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103.3. Perform basic file management

103.3 Perform basic file management

Weight: 4
Description: Candidates should be able to use the basic Linux commands to manage files and directories.
Key Knowledge Areas:
  • Copy, move and remove files and directories individually
  • Copy multiple files and directories recursively
  • Remove files and directories recursively
  • Use simple and advanced wildcard specifications in commands
  • Using find to locate and act on files based on type, size, or time
  • Usage of tar, cpio and dd
Terms and Utilities:
  • cp
  • find
  • mkdir
  • mv
  • ls
  • rm
  • rmdir
  • touch
  • tar
  • cpio
  • dd
  • file
  • gzip
  • gunzip
  • bzip2
  • xz
  • file globbing
As we said Linux is the world of processes and files, in this section we start talking about file management in linux and we will talk about both files and directories (folders). Tools are pretty basic and their names are abstraction of what they really do.

ls

ls lists files and directories, and their associated metadata, such as file size, ownership, and modification time.
ls [options] [file|dir]
We can use absolute paths (ex:user1@ubuntu16-1:~$ ls /home/user1/Music) or relative paths (ex: user1@ubuntu16-1:~$ ls Music/) with ls.
With no options, ls lists the files contained in the current directory, sorting them alphabetically.
user1@ubuntu16-1:~$ ls
Desktop Downloads Music Public Videos
Documents examples.desktop Pictures Templates
-1 prints outs each result in 1 line:
user1@ubuntu16-1:~$ ls -1
Desktop
Documents
Downloads
examples.desktop
Music
Pictures
Public
Templates
Videos
The default output of the ls command shows only the names of the files, which is not very informative. So lets use ls with -l for long listing format :
user1@ubuntu16-1:~$ ls -l
total 44
drwxr-xr-x 2 user1 user1 4096 Nov 4 2018 Desktop
drwxr-xr-x 2 user1 user1 4096 Nov 4 2018 Documents
drwxr-xr-x 2 user1 user1 4096 Nov 4 2018 Downloads
-rw-r--r-- 1 user1 user1 8980 Apr 20 2016 examples.desktop
drwxr-xr-x 2 user1 user1 4096 Nov 4 2018 Music
drwxr-xr-x 2 user1 user1 4096 Nov 4 2018 Pictures
drwxr-xr-x 2 user1 user1 4096 Nov 4 2018 Public
drwxr-xr-x 2 user1 user1 4096 Nov 4 2018 Templates
drwxr-xr-x 2 user1 user1 4096 Nov 4 2018 Videos
The first character represents the file type: "-" for a regular file, "d" for a directory, "l" for a symbolic link(we will see them).
When the long listing format is used the ls command will display the following file information:
  1. 1.
    The file type
  2. 2.
    The file permissions
  3. 3.
    Number of hard links to the file
  4. 4.
    File owner
  5. 5.
    File group
  6. 6.
    File size
  7. 7.
    Date and Time
  8. 8.
    File name
Show Hidden Files
By default, the ls command will not show hidden files. In Linux, a hidden file is any file that begins with a dot (.).To display all files including the hidden files use the -a option:
user1@ubuntu16-1:~$ ls -a
. .config .gconf Pictures .Xauthority
.. Desktop .gnupg .profile .xsession-errors
.bash_history .dmrc .ICEauthority Public .xsession-errors.old
.bash_logout Documents .local .ssh
.bashrc Downloads .mozilla Templates
.cache examples.desktop Music Videos
Some other usefull options:
ls command options
description
-l
list with long format - show permissions
-r
list in reverse order
-t
sort by time & date
-lh
List Files with Human Readable Format
-F
List Files and Directories with ‘/’ Character at the end
-R
Recursively list Sub-Directories
-a
list all files including hidden file starting with '.'

Copying, Moving & Deleting

To make it easier lets classfied them in some groups:
Before going into how to use the touch command, let’s start by reviewing the file timestamps in Linux.

Linux Files Timestamps

In Linux every single file is associated with timestamps, and every file stores the information of last access time, last modification time and last change time. So, whenever we create new file, access or modify an existing file, the timestamps of that file automatically updated.
A file in Linux has three timestamps:
  • atime (access time) - The last time the file was accessed/opened by some command or application such as cat, vim or grep.
  • mtime (modify time) - The last time the file’s content was modified.
  • ctime (change time) - The last time the file’s attribute or content was changed. The attribute includes file permissions, file ownership or file location.
To display the file status including the timestamps you can use the stat command.(we use ubuntu 16.04 here)
root@ubuntu16-1:~# stat /etc/hosts
File: '/etc/hosts'
Size: 247 Blocks: 8 IO Block: 4096 regular file
Device: 801h/2049d Inode: 1200795 Links: 1
Access: (0644/-rw-r--r--) Uid: ( 0/ root) Gid: ( 0/ root)
Access: 2019-09-08 02:34:44.962514623 -0700
Modify: 2018-07-01 23:15:30.140815060 -0700
Change: 2018-07-01 23:15:30.144817112 -0700
Birth: -

touch

The touch command is a standard command used in UNIX/Linux operating system which is used to create, change and modify timestamps of a file.
  • touch command (with no option) create an empty file if file does not exist.
  • if file exists touch command would change its time stamps .
creating an empty file:
touch command is used to create a file without any content. The file created using touch command is empty. This command can be used when the user doesn’t have data to store at the time of file creation.
touch file_name
example:
root@ubuntu16-1:~/test-space# touch file1
root@ubuntu16-1:~/test-space# ls -l
total 0
-rw-r--r-- 1 root root 0 Sep 8 02:37 file1
creating multiple empty files:
touch File1_name File2_name File3_name
for example:
root@ubuntu16-1:~/test-space# ls -l
total 0
-rw-r--r-- 1 root root 0 Sep 8 02:37 file1
root@ubuntu16-1:~/test-space# touch file1 file2 file3
root@ubuntu16-1:~/test-space# ls -l
total 0
-rw-r--r-- 1 root root 0 Sep 8 02:44 file1
-rw-r--r-- 1 root root 0 Sep 8 02:44 file2
-rw-r--r-- 1 root root 0 Sep 8 02:44 file3
avoids creating new files:
root@ubuntu16-1:~/test-space# touch -c file4
root@ubuntu16-1:~/test-space# ls -l
total 0
-rw-r--r-- 1 root root 0 Sep 8 02:44 file1
-rw-r--r-- 1 root root 0 Sep 8 02:44 file2
-rw-r--r-- 1 root root 0 Sep 8 02:44 file3
-coption tells that if the file does not exist, do not create it:

touch command timestamp options:

  • -a: change the access time only
  • -d: update the access and modification times
  • -m: change the modification time only
  • -r: use the access and modification times of other file as reference.
  • -t: creates a file using a specified time
Lets do some timestamp modifications.
Create a file using a specified time:touch -t YYMMDDHHMM fileName
root@ubuntu16-1:~/test-space# touch -t 9812010510 myfile
root@ubuntu16-1:~/test-space# ls -l | grep myfile
-rw-r--r-- 1 root root 0 Dec 1 1998 myfile
root@ubuntu16-1:~/test-space# stat myfile
File: 'myfile'
Size: 0 Blocks: 0 IO Block: 4096 regular empty file
Device: 801h/2049d Inode: 2228284 Links: 1
Access: (0644/-rw-r--r--) Uid: ( 0/ root) Gid: ( 0/ root)
Access: 1998-12-01 05:10:00.000000000 -0800
Modify: 1998-12-01 05:10:00.000000000 -0800
Change: 2019-09-08 03:19:28.410459835 -0700
Birth: -
Change the access time:touch -a fileName
root@ubuntu16-1:~/test-space# touch -a myfile
It only updates last access time.
root@ubuntu16-1:~/test-space# stat myfile
File: 'myfile'
Size: 0 Blocks: 0 IO Block: 4096 regular empty file
Device: 801h/2049d Inode: 2228284 Links: 1
Access: (0644/-rw-r--r--) Uid: ( 0/ root) Gid: ( 0/ root)
Access: 2019-09-08 03:26:42.378185145 -0700
Modify: 1998-12-01 05:10:00.000000000 -0800
Change: 2019-09-08 03:26:42.378185145 -0700
Change the modification time:touch -m fileName
root@ubuntu16-1:~/test-space# touch -m myfile
It only updates last modification time.
root@ubuntu16-1:~/test-space# stat myfile
File: 'myfile'
Size: 0 Blocks: 0 IO Block: 4096 regular empty file
Device: 801h/2049d Inode: 2228284 Links: 1
Access: (0644/-rw-r--r--) Uid: ( 0/ root) Gid: ( 0/ root)
Access: 2019-09-08 03:26:42.378185145 -0700
Modify: 2019-09-08 03:28:06.314537292 -0700
Change: 2019-09-08 03:28:06.314537292 -0700
Birth: -
Explicitly Set the Access and Modification times: touch -c -t YYDDHHMM filename
Update access and modification time:touch -c -d fileName
We use the timestamp of another file with -r option: touch -r refrence_file_name file_name
root@ubuntu16-1:~/test-space# stat file1
File: 'file1'
Size: 0 Blocks: 0 IO Block: 4096 regular empty file
Device: 801h/2049d Inode: 2228281 Links: 1
Access: (0644/-rw-r--r--) Uid: ( 0/ root) Gid: ( 0/ root)
Access: 2019-09-08 02:44:27.744736670 -0700
Modify: 2019-09-08 02:44:27.744736670 -0700
Change: 2019-09-08 02:44:27.744736670 -0700
Birth: -
root@ubuntu16-1:~/test-space# touch -r file1 myfile
root@ubuntu16-1:~/test-space# stat myfile
File: 'myfile'
Size: 0 Blocks: 0 IO Block: 4096 regular empty file
Device: 801h/2049d Inode: 2228284 Links: 1
Access: (0644/-rw-r--r--) Uid: ( 0/ root) Gid: ( 0/ root)
Access: 2019-09-08 02:44:27.744736670 -0700
Modify: 2019-09-08 02:44:27.744736670 -0700
Change: 2019-09-08 03:34:14.724762374 -0700
Birth: -
and many more examples.

mkdir

mkdir command in Linux allows the user to create directories (also referred to as folders in some operating systems )
mkdir [options...] [directories ...]
root@ubuntu16-1:~/test-space# mkdir dir1
root@ubuntu16-1:~/test-space# ls -l
total 4
drwxr-xr-x 2 root root 4096 Sep 8 03:44 dir1
This command can create multiple directories at once as well as set the permissions for the directories. It is important to note that the user executing this command must have enough permissions to create a directory in the parent directory, or he/she may recieve a ‘permission denied’ error.
root@ubuntu16-1:~/test-space# mkdir --help
Usage: mkdir [OPTION]... DIRECTORY...
Create the DIRECTORY(ies), if they do not already exist.
​
Mandatory arguments to long options are mandatory for short options too.
-m, --mode=MODE set file mode (as in chmod), not a=rwx - umask
-p, --parents no error if existing, make parent directories as needed
-v, --verbose print a message for each created directory
-Z set SELinux security context of each created directory
to the default type
--context[=CTX] like -Z, or if CTX is specified then set the SELinux
or SMACK security context to CTX
--help display this help and exit
--version output version information and exit
​
GNU coreutils online help: <http://www.gnu.org/software/coreutils/>
Full documentation at: <http://www.gnu.org/software/coreutils/mkdir>
or available locally via: info '(coreutils) mkdir invocation'
Lets try some of the most useful switches, -penables the command to create parent directories as necessary. If the directories exist, no error is specified:
root@ubuntu16-1:~/test-space# mkdir -p dir1/floor1/floor2
root@ubuntu16-1:~/test-space# tree
.
└── dir1
└── floor1
└── floor2
​
3 directories, 0 files
We can create a directory and set the permissions(will be discussed later) for that directory at the same time using -m option:
root@ubuntu16-1:~/test-space# mkdir -m777 dir2
root@ubuntu16-1:~/test-space# ls -l
total 8
drwxr-xr-x 3 root root 4096 Sep 8 03:57 dir1
drwxrwxrwx 2 root root 4096 Sep 8 04:09 dir2
The syntax of the mode is the same as the chmod command (will be discussed later).
root@ubuntu16-1:~/test-space# mkdir -v -m o=--- dir3
mkdir: created directory 'dir3'
root@ubuntu16-1:~/test-space# ls -l
total 12
drwxr-xr-x 3 root root 4096 Sep 8 03:57 dir1
drwxrwxrwx 2 root root 4096 Sep 8 04:09 dir2
drwxr-x--- 2 root root 4096 Sep 8 04:14 dir3
with -voption, it prints a message for each created directory.

cp

The cp command is a command-line utility for copying files and directories. [Copies of files are independent of the original file( unlike the mv command) ].The basic syntax of the cp command is:
cp [options….] source(s) destination
cp can take 1 or more sources(s) but just one destination.
It supports copying one or more files or directories with options for taking backups and preserving attributes.
Do not forget to consider source and destination types (files or directory) when using cp command.
  • If the target is an existing directory, then all sources are copied into the target.
  • If the target is a directory that does not exist, then the (single) source must also be a directory and a copy of the source directory and its contents is made with the target name as the new name.
  • If the target is a file, then the (single) source must also be a file and a copy of the source file is made with the target name as the new name, replacing any existing file of the same name.
lets do some examples:
root@ubuntu16-1:~/test-space# tree
.
├── dir1
│ └── floor1
│ └── floor2
├── dir2
├── dir3
└── file1
​
5 directories, 1 file
copy a file:
root@ubuntu16-1:~/test-space# cp file1 file2
root@ubuntu16-1:~/test-space# ls
dir1 dir2 dir3 file1 file2
take a backup when copying a file
If a copy operation will overwrite a file the -b flag may be used to create a back up of the file. This copies the file into place and writes a backup file.
root@ubuntu16-1:~/test-space# ls
dir1 dir2 dir3 file1 file2
root@ubuntu16-1:~/test-space# echo "this is file2 content" > file2
root@ubuntu16-1:~/test-space# echo "ehis is file1 content" > file1
root@ubuntu16-1:~/test-space# cp -b file1 file2
root@ubuntu16-1:~/test-space# ls
dir1 dir2 dir3 file1 file2 file2~
root@ubuntu16-1:~/test-space# cat file2
ehis is file1 content
root@ubuntu16-1:~/test-space# cat file2~
this is file2 content
specify the name of the backup file use the -S option. try cp -S .file2bak file1 file2
copy multiple files (into a directory)
root@ubuntu16-1:~/test-space# cp file1 file2 dir2/
root@ubuntu16-1:~/test-space# tree
.
├── dir1
│ └── floor1
│ └── floor2
├── dir2
│ ├── file1
│ └── file2
├── dir3
├── file1
├── file2
└── file2~
​
​
5 directories, 4 files
Copying files recursively
We can use cp to copy entire directory structures from one place to another using the -R option to perform a recursive copy.
Let's say you are the user root and you have a directory, /home/test-space, which contains many files and subdirectories. You want to copy all those files, and all the subdirectories (and the files and subdirectories they contain), to a new location, /root/files-backup. You can copy all of them using the command:
cp -R ~/test-space ~/files-backup
  • If the directory files-backup already exists, the directory files will be placed inside.
  • If files-backup does not already exist, it will be created and the contents of the files directory will be placed inside it.
copy a directory
By default the cp command will not copy directories. Attempting to copy a directory results in an error.
root@ubuntu16-1:~/test-space# cp dir2 dir4
cp: omitting directory 'dir2'
To copy a directory pass the -R flag. This will recursively copy a folder and create a copy.
root@ubuntu16-1:~/test-space# cp -R dir1 NewDirectoryA
root@ubuntu16-1:~/test-space# tree
.
├── dir1
│ └── floor1
│ └── floor2
├── dir2
│ ├── file1
│ └── file2
├── dir3
├── file1
├── file2
├── file2~
└── NewDirectoryA
└── floor1
└── floor2
​
8 directories, 5 files
copy multiple directories
To copy multiple directories pass the path of the directories to be copied followed by the destination directory.
root@ubuntu16-1:~/test-space# cp -R dir1 dir2 NewDirectoryB
cp: target 'NewDirectoryB' is not a directory
root@ubuntu16-1:~/test-space# mkdir NewDirectoryB
root@ubuntu16-1:~/test-space# cp -R dir1 dir2 NewDirectoryB
root@ubuntu16-1:~/test-space# tree
.
├── dir1
│ └── floor1
│ └── floor2
├── dir2
│ ├── file1
│ └── file2
├── dir3
├── file1
├── file2
├── file2~
├── NewDirectoryA
│ └── floor1
│ └── floor2
└── NewDirectoryB
├── dir1
│ └── floor1
│ └── floor2
└── dir2
├── file1
└── file2
​
13 directories, 7 files
Now lets take a look at some cp command options:
cp command useful options:
Description
-v,--verbose
Verbose mode; explain what is being done.
--preserve
preserve file attributes (permissions, group and user owernship).By default mode, ownership and timestamps will be preserved.
-i , --interactive
Prompt before overwrite (overrides a previous -n option).
-n , --no-clobber
Do not overwrite an existing file. If -i/--interactive was previously specified, this option overrides it. This option cannot be specified with -b/--backup, because backups are only created when a file would have been overwritten.
-f,--force
If an existing destination file cannot be opened, remove it and try again. This option has no effect if the -n/--no-clobber option is used. However, it applies independently of -i/--interactive; neither option cancels the effect of the other.
cp command has lots of options.Try man cp command for more information.

mv

mv is used to move or rename one or more files or directories. In general, the names we can use follow the same rules as for copying with cp; [If you are moving a file on the same file system, the inode wont change].
  • Rename a file( or directory) name source to destination:
mv [options] source destination
  • Move source file(s) or directory(s) to a directory named destination:
mv [options] source [source2 ...] destination
Same as the previous syntax, but specifying the directory first, and the source file(s)(or directory(s)) last
mv [options] -t destination source [source2 ...]
Lets try mv command:
root@ubuntu16-1:~/test-space# tree -F
.
├── dir1/
├── dir2/
├── file1
Renaming a File or a directory:
root@ubuntu16-1:~/test-space# mv file1 NewFile1
root@ubuntu16-1:~/test-space# mv dir1 dirA
root@ubuntu16-1:~/test-space# tree -F
.
├── dir2/
├── dirA/
├── file2
└── NewFile1
Moving Files into a directory:
root@ubuntu16-1:~/test-space# mv NewFile1 file2 dir3
mv: target 'dir3' is not a directory
root@ubuntu16-1:~/test-space# mkdir dir3
root@ubuntu16-1:~/test-space# mv NewFile1 file2 dir3
root@ubuntu16-1:~/test-space# tree -F
.
├── dir2/
├── dir3/
│ ├── file2
│ └── NewFile1
└── dirA/
​
3 directories, 2 files
Moving a directory into another :
root@ubuntu16-1:~/test-space# mv dir3 dirA
root@ubuntu16-1:~/test-space# tree -F
.
├── dir2/
└── dirA/
└── dir3/
├── file2
└── NewFile1
​
3 directories, 2 files
we could usemv -t dirA dir3 command as well. -t, --target-directoryMove all sources into the directory destination.
usefull mv command options:
mv command options
description
-v
verbose - print source and destination files
-i
interactive prompt before overwrite
-u
update - move when source is newer than destination
-f
force move by overwriting destination file without prompt

cp vs mv :

Normally, the cp command will copy a file over an existing copy, if the existing file is writable. On the other hand, the mv will not move or rename a file if the target exists. We can overcome this using the-fswitch.

rm

rm stands for remove here. rm removes files or directories.
rm [OPTION]... FILE...
Lets try:
root@ubuntu16-1:~/test-space# tree -F
.
├── dir1/
├── dir2/
│ └── MyFile
└── file1
​
2 directories, 2 files
Removing Files
root@ubuntu16-1:~/test-space# rm file1
root@ubuntu16-1:~/test-space# tree -F
.
├── dir1/
└── dir2/
└── MyFile
​
2 directories, 1 file
File names starting with a dash, How to remove it?
To remove a file whose name begins with a dash ("-"), you can specify a double dash ("--") separately before the file name. This extra dash is necessary so that rm does not misinterpret the file name as an option: rm -- -file.txtOr, we can delete it by referring to it with a pathname : rm /home/hope/-file.txt
some other options of rm command:
mv options
description
-v
Verbose mode; explain at all times what is being done.
-i
prompt before every removal
-f,--force
Ignore none existant files,and never prompt before removing.
-d,--dir
Remove empty directories.

Removing directories

root@ubuntu16-1:~/test-space# rm dir1
rm: cannot remove 'dir1': Is a directory
By default, rm does not remove directories.
If the specified directory is empty, it may be removed with the -d/--dir option, instead.
root@ubuntu16-1:~/test-space# rm -d dir1
root@ubuntu16-1:~/test-space# tree -F
.
└── dir2/
└── MyFile
​
1 directory, 1 file
What if desired directory contains some files? If the -r/-R/--recursive option is specified, we can remove that directory however rm will remove any matching directories and their contents!
root@ubuntu16-1:~/test-space# rm -rf dir2
root@ubuntu16-1:~/test-space# tree -F
.
​
0 directories, 0 files
rm -dlets us to remove a directory without specifying -r/-R/--recursive, provided that the directory is empty. In other words, rm -d is equivalent to using rmdir.

rmdir

Removing directories using the rmdir command is the opposite of creating them. We can remove a directory with rmdir only if it is empty as there is no option to force removal.
rmdir [options] directory ...
Again, there is a-p option to remove parents as well. Let try it:
root@ubuntu16-1:~/test-space# tree -F
.
├── dir1/
│ └── file1
├── dir2/
└── dir3/
└── dirA/
└── dirB/
​
5 directories, 1 file
root@ubuntu16-1:~/test-space# rmdir dir1
rmdir: failed to remove 'dir1': Directory not empty
root@ubuntu16-1:~/test-space# rmdir dir2
root@ubuntu16-1:~/test-space# tree -F
.
├── dir1/
│ └── file1
└── dir3/
└── dirA/
└── dirB/
​
4 directories, 1 file
root@ubuntu16-1:~/test-space# rmdir -p dir3/dirA/
root@ubuntu16-1:~/test-space# rmdir -p dir3/dirA/dirB/
root@ubuntu16-1:~/test-space# tree -F
.
└── dir1/
└── file1
​
1 directory, 1 file
Normally, whenrmdir is instructed to remove a non-empty directory, it reports an error. With --ignore-fail-on-non-emptyoption suppresses those error messages.

Handling multiple files and directories

Some time we need to work on more than one files, Now we try to have review over some recursive commands

Recursive manipulation

Recursive listing
The ls command has a -R (note uppercase “R”) option for listing a directory and all its subdirectories. The recursive option applies only to directory names, for example, in a directory tree.
root@ubuntu16-1:~/test-space# tree
.
├── dir1
│ └── text1
├── dir2
├── file1
└── file2
​
2 directories, 3 files
root@ubuntu16-1:~/test-space# ls -R
.:
dir1 dir2 file1 file2
​
./dir1:
text1
​
./dir2:
Recursive copy
We can use the -r (or -R or --recursive) option to cause the cp command to descend into source directories and copy the contents recursively. To prevent an infinite recursion, we cannot copy the source directory itself!
root@ubuntu16-1:~# cp -R test-space NewCopy
root@ubuntu16-1:~# tree NewCopy/
NewCopy/
├── dir1
│ └── text1
├── dir2
├── file1
└── file2
​
2 directories, 3 files
Recursive deletion
I mentioned earlier that rmdir only removes empty directories. We can use the -r (or -R or --recursive) option to cause the rm command to remove both files and directories:
root@ubuntu16-1:~# ls
client.conf NewCopy unzip_6.0-20ubuntu1_amd64.deb
files-backup openvpn.key zip_3.0-11_amd64.deb
jcal_0.4.1-2_amd64.deb test-space
root@ubuntu16-1:~# rm -rf NewCopy/
root@ubuntu16-1:~# ls
client.conf openvpn.key zip_3.0-11_amd64.deb
files-backup test-space
jcal_0.4.1-2_amd64.deb unzip_6.0-20ubuntu1_amd64.deb

Wildcards and Globbing

File globbing is a feature provided by the UNIX/Linux shell to represent multiple filenames by using special characters called wildcards with a single file name. A wildcard is essentially a symbol which may be used to substitute for one or more characters. Therefore, we can use wildcards for generating the appropriate combination of file names as per our requirement.
root@ubuntu16-1:~/test-space# ls -l
total 0
-rw-r--r-- 1 root root 0 Sep 28 00:26 aaa.txt
-rw-r--r-- 1 root root 0 Sep 28 00:27 ababa.txt
-rw-r--r-- 1 root root 0 Sep 28 00:26 bbbb.txt
-rw-r--r-- 1 root root 0 Sep 27 23:33 file1
-rw-r--r-- 1 root root 0 Sep 27 23:33 file2
  • ? is used to match any single character. We can use ‘?’ for multiple times for matching multiple characters.
root@ubuntu16-1:~/test-space# ls ???.txt
aaa.txt
  • * is used to match zero or more characters. If we have less information to search any file or information then we can use ‘*’ in globbing pattern.
root@ubuntu16-1:~/test-space# ls *.txt
aaa.txt ababa.txt bbbb.txt
  • [ ]is used to match the character from the range. Some of the mostly used range declarations are mentioned below:
[A-Z] : All uppercase alphabets
[a-z] : All lowercase alphabets
[a-zA-Z0-9] : All uppercase alphabets, lowercase alphabet and digits
The-character between two others represents a range that includes the two other characters and all characters between them in the collating sequence.
root@ubuntu16-1:~/test-space# ls [e-z]*
file1 file2
  • The! character means NOT so it matches any character except the remaining characters.
root@ubuntu16-1:~/test-space# ls [!e-z]*
aaa.txt ababa.txt bbbb.txt
  • { }can be used to match filenames with more than one globbing patterns. Each pattern is separated by ‘,’ in curly bracket without any space.
root@ubuntu16-1:~/test-space# ls {???.txt,????.txt}
aaa.txt bbbb.txt
rm {*.doc,*.docx} : delete all files whose extensions are ‘doc’ or ‘docx’.
  • and finally \ is used as an "escape" character, we have used it to protect a subsequent special character. example: "\\” searches for a backslash
We can disable globbing using set -f command.
Wildcard patterns vs Regular Expressions
Wildcard patterns and regular expression patterns share some characteristics, but they are not the same. Pay careful attention.
Now that we’ve covered the file and directory topic with the big recursive hammer that hits everything, and the globbing hammer that hits more selectively, let’s look at the find command, which can be more like a surgeon’s knife.

Finding Files

The find command is used to find files in one or more directory trees, based on criteria such as name, time stamp, or size.

find

The find command searches for files or directories using all or part of the name, or by other search criteria, such as size, type, file owner, creation date, or last access date.
find starting/path options expression
  1. 1.
    The starting/path attribute will define the top level directory where find begins filtering.
  2. 2.
    The optionsattribute will control the behavior and optimization method of the find process.
  3. 3.
    The expression attribute controls the tests that search the directory hierarchy to produce output.
    The most basic find is a search by name or part of a name:
root@ubuntu16-1:~/test-space# find /etc/ -iname "[y-z]*"
/etc/xdg/autostart/zeitgeist-datahub.desktop
/etc/zsh_command_not_found
/etc/vmware-tools/messages/zh_TW
/etc/vmware-tools/messages/zh_CN
/etc/dhcp/dhclient-exit-hooks.d/zzz_avahi-autoipd
/etc/kernel/postrm.d/zz-update-grub
/etc/kernel/postinst.d/zz-update-grub
/etc/brltty/Contraction/zu.ctb
/etc/brltty/Contraction/zh-tw-ucb.ctb
/etc/brltty/Contraction/zh-tw.ctb
-name option used for searching for files based on their name. -imakes it case insensitive. In the first example above, we found both files and a directory (/etc).
finding hidden files : If you want to find a file or directory whose name begins with a dot, such as .bashrc or the current directory (.), then you must specify a leading dot as part of the pattern. Otherwise, name searches ignore these files or directories. find . -name ".*"
note: If you want to chain different results together, you can use the “-and” or “-or” commands. The “-and” is assumed if omitted. find . -name file1 -or -name file9
Finding files by type
We can specify the type of files you want to find with the “-type” parameter. It works like this:
find -type type_descriptor query
  • -type fwill search for a regular file
  • -type d will search for a directory
  • -type l will search for a symbolic link
root@ubuntu16-1:~/test-space# find /etc/ -type f -iname "[y-z]*"
/etc/xdg/autostart/zeitgeist-datahub.desktop
/etc/zsh_command_not_found
/etc/dhcp/dhclient-exit-hooks.d/zzz_avahi-autoipd
/etc/kernel/postrm.d/zz-update-grub
/etc/kernel/postinst.d/zz-update-grub
/etc/brltty/Contraction/zu.ctb
/etc/brltty/Contraction/zh-tw-ucb.ctb
/etc/brltty/Contraction/zh-tw.ctb
Finding files by size
We can also search by file size, either for a specific size (n) or for files that are either larger (+n) or smaller than a given value (-n). By using both upper and lower size bounds, we can find files whose size is within a given range. By default, the -size option of find assumes a unit of ‘b’ for 512-byte blocks.
  • -size +/- [b] [c] [w] [k] [M} [G]
b for 512-byte blocks (this is the default if no suffix is used)
c for bytes
w for two-byte words
k for Kilobytes (units of 1024 bytes)
M for Megabytes (units of 1048576 bytes)
G for Gigabytes (units of 1073741824 bytes)
as an example lets find files smaller than 1 kilobytes:
root@ubuntu16-1:~/test-space# find /etc/ -type f -size -1k
/etc/dictionaries-common/ispell-default
/etc/cups/printers.conf
/etc/vmware-caf/pme/config/_previous_/cafenv.config
/etc/.pwd.lock
/etc/apt/trusted.gpg.d/peek-developers_ubuntu_stable.gpg~
/etc/security/opasswd
/etc/gconf/gconf.xml.defaults/%gconf-tree.xml
/etc/gconf/gconf.xml.mandatory/%gconf-tree.xml
/etc/sensors.d/.placeholder
/etc/newt/palette.original
We can find all empty files using find . -size 0b or find . -empty .
Finding files based on their time:
Linux stores time data about access times, modification times, and change times.
  • Access Time: Last time a file was read or written to.
  • Modification Time: Last time the contents of the file were modified.
  • Change Time: Last time the file’s inode meta-data was changed.
We can use the time stamps described with the touch command to locate files having particular time stamps.
-amin n: The file was last accessed n minutes ago
-anewer: The file was last accessed more recently than it was modified
-atime n: The file was last accessed more n days ago
-cmin n: The file was last changed n minutes ago
-cnewer: The file was last changed more recently than the file was modified
-ctime n: The file was last changed more than n days ago
-mmin n: File's data was last modified n minutes ago
-mtime n: File's data was last modified n days ago
again (+/-) signs can be used to give it a range.
Find Changed Files in Last 2 Hours:
root@ubuntu16-1:~/test-space# find /home -cmin -120
/home/user1/.cache/upstart
/home/user1/.cache/upstart/indicator-printers.log
/home/user1/.cache/upstart/unity-panel-service.log
note : Adding the -daystart option to -mtime or -atime means that we want to consider days as calendar days, starting at midnight. So to list the regular files in your home directory that were modified yesterday we can use find ~/ -daystart -type f -mtime 1 .
We can also find files by owner and permissions and use filter result by depth (will be discussed in later sections"104-7")
Acting on files with two other switches:
find command switch
meaning
-ls
list current file in ls -dils format on standard output
-print
print the full file name on the standard output
As you can see find command has tons of options, get into more details using man page files.

Executing and Combining Find Commands (-exec)

We can execute an arbitrary helper command on everything that find matches by using the “-exec” parameter. This is called like this:
find find_parameters -exec command_and_params {} \;
The {} is used as a placeholder for the files that find matches. The “\;” is used so that find knows where the command ends.
As an instance this will remove all empty files:
find . -empty -exec rm {} \;
We could remove all empty files in this directory and its subdirectories:
find . -empty -exec rm '{}' \;
We could then change the directory permissions like this:
find . -name "*.deb" -exec cp {} /tmp/packages \;

Identifying files

File names often have a suffix such as gif, jpeg, or html that gives a hint of what the file might contain. Linux does not require such suffixes and generally does not use them to identify a file type. Knowing what type of file you are dealing with helps you know what program to use to display or manipulate it.

file

The file command tells us something about the type of data in one or more files.
file [option] [filename]
root@ubuntu16-1:~/test-space# ls -l
total 10880
-rwxrw-rw- 1 user1 user1 10819475 Mar 29 2015 01 - Intro.mp4
-rw------- 1 user1 user1 221941 Sep 1 00:24 zabbix-cli-manual-1.7.0.pdf
-rw------- 1 user1 user1 91087 Aug 31 00:40 zabbix-cli-rpm-2.1.1-1.tar.gz
​
root@ubuntu16-1:~/test-space# file 01\ -\ Intro.mp4
01 - Intro.mp4: ISO Media, MP4 Base Media v1 [IS0 14496-12:2003]
-b, –brief : This is used to display just file type in brief mode.
root@ubuntu16-1:~/test-space# file -b zabbix-cli-manual-1.7.0.pdf
PDF document, version 1.4
-z: Try to look inside compressed files.
root@ubuntu16-1:~/test-space# file -z zabbix-cli-rpm-2.1.1-1.tar.gz zabbix-cli-rpm-2.1.1-1.tar.gz:
POSIX tar archive (gzip compressed data, from Unix)
and -ioption To view mime type of file.
A MIME type is a label used to identify a type of data. It is used so software can know how to handle the data. It serves the same purpose on the Internet that file extensions do on Microsoft Windows.

Archiving and Compressing files

Archiving and compressing are two different things
  • tar just archive files and does not do any compression by default.
  • zip does both archiving and compresion.
  • gzip and bzip2 are used just for compression.

zip

Zip is one of the most popular archive file format out there. With zip, you can compress multiple files into one file. This not only saves disk space, it also saves network bandwidth. This is why you’ll encounter zip files almost all the time.
zip options archive inpath inpath ...
Lets take a look a look:
root@ubuntu16-1:~/test-space/myfiles# tree -F
.
├── dir1/
│   └── myvideo.mp4*
├── dir2/
│   ├── zabbix-cli-manual-1.7.0.pdf
│   └── zabbix-cli-rpm-2.1.1-1.tar.gz
├── myconf.txt
└── mylog.txt
​
2 directories, 5 files
​
root@ubuntu16-1:~/test-space/myfiles# zip myconf.zip myconf.txt
adding: myconf.txt (deflated 60%)
​
root@ubuntu16-1:~/test-space/myfiles# tree -F
.
├── dir1/
│   └── myvideo.mp4*
├── dir2/
│   ├── zabbix-cli-manual-1.7.0.pdf
│   └── zabbix-cli-rpm-2.1.1-1.tar.gz
├── myconf.txt
├── myconf.zip
└── mylog.txt
​
2 directories, 6 files
use the -r option with the zip command and it will recursively zips the files in a directory. This option helps you to zip all the files present in the specified directory:
root@ubuntu16-1:~/test-space/myfiles# cd ..
root@ubuntu16-1:~/test-space# zip -r myfiles.zip myfiles/
adding: myfiles/ (stored 0%)