. Exit
25. Fi
26. If [$ subfilenum-EQ 0]; then
27. Echo "error: the number of subfiles can not be zero"
28. Exit
29. Fi
32. # Merge files
33. I = 1
34. Newfile = $ filename \. Bak
35. While [$ I-Le $ subfilenum]
36. Do
37. Subfilename = $ filename $ I
38. If [-e $ subfilename]; then
39. Echo "$ subfilename done! "
40. Cat $ subfilename> $ newfile
41. I = 'expr $ I + 1'
42. Else
43. Echo "error: $ subfilename does not exist"
44. Rm-RF $ newfile
45. Exit
46. Fi
47. Done
50. Echo "subfiles be merged into $ newfile"
51. Echo "success! "

 

Use these two scripts to split and merge files:

[Python]
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1. [Root] #./DDF. Sh File
2. The file size is 116616 byte
3. Plese enter the subfile size (Kb ):
4. 60
5. File will be divided into 2
6. File1
7. Read records of 60 + 0
8. Records 60 + 0 writes
9. 61440 bytes (61 KB) Copied, 0.0352612 seconds, 1.7 MB/second
10. File2
11. Records the reading of 53 + 1
12. Records write of 53 + 1
13. 55176 bytes (55 KB) Copied, 0.0316272 seconds, 1.7 MB/second
14. File has been divided into 2
15. Done!
16. [Root] # ls
17. CAF. Sh DDF. Sh file file1 file2
18. [Root] #./CAF. Sh
19. Please enter File Name:
20. File
21. Please enter the number of subfiles:
22. 2
23. File1 done!
24. File2 done!
25. Subfiles be merged into file. Bak
26. Success!
27. [Root] # ls
28. CAF. Sh DDF. Sh file file1 file2 file. Bak