Logical entities that contain data in a filesystem. Use this tag if your question: is about programs that create files (e.g. gzip, tar, zip); deals with characteristics of files (permissions, size, path/location); or is about management of files (renaming, listing, moving, removing). For operating ...

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83
votes
2answers
133k views

Empty the contents of a file

I am aware of three methods to delete all entries from a file. They are >filename touch filename filename < /dev/null Of these three I abuse >filename the most as that requires the ...
49
votes
4answers
34k views

Clone ownership and permissions from another file?

Is there a command or flag to clone the user/group ownership and permissions on a file from another file? To make the perms and ownership exactly "like" that of another file?
22
votes
8answers
42k views

Test if there are files matching a pattern in order to execute a script

I am trying to write an if statement to test whether there are any files matching a certain pattern. If there is a text file in a directory it should run a given script. My code currently: if [ -f /*...
35
votes
3answers
92k views

Sort based on the third column

I'm facing a huge 4-columns file. I'd like to display the sorted file in stdout based on its 3rd column: cat myFile | sort -u -k3 Is that enough to perform the trick?
23
votes
3answers
18k views

Determining if a file is a hard link or symbolic link?

I'm creating a shell script that would take a filename/path to a file and determine if the file is a symbolic link or a hard link. The only thing is, I don't know how to see if they are a hard link. ...
18
votes
3answers
5k views

I accidentally chmod -R +x on a directory. How do I restore the correct permissions?

Well, to be specific, it was chmod -R 755. Now every file is executable, which I don't want. I am thinking that I should look at the first two bytes of each file for the #!, but will this cover ...
14
votes
5answers
46k views

How do I append text to the beginning and end of multiple text files in Bash?

I have a directory full of text files. My goal is to append text to the beginning and end of all of them. The text that goes at the beginning and end is the same for each file. Based on code I got ...
18
votes
3answers
14k views

Can files be created with permissions set on the command line?

When creating directories, mkdir -m <mode> <dir> provides for creating one or more directories with the given mode/permissions set (atomically). Is there an equivalent for creating files, ...
9
votes
4answers
12k views

Renaming a bunch of files with date modified timestamp at the end of the filename?

So, say, I have a directory with a bunch of files like g.txt, where g.txt was last modified on, say, June 20, 2012. How would I batch-rename all of the files (like g.txt) with the last modified date ...
6
votes
1answer
247 views

Have a 'file' generate its content on demand? [duplicate]

Is there a way that I can have something which appears as a file, but when being read some code executes which fills the content of the file "on the fly"? Like FIFO/ named pipe, but without the need ...
5
votes
4answers
28k views

Linux file access monitoring

Is there any way in unix to find out who accessed certain file in last 1 week? It may be user or some script ftp it to some other place. Can I get a list of user name who accessed certain file? How ...
14
votes
3answers
3k views

How to copy a directory recursively using hardlinks for each file

I want to create a "copy" of a directory tree where each file is a hardlink to the original file Example: I have a directory structure: dirA/ dirA/file1 dirA/x/ dirA/x/file2 dirA/y/ dirA/y/file3 ...
9
votes
4answers
7k views

How are directories implemented in Unix filesystems?

My question is how directories are implemented? I can believe a data structure like a variable e.g. table, array or similar. Since UNIX is Open Source I can look in the source what the program does ...
8
votes
3answers
27k views

List of Recently Modified Files

How can I Get a list of all files modified , say 3 months ago. I checked this question but I was not able to apply it to my scenario. I am trying this now , it seems to be working , but I know there ...
7
votes
5answers
2k views

Delete all files in a directory whose name do not match a line in a file list

I have a directory with 1000+ files. In a text file, I have about 50 filenames, one per line. I'd like to delete all the files in the directory whose filenames don't correspond with an entry on the ...
7
votes
3answers
1k views

A virtual file containing the concatenation of other files

Is there a way of creating a filesystem object akin to this: mknod files p cat file1 file2 ... fileN > files but such that it can be seeked in, as if it were a regular file?
32
votes
7answers
3k views

Is it a UUOC (useless use of cat) to redirect one file to another?

If I want to make the contents of file2 match the contents of file1, I could obviously just run cp file1 file2. However, if I want to preserve everything about file2 except the contents—owner, ...
11
votes
6answers
21k views

How to remove blank lines from a file in shell?

I want to remove all empty lines from a file. Even if the line contains spaces or tabs it should also be removed.
8
votes
2answers
8k views

Group member cannot write even with write permission

The logged in user is a member of a group that has a write permission on a folder. But when this user is trying to write something, "permission is denied". The log below summarizes the question: ...
7
votes
4answers
13k views

Understanding of diff output

I have file1.txt this is the original text line2 line3 line4 happy hacking ! and file2.txt this is the original text line2 line4 happy hacking ! GNU is not UNIX if I do: ...
7
votes
3answers
535 views

How can I make a special file that executes code when read from [duplicate]

Most files on a Linux system are normal files, i.e. they are saved on disk and reading from them just reads from a specified chunk of memory on the disk. How can I make something that behaves like a ...
6
votes
2answers
6k views

“no such file or directory” message when deleting a file that exists on NTFS

I have a directory with images. Suddenly I found out that there's a new image with a new name. The image content is similar to another image in another directory but with a different name. I didn't ...
5
votes
2answers
2k views

Back up and restore file permissions

Is there a way to back up and restore file ownership and permissions (the things that can be changed with chown and chmod)? You can do this in Windows using icacls. What about access control lists?
10
votes
8answers
942 views

sed in-place line deletion on full filesystem?

Due to an application bug as yet undiagnosed, I have several hundred servers with a full disk. There is one file that has been filled up with duplicate lines—not a log file, but a user environment ...
8
votes
2answers
790 views

Cleaner way to delete files on Linux which include a datestamp as part of file name

I have a new requirement to purge MySQL dump files that are older than 30 days. The files use a naming convention of "all-mysql-YYYYMMDD-HHMM.dump". The files are located on SAN mounted file system, ...
7
votes
2answers
13k views

What is nobody user and group?

On my server (Synology DS212) some files and folders have nobody nobody users and groups. What are the characteristics of this user and group? Who can write of read this file? How can I change it ? ...
6
votes
3answers
8k views

Write access without read access

Is it possible for a user to have a write access to a file and not be able to read it? How is it possible? I tried the following commands: debianbox@debian:~/posix/io$ touch filetest debianbox@...
5
votes
5answers
528 views

Rename files based on their parent directory using find/xargs command?

I have a directory structure like this: Project/ | +--Part1/ | | | +--audio.mp3 | +--Part2/ | | | +--audio.mp3 | +--Part3/ | | | +--audio.mp3 ... I want to ...
4
votes
4answers
12k views

get age of given file

How can I get the age of a given file in, at least, days? I'm well aware of ls -lh and similar commands. I want something that will work sort of like this: getfage <FILE> # prints out '12d' (...
1
vote
5answers
225 views

List (or move) only files with a certain number of lines?

Dealing with a whole bunch of two-line config files, I'd like a way to exclude any files that have a different number of lines. So, something like: mv * destdir only if file contains exactly two ...
4
votes
4answers
375 views

Remove a directory from inside using the command line interface [duplicate]

Imaging the next simple file structure within the /home/user/ directory: /home/user |--dir0 |--dir1 |--file1 My current directory is 'dir1' and I remove the ...
4
votes
2answers
2k views

Access history of a file [duplicate]

I was wondering if there are any tools to keep track of the access history of a file. I know of stat, but as far as I understand, it only returns information about the last time the file was accessed.
3
votes
1answer
196 views

How to limit speed of file copy?

I am copying huge file from NFS mount using dd: dd if=/mnt/nfs/image.img of=/dev/sda I need to limit the speed of reading from NFS. How can I achieve it? The only precondition is to use some easy ...
3
votes
4answers
500 views

Determining the number of files and subdirectories in Linux

When displaying directories in linux using ls -ld, I get something like this: user@shell:~/somedirectory$ ls -ld drwxr-xr-x 2014 K-rock users 65536 20011-11-05 11:34 user@shell:~/somedirectory$ ...
3
votes
2answers
442 views

Outputting common lines from 2 files and uncommon lines from both the files in one output file

I have 2 text files. Lets name them file1.txt and file2.txt file1.txt is as follows chr10 181144 225933 chr10 181243 225933 chr10 181500 225933 chr10 226069 255828 chr10 255989 267134 ...
1
vote
1answer
118 views

Saving process output to a file in systemd unit file

I created a systemd file unit (Centos 7) and I wanted to save the Python output to a file but the service won't start with the below code. [root@static ~]# cat /etc/systemd/system/pykms.service [Unit]...
64
votes
4answers
21k views

locate vs find: usage, pros and cons of each other

In Linux and Unix systems there are two common search commands: locate and find. What are the pros and cons of each? When one have benefits over the other?
21
votes
5answers
249k views

How to create a simple .txt (text) file using terminal? [closed]

I'm just trying to review basic terminal commands. Having said that, how do I create a text file using the terminal only?
78
votes
9answers
129k views

How can I get the size of a file in a bash script?

How can I get the size of a file in a bash script? How do I assign this to a bash variable so I can use it later?
49
votes
7answers
4k views

How are file types known if not from file suffix?

I would like to know how file types are known if filenames don't have suffixes. For example, a file named myfile could be binary or text to start with, how does the system know if the file is binary ...
31
votes
4answers
24k views

Reading lines from a file with bash: for vs. while

I'm trying to read a text file and do something with each line, using a bash script. So, I have a list that looks like this: server1 server2 server3 server4 I thought I could loop over this using ...
28
votes
4answers
18k views

How to properly and easy configure `xdg-open` without any enviroment?

I'm using OpenBox window manager without any desktop enviroment. xdg-open behaves strangely. It opens everything with firefox. $ xdg-settings --list Known properties: default-web-browser ...
20
votes
5answers
20k views

How to copy directories with preserving hardlinks?

How to move directories that have files in common from one to another partition ? Let's assume we have partition mounted on /mnt/X with directories sharing files with hardlinks. How to move such ...
34
votes
6answers
7k views

How does Linux choose which application to open a file?

If a file tells the OS its file format, how does the OS choose which application to open it by default? In Windows, is the association stored in the registry table? How does Linux choose which ...
22
votes
3answers
93k views

undelete a just deleted file on ext4 with extundelete

Is there a simple option on extundelete how I can try to undelete a file called /var/tmp/test.iso that I just deleded? (it is not so important that I would start to remount the drive read-only or ...
21
votes
2answers
24k views

What does the 'd' mean in ls -al results and what is that slot called? [duplicate]

In Linux, what does the d mean in the first position of drwxr-xr-x? And what are all of the possible letters that could be there, and what do they mean? I'm trying to learn more about the Linux file ...
18
votes
2answers
25k views

Fastest way to concatenate files

I've got 10k+ files totaling over 20GB that I need to concatenate into one file. Is there a faster way than cat input_file* >> out ? The preferred way would be a bash command, Python is ...
17
votes
3answers
21k views

Quickly find which file(s) belongs to a specific inode number

I know of this command: find /path/to/mountpoint -inum <inode number> but it is a very slow search, I feel like there has to be a faster way to do this. Does anybody know a faster method?
46
votes
2answers
4k views

Why is rm allowed to delete a file under ownership of a different user?

From the post Why can rm remove read-only files? I understand that rm just needs write permission on directory to remove the file. But I find it hard to digest the behaviour where we can easily delete ...
14
votes
3answers
58k views

granting write permissions to a group to a folder

How can I grant write permission to 1 group ? I have 2 users (alex and ben). alex is member of group alex and of group consult. ben is member of group ben and of group consult. I want to grant read ...