What is the copy command in linux

The copy command under Linux is "cp". The cp command is mainly used to copy files and directories. The syntax "cp [option] source file target file" can copy one or more source files or directories to the specified file or directory; at the same time, with the help of certain options, copying can also be achieved. The entire directory, as well as functions such as comparing the old and new files and upgrading them.

#The operating environment of this tutorial: CentOS 6 system, Dell G3 computer.

The copy command under Linux is "cp".

The full English name of cp is "copy file", which means copying files in Chinese.

cp command is mainly used to copy files and directories. It can copy one or more source files or directories to the specified destination file or directory;

The basic format of the cp command is as follows:

cp [选项] 源文件 目标文件

Options:

• -a: Equivalent to the set of -d, -p, and -r options. We will introduce these options one by one;

• -d: If the source file is a soft link (invalid for hard links), the copied target file is also a soft link;

• -i: Ask, if the target file already exists, you will be asked whether to overwrite;

• -l: Create the target file as a hard link file of the source file, instead of copying the source file;

• -s: Create the target file as a soft link file of the source file instead of copying the source file;

• -p: The target file is retained after copying Source file attributes (including owner, group, permissions and time);

• -r: recursive copy, used to copy directories;

• -u: If the target file is different from the source file, use this option to update the target file. This option can be used to upgrade and backup the file.

It should be noted that there can be multiple source files, but in this case, the target file must be a directory.

Note: With certain options, the cp command can also copy the entire directory, compare the old and new files and upgrade them.

Example of using the cp command:

• [Example 1] Basic usage of the cp command

The cp command can copy both files and directories. Let’s first take a look at how to copy a file, for example:

[root@localhost ~]# touch cangls #建立源文件 [root@localhost ~]# cp cangls /tmp/ #把源文件不改名复制到 /tmp/ 目录下

If you need to rename the file, the command is as follows:

[root@localhost ~]# cp cangls /tmp/bols #改名复制

If a file with the same name already exists in the copy target location, you will be prompted whether to overwrite it. , because the cp command executes the alias of "cp -i" by default, for example:

[root@localhost ~]# cp cangls /tmp/ cp:是否覆盖"/tmp/cangls"?y #目标位置有同名文件，所以会提示是否覆盖

Next we look at how to copy a directory. In fact, you only need to use the "-r" option to copy a directory, for example:

[root@localhost ~]# mkdir movie #建立测试目录 [root@localhost ~]# cp -r /root/movie/ /tmp/ #目录原名复制

• [Example 2] Copy soft link file

If the source file is not an ordinary file, but a soft link file, then whether Can I copy the properties of a soft link? Let's try:

[root@localhost ~]# ln -s /root/cangls /tmp/cangls_slink #建立一个测试软链接文件/tmp/cangls_slink [root@localhost ~]# ll /tmp/cangls_slink lrwxrwxrwx 1 root root 12 6 月 14 05:53 /tmp/cangls_slink -> /root/cangls #源文件本身就是一个软链接文件 [root@localhost ~]# cp /tmp/cangls_slink /tmp/cangls_t1 #复制软链接文件，但是不加"-d"选项 [root@localhost ~]# cp -d /tmp/cangls_slink /tmp/cangls_t2 #复制软链接文件，加入"-d"选项 [root@localhost ~]# ll /tmp/cangls_t1 /tmp/cangls_t2 -rw-r--r-- 1 root root 0 6月 14 05:56 /tmp/cangls_t1 #会发现不加"-d"选项，实际复制的是软链接的源文件，而不是软链接文件 lrwxrwxrwx 1 root root 12 6 月 14 05:56/tmp/ cangls_t2-> /root/cangls #而如果加入了"-d"选项，则会复制软链接文件

This example shows that if the "-d" option is not used when copying a soft link file, the cp command copies the source file instead of the soft link file; only if "-" is added d" option, the soft link file will be copied. Please note that the "-d" option is invalid for hard links.

• [Example 3] Keep the source file attributes and copy

We found that after executing the copy command, the time of the target file will change to copy The execution time of the command, not the time of the source file. For example:

[root@localhost ~]# cp /var/lib/mlocate/mlocate.db /tmp/ [root@localhost ~]# ll /var/lib/mlocate/mlocate.db -rw-r-----1 root slocate2328027 6月 14 02:08/var/lib/mlocate/mlocate.db #注意源文件的时间和所属组 [root@localhost ~]#ll /tmp/mlocate.db -rw-r----- 1 root root2328027 6 月 14 06:05/tmp/mlocate.db #由于复制命令由root用户执行，所以目标文件的所属组为了root，而且时间也变成了复制命令的执行时间

When we perform backup and log backup, the time of these files may be an important parameter, so we need to execute the "-p" option. This option preserves the source file's attributes, including owner, group, and time. For example:

[root@localhost ~]# cp -p /var/lib/mlocate/mlocate.db /tmp/mlocate.db_2 #使用"-p"选项 [root@localhost ~]# ll /var/lib/mlocate/mlocate.db /tmp/mlocate.db_2 -rw-r----- root slocate 2328027 6月 14 02:08 /tmp/mlocate.db_2 -rw-r----- root slocate 2328027 6月 14 02:08 /var/lib/mlocate/mlocate.db #源文件和目标文件的所有属性都一致，包括时间

We have said before that the "-a" option is equivalent to the "-d, -p, -r" options. We have already talked about these options separately. So, when we use the "-a" option, all attributes of the target file and the source file are consistent, including the source file's owner, group, time and soft link. It is more convenient to use the "-a" option instead of the "-d, -p, -r" options.

• [Example 4] "-l" and "-s" options

If we use the "-l" option, the target file will be created as a hard link to the source file; if the "-s" option is used, the target file will be created as a soft link to the source file.

These two options are different from the "-d" option. The "d" option requires that the source file must be a soft link before the target file will be copied as a soft link; while "-l" and "-s" The source file of the " option only needs to be a normal file, and the target file can be directly copied as a hard link or soft link. For example:

[root@localhost ~]# touch bols #建立测试文件 [root@localhost ~]# ll -i bols 262154-rw-r--r-- 1 root root 0 6月 14 06:26 bols #源文件只是一个普通文件，而不是软链接文件 [root@localhost ~]# cp -l /root/bols /tmp/bols_h [root@localhost ~]# cp -s /root/bols /tmp/bols_s #使用"-l" 和"-s"选项复制 [root@localhost ~]# ll -i /tmp/bols_h /tmp/bols_s 262154-rw-r--r-- 2root root 0 6 月 14 06:26/tmp/bols_h #目标文件 /tmp/bols_h 为源文件的硬链接文件 932113 lrwxrwxrwx 1 root root 10 6 月 14 06:27/tmp/bols_s -> /root/bols #目标文件 /tmp/bols_s 为源文件的软链接文件

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