Unix overwrite file command

It gives an error because you can't have a file send its contents to itself, overwriting the data it is ending out. If you want to replace the original file, you pipe the data to a temporary file. When that operation is over, you then replace the original with the temporary file. If kernel designers allowd file descriptors to act as you are wanted to do with one operation, file systems would be corrupted extremely easily, files operations could be circular and grow without limits, etc.

There are complexities with file descriptor management and interprocess pipelining. Simple is good, robust and elegant. What you are hoping to do is better done in two shell operations, not one. Find all posts by Neo. Join Date: Oct Then it sounds like you are using csh or tcsh as your shell. In this case you have two options to force the overwriting of a file.

The first choice will affect all subsequent redirects in your current login. The second is one time only. You can also put "unset noclobber" into your. Command line overwrite. Hi all, as i have to deal every day with. Shell Programming and Scripting. Better to Delete or Overwrite. Here, we are copying contents of the bin directory to test directory. Alternatively, you can unalias the cp alias for the current session, then run your cp command in the non-interactive mode. TecMint is the fastest growing and most trusted community site for any kind of Linux Articles, Guides and Books on the web.

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Have a question or suggestion? Please leave a comment to start the discussion. Please keep in mind that all comments are moderated and your email address will NOT be published. Save my name, email, and website in this browser for the next time I comment. Notify me of followup comments via e-mail. Can overwritten files be recovered? Ask Question. Asked 7 years, 5 months ago. Active 2 months ago.

Viewed k times. Improve this question. Community Bot 1. Question Overflow Question Overflow 4, 18 18 gold badges 53 53 silver badges 79 79 bronze badges. You mean apart from your backups? All three examples you provided are implemented by deleting all the original file's data blocks and writing to newly-allocated blocks, and the procedure for recovering that data is the same as recovering a deleted file. An exception might be if the original files are exceedingly short shorter than 60 bytes on ext4 where the latter two examples likely make the previous data unrecoverable.

MarkPlotnick, according to Celada's comment, mv is different. Add a comment. Active Oldest Votes. The answer is "Probably yes, but it depends on the filesystem type, and timing. Improve this answer. Mark Plotnick Mark Plotnick Thank you for explaining the inner mechanics of the three different operations. This is really useful! If that doesn't get what you want, try again while subtracting 16 or 32, which will look at the areas that are and bytes less; files are often allocated in byte chunks.

If you're trying to recover a larger file, try larger counts to save time. That grep trick is amazing. You sir, are a savior. EerikSvenPuudist That can happen because grep tries to read the input line by line, and on disk partitions with random bytes, the lines can be very long.

A workaround is in the answer to this question. Show 13 more comments. Then search my-recovered-file for you string. AndyM AndyM 5 5 silver badges 12 12 bronze badges. I'm going to say no with a giant asterisk. Something that might be interesting to think about is fragmentation.

SailorCire SailorCire 2, 1 1 gold badge 14 14 silver badges 23 23 bronze badges. Your answer makes the assumption that a block-based non-copy-on-write filesystem such as ext4 or xfs is in use.

With copy on write filesystems such as zfs and btrfs you are in fact never "changing the block contents"; those filesystems always use brand new blocks to contain new data. Also, log-based filesystems like jffs2 also always write new data to new locations not "blocks", those filesystems are not block-based. That being said, this doesn't mean it's easy to find where the old data live and to do it before the space is recycled.

So your answer, which is no, is still correct — Celada. Celada Thanks! I found that very informative. I haven't had the time to look at how btrfs or zfs works, but I knew they exist. Stop or limit writes to your disk In this kind of situation is it best to limit any writes on the system at hand because you could really overwrite the data you want to keep. You can then just install 'testdisk' using something like example for debian : apt-get install testdisk Then launch "photorec" and let it restore files to a device partition different from the one that your data is located on.

I got 30 entries of diffent versions of the file, examining the bigger ones first. External service Depending on your expertise, there is also the option of subconstracting the job. Prepare To better cope with such a situation, prepare!