dd的作用是转换和拷贝文件,我们可以利用它来分割文件,相关的选项如下:
if=filename:输入的文件名
of=finename:输出的文件名
bs=bytes:一次读写的字节数,默认是512bytes
skip=blocks:拷贝前,跳过的输入文件的前blocks块,块的大小有bs决定
count=blocks:只拷贝输入文件的前blocks块
例如,现在有一个文件file,大小为116616字节:
- [root]# du -b file
- 116616 file
将其分割为两文件file1和file2,那我们就设置每块为1024字节,将file的前60块放入file1,余下的放入file2:
- [root]# dd if=file bs=1024 count=60 skip=0 of=file1
- [root]# dd if=file bs=1024 count=60 skip=60 of=file2
然后用cat将两个文件合并为file.bak,要注意文件的顺序:
- [root]# cat file1 file2 > file.bak
可以用md5sum验证一下file和file.bak:
- [root]# md5sum file
- 3ff53f7c30421ace632eefff36148a70 file
- [root]# md5sum file.bak
- 3ff53f7c30421ace632eefff36148a70 file.bak
可以证明两个文件时完全相同的。
为了方便分割、合并文件,我写了两个脚本:
ddf.sh:
- #ddf.sh:分割文件,分割后的文件以数字结尾,例如file分割为两个文件:file1和file2
- #!/bin/sh
- #使用脚本是第一参数是要分割的文件名
- Filename=$1
- Filesize=0
- Path=`pwd`
- #验证文件名是否正确,然后计算文件的大小
- if [ -z $Filename ];then
- echo “Error:The file name can not be empty”
- exit
- fi
- if [ -e $Filename ];then
- Filesize=`du -b $Filename | awk ‘{print $1}’`
- if [ $Filesize == 0 ];then
- echo “Error:The File size is zero!”
- exit
- fi
- echo “The file size is $Filesize Byte”
- echo “Plese enter the subfile size(KB):”
- else
- echo “Error:$Filename does not exist!”
- exit
- fi
- #输入分割后每个文件的大小,单位是KB
- read Subfilesize
- if [ -z $Subfilesize ];then
- echo “Error:Input can not be empty”
- exit
- fi
- echo $Subfilesize | grep ‘^[0-9]\+$’ >> /dev/null
- if [ $? -ne 0 ];then
- echo “Error:The Input is not a number!”
- exit
- elif [ $Subfilesize -eq 0 ];then
- echo “Error:The Subfile size is zero!”
- exit
- fi
- #计算需要分割为几个文件
- SubfileByte=`expr $Subfilesize \* 1024`
- Subfilenum=`expr $Filesize / $SubfileByte`
- if [ `expr $Filesize % $Subfilesize` -ne 0 ];then
- Subfilenum=`expr $Subfilenum + 1`
- fi
- #将文件分割
- echo “$Filename will be divided into $Subfilenum”
- i=1
- skipnum=0
- while [ $i -le $Subfilenum ]
- do
- echo “$Filename$i”
- dd if=$Filename of=“$Path/$Filename$i” bs=1024 count=$Subfilesize skip=$skipnum
- i=`expr $i + 1`
- skipnum=`expr $skipnum + $Subfilesize`
- done
- echo “$Filename has been divided into $Subfilenum”
- echo “Done !”
caf.sh:
- #caf.sh:合并文件,需要合并的文件要放在一个文件夹里
- # 文件名分为两个部分,第一部分都相同,第二部分必须是从1开始的连续数字,例如file1,file2,file3
- # 合并后的文件名为file.bak
- #!/bin/sh
- #输入文件名的第一部分
- echo “Please enter file name:”
- read Filename
- if [ -z $Filename ];then
- echo “Error:File name can not be empty”
- exit
- fi
- #输入待合并文件的个数
- echo “Please enter the number of subfiles:”
- read Subfilenum
- if [ -z $Subfilenum ];then
- echo “Error:The number of subfiles can not be empty”
- exit
- fi
- echo $Subfilenum | grep ‘^[0-9]\+$’ > /dev/null
- if [ $? -ne 0 ];then
- echo “Error:Input must be a number”
- exit
- fi
- if [ $Subfilenum -eq 0 ];then
- echo “Error:The number of subfiles can not be zero”
- exit
- fi
- #合并文件
- i=1
- Newfile=$Filename\.bak
- while [ $i -le $Subfilenum ]
- do
- Subfilename=$Filename$i
- if [ -e $Subfilename ];then
- echo “$Subfilename done!”
- cat $Subfilename >> $Newfile
- i=`expr $i + 1`
- else
- echo “Error:$Subfilename does not exist”
- rm -rf $Newfile
- exit
- fi
- done
- echo “Subfiles be merged into $Newfile”
- echo “Success!”
用这两个脚本完成对file的分割、合并:
- [root]# ./ddf.sh file
- The file size is 116616 Byte
- Plese enter the subfile size(KB):
- 60
- file will be divided into 2
- file1
- 记录了60+0 的读入
- 记录了60+0 的写出
- 61440字节(61 kB)已复制,0.0352612 秒,1.7 MB/秒
- file2
- 记录了53+1 的读入
- 记录了53+1 的写出
- 55176字节(55 kB)已复制,0.0316272 秒,1.7 MB/秒
- file has been divided into 2
- Done !
- [root]# ls
- caf.sh ddf.sh file file1 file2
- [root]# ./caf.sh
- Please enter file name:
- file
- Please enter the number of subfiles:
- 2
- file1 done!
- file2 done!
- Subfiles be merged into file.bak
- Success!
- [root]# ls
- caf.sh ddf.sh file file1 file2 file.bak