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Thursday, February 13, 2014

Tutorial 3: Copy files, Hard Links and Soft Links

13. cp - cp command is used to copy the file from one location to another.

Eg. touch test1
cp test1 testdir/test2


The above set of commands will first create an empty file called test1. Then the file would be copied in another folder testdir and would be saved with name test2.











we can see the files below:
















The above screen print shows the touch command creating test1 file.

















The above screen shot shows the copy of test1 in testdir folder and named as test2.

Please note that cp command is different from mv. If you use mv instead of cp, a new file will not be created but rather the file would be moved from one location to another.

14. ln - ln command is used to create links to a file. Links can be of two types , soft link and hard link.
Lets create a hard link.

Eg.













In the above example we created an empty file called test1. Then we created a hard link to test1 as test2 using ln command. When we checked to contents of test1 and test2, both the files were empty. Then we added some text to test1 and verified it using cat command. Later we verified the contents of test2 using cat command. Note that the contents of test1 are also replicated in test2. Note that, test2 is not the actual file and hence will always have the size as 0 bytes as shown below.





















In order to create soft links, we can use ln command with -s.

Eg. ln -s test1 test1_soft

This will create a soft link named test1_soft for test1 file. It is shown below:


















Now, if the original file test1 is deleted, the contents of the hard link test2 will still remain but the soft link test1_soft will become unusable.








In above screenshot, test1 file is deleted however, a hard link test2 and soft link test1_soft are still present.
If you try to see the data in a hard link, it is still available.









However, when you try to see data in soft link, then  error appears.









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