Iman Mahdavi Doost

  1-02-2021

 0

Follow

Share post:

103.3 Perform basic file management

Weight: 4

Candidates should be able to use the basic Linux commands to manage files and directories.

Objectives

• 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.

• cp
• find
• mkdir
• mv
• ls
• rm
• rmdir
• touch
• tar
• cpio
• dd
• file
• gzip
• gunzip
• bzip2
• file globbing

ls

Is used to list directories & files. It can use absolute and relative paths

$ ls -l
total 52
-rw-rw-r-- 1 jadi jadi  146 Jan  5 08:29 alldata
-rw-rw-r-- 1 jadi jadi   30 Jan  5 09:15 howcool.sort
-rw-rw-r-- 1 jadi jadi  204 Jan  5 08:49 mydata
-rw-rw-r-- 1 jadi jadi  121 Jan  4 22:07 mydata.tab
drwxrwxr-x 2 jadi jadi 4096 Jan  8 16:45 mydir
-rw-rw-r-- 1 jadi jadi   70 Jan  5 08:28 myfiles
drwxrwxr-x 2 jadi jadi 4096 Jan  8 16:46 newdir
-rw-rw-r-- 1 jadi jadi   23 Jan  5 09:06 sorttest.txt
-rw-rw-r-- 1 jadi jadi   58 Jan  5 09:14 uses

First field indicates if this is a file (-) or directory (d).

• -l is for long (more info for each file)
• -1 will print one file per line
• -t sorts based on modification date
• -r reverses the search (so -tr is reverse time (newer files at the bottom).

you can always mix switches. A famous one is -ltrh (long+human readable sizes+reverse time).

Copying, Moving & Deleting

cp

This will copy files from one place / name to another place / name. If the target is a directory, all sources will be copied there.

cp source destination

mv

Will move or rename files or directories. It works like cp command. If you are moving a file on the same file system, the inode wont change.

In general:

• 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.

But use common sense when answering questions or using cp and mv in real life.

rm

Removes (Deletes) files.

General notes

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. You can overcome this using the -f switch.

• -f (--force) will cause cp to try overwrite the target.
• -i (--interactive) will ask Y/N question (deleting / overwriting).
• -b (--backup) will make backups of overwritten files
• -p will preserve the attributes.

Creating and removing directories

The mkdir command creates directories.

$ ls
howcool.sort  uses.sort
$ mkdir dirA dirB
$ ls -ltrh 
total 16K
-rw-rw-r-- 1 jadi jadi   30 Jan  8 16:45 howcool.sort
-rw-rw-r-- 1 jadi jadi   58 Jan  8 16:45 uses.sort
drwxrwxr-x 2 jadi jadi 4.0K Jan  8 17:11 dirB
drwxrwxr-x 2 jadi jadi 4.0K Jan  8 17:11 dirA

• -p will create nested directories:

$ mkdir newDir/insideNew/lastDir
mkdir: cannot create directory ‘newDir/insideNew/lastDir’: No such file or directory
$ mkdir -p newDir/insideNew/lastDir
$ ls newDir/insideNew/ -ltrh
total 4.0K
drwxrwxr-x 2 jadi jadi 4.0K Jan  8 17:13 lastDir

If you need to delete a directory the command is rmdir and you can also use the -p for nested removing:

$ tree
.
├── dirA
├── dirB
├── howcool.sort
└── uses.sort

2 directories, 2 files
$ rmdir dirA dirB
$ mkdir -p newDir/insideNew/lastDir
$ tree
.
├── howcool.sort
├── newDir
│   └── insideNew
│       └── lastDir
└── uses.sort

3 directories, 2 files
$ rmdir -p newDir/insideNew/lastDir
$ tree
.
├── howcool.sort
└── uses.sort

0 directories, 2 files

If you are using rmdir to remove a directory, it MUST BE EMPTY! although later we will see how you can erase directories using rm command.

Handling multiple files at once

Most of the times we need to work with more than one file. This is Linux and there are ways!

Recursive commands

Recursive means going inside and inside and inside and inside! In many commands -r or -R is dedicated to recursive commands. Say ls. It uses -R :

$ ls
howcool.sort  newDir  uses.sort
$ ls -R
.:
howcool.sort  newDir  uses.sort

./newDir:
insideNew  TestFile

./newDir/insideNew:
lastDir

./newDir/insideNew/lastDir:

It is more useful when you are copying or deleting. When using cp or rm, -r (or -R or --recursive) will copy/delete all files inside the given source.

$ tree mydir
mydir
├── howcool.sort
├── newDir
│   ├── insideNew
│   │   └── lastDir
│   └── TestFile
└── uses.sort

3 directories, 3 files
$ mkdir newCopy
$ cp mydir newCopy
cp: omitting directory ‘mydir’
$ cp -r mydir newCopy
$ tree newCopy/
newCopy/
└── mydir
    ├── howcool.sort
    ├── newDir
    │   ├── insideNew
    │   │   └── lastDir
    │   └── TestFile
    └── uses.sort

4 directories, 3 files

Same works with rm:

$ rm newCopy
rm: cannot remove ‘newCopy’: Is a directory
$ rm -r newCopy

As you can see we can not rm a file but if using -r (or -R or --recursive) it works because it deletes the dir and whatever inside it.

rm -rf / is EXTREMELY DANGEROUS: force delete whatever in /

Wildcards and globbing

This is a way to say All files or everything which starts with A or all files with 3 letter names which end in A or B or C.

There are main cases:

• * means any string
• ? means any single character
• [ABC] matches A, B & C
• [a-k] matches a, b, c, ..., k (both lower-case and capital)
• [0-9a-z] matches all digits and numbers
• [!x] means NOT X.

So... this means that you can use these patterns in your commands to point to these files:

touch

The touch command with no option will update the modification date of a file to the current time (will create a file if it is not exists).

/touch$ ls -l
total 0
-rw-rw-r-- 1 jadi jadi 0 Jan  8 17:47 myfile
/touch$ touch myfile  #after a minute
/touch$ ls -l
total 0
-rw-rw-r-- 1 jadi jadi 0 Jan  8 17:48 myfile

There are also possible:

[ian@echidna lpi103-2]$ touch -t 200908121510.59 f3
[ian@echidna lpi103-2]$ touch -d 11am f4
[ian@echidna lpi103-2]$ touch -d "last fortnight" f5
[ian@echidna lpi103-2]$ touch -d "yesterday 6am" f6
[ian@echidna lpi103-2]$ touch -d "2 days ago 12:00" f7
[ian@echidna lpi103-2]$ touch -d "tomorrow 02:00" f8
[ian@echidna lpi103-2]$ touch -d "5 Nov" f9
[ian@echidna lpi103-2]$ ls -lrt f*
-rw-rw-r--. 1 ian ian 0 2009-07-31 18:31 f5
-rw-rw-r--. 1 ian ian 0 2009-08-12 12:00 f7
-rw-rw-r--. 1 ian ian 0 2009-08-12 15:10 f3
-rw-rw-r--. 1 ian ian 0 2009-08-13 06:00 f6
-rw-rw-r--. 1 ian ian 0 2009-08-14 11:00 f4
-rw-rw-r--. 1 ian ian 4 2009-08-14 18:25 f1
-rw-rw-r--. 1 ian ian 0 2009-08-14 18:27 f2
-rw-rw-r--. 1 ian ian 0 2009-08-15 02:00 f8
-rw-rw-r--. 1 ian ian 0 2009-11-05 00:00 f9

and the most advanced way is setting time of a file based on another file:

[ian@echidna lpi103-2]$ date
Fri Aug 14 18:33:48 EDT 2009
[ian@echidna lpi103-2]$ date -r f1
Fri Aug 14 18:25:50 EDT 2009
[ian@echidna lpi103-2]$ touch -r f1 f1a
[ian@echidna lpi103-2]$ ls -l f1*
-rw-rw-r--. 1 ian ian 4 2009-08-14 18:25 f1
-rw-rw-r--. 1 ian ian 0 2009-08-14 18:25 f1a

Finding files

The find command helps us to find files based on MANY criteria. Look at this:

$ find . -iname "[a-j]*"
./howcool.sort
./alldata
./mydir/howcool.sort
./mydir/newDir/insideNew
./howcool

• the first parameter says where should be searched (with subdirectories).
• the -name switch indicates the criteria (here iname: searching for files with this name).

a common switch is -iname which says "name but case is not important (z is same as Z)". Also -d is commonly used:

$ find . -iname "*my*" 
./myfiles
./mydata.noenter
./mydata
./mydir
./mydir/hereisMYfile.txt
./touch/myfile
./mydata.tab
$ find . -type f -iname "*my*" 
./myfiles
./mydata.noenter
./mydata
./mydir/hereisMYfile.txt
./touch/myfile
./mydata.tab

These are the most common file types:

• -type f will search for a regular file
• -type d will search for a directory
• -type l will search for a symbolic link

you can also search for file sizes:

So this will find all files ending in tmp with size between 1M and 100M in /var/ directory:

find /var -iname '*tmp* -size +1M -size -100M

you can find all empty files with find . -size 0b or find . -empty

Acting on files

We can act on files with various switches:

But the best way to run commands on found files is -exec switch. You can point to the file with '{}' or {} and finish your command with ;.

This will remove all empty files in this directory and its subdirectories:

find . -empty -exec rm '{}' ;

or this will rename all htm files to hfml

find . -name "*.htm" -exec mv '{}' '{}l' ;

At last you have to know the -mtime switch for finding files based on their time.

if you add -daystart switch to -mtime or -atime it means that we want to consider days as calendar days, starting at midnight.

Identify a file

That is the file command:

$ file mydata.tab 
mydata.tab: ASCII text
$ file /bin/bash 
/bin/bash: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.32, BuildID[sha1]=cb63ec0718f2022619814c04a5b6cd8a36752a83, stripped
$ file mydata.tab 
mydata.tab: ASCII text
$ file /bin/bash 
/bin/bash: ELF 64-bit LSB executable, x86-64, version 1 (SYSV), dynamically linked (uses shared libs), for GNU/Linux 2.6.32, BuildID[sha1]=cb63ec0718f2022619814c04a5b6cd8a36752a83, stripped
$ file -i mydir
mydir: inode/directory; charset=binary

-i switch prints the complete mime format

Compressing files

Compressing works best on text files.

zip

we mostly use gzip and gunzip in linux. It is very easy:

$ ls *  -ltrh 
-rw-r--r-- 1 jadi jadi  79K Dec 22 11:52 The.Equalizer.2014.1080p.BluRay.x264.anoXmous_eng.srt
$ gzip  The.Equalizer.2014.1080p.BluRay.x264.anoXmous_eng.srt 
$ ls *  -ltrh 
-rw-r--r-- 1 jadi jadi  30K Dec 22 11:52 The.Equalizer.2014.1080p.BluRay.x264.anoXmous_eng.srt.gz
$ gunzip The.Equalizer.2014.1080p.BluRay.x264.anoXmous_eng.srt.gz 
$ ls *  -ltrh 
-rw-r--r-- 1 jadi jadi  79K Dec 22 11:52 The.Equalizer.2014.1080p.BluRay.x264.anoXmous_eng.srt

• gzip preserves time
• gzip creates the new compressed file with the same name but with .gz ending
• gzip removes the original files after creating the compressed file

bzip2

is another compressing tool. Works just the same but with another compression algorithm.

$ ls *  -ltrh 
-rw-r--r-- 1 jadi jadi  79K Dec 22 11:52 The.Equalizer.2014.1080p.BluRay.x264.anoXmous_eng.srt
$ bzip2 The.Equalizer.2014.1080p.BluRay.x264.anoXmous_eng.srt 
$ ls *  -ltrh 
-rw-r--r-- 1 jadi jadi  22K Dec 22 11:52 The.Equalizer.2014.1080p.BluRay.x264.anoXmous_eng.srt.bz2
$ bunzip2 The.Equalizer.2014.1080p.BluRay.x264.anoXmous_eng.srt.bz2 
$ ls *  -ltrh 
-rw-r--r-- 1 jadi jadi  79K Dec 22 11:52 The.Equalizer.2014.1080p.BluRay.x264.anoXmous_eng.srt

Archiving files

Sometimes we need to create an archive file from many files for easier moving or backing up. This is done with cpio and tar.

tar

TapeARchive or tar is the most common archiving tool. In automatically create an archive file from a directory and all its subdirs.

Common switches are

If you issue absolute paths, tar removes the starting slash (/) for safety reasons when creating an archive. If you want to override, use -p option.

tar can work with tapes and other storages. Thats why we use -f to tell it that we are working with files.

cpio

Gets a list of files and creates archive (one file) of it which can be opened later.

$ ls | cpio -o > allfilesls.cpio
3090354 blocks

• -o makes cpio to create an output from its input
• cpio does not goes into the folders. So mostly we use it with find:

find . -name "*" | cpio -o > myarchivefind.cpio

to decompress it:

mkdir extract
mv myarchivefind.cpio extract
cd extract
cpio -id < myarchivefind.cpio

• -d will create the folders
• -i is for extract

dd

The dd command copies data from one location to another. This data comes from files. You can use it just like copy:

$ cat howcool
jadi    5
sina    6
rubic    2
you     12
$ dd if=howcool of=newcool
0+1 records in
0+1 records out
30 bytes (30 B) copied, 0.0227904 s, 1.3 kB/s
$ cat newcool 
jadi    5
sina    6
rubic    2
you     12
$

• if is In File
• of is Out File

But it is used in many other cases specially writing directly to block devices such as /dev/sdb or changing data to upper/lower case.

This will backup my whole hard to a file:

# dd if=/dev/sda of=backup.dd bs=4096

or better:

# dd if=/dev/sda2 |gzip >backup.dd.gzip

Another common usage is creating files of specific size:

$ dd if=/dev/zero of=1g.bin bs=1G count=1

.

No Comments Yet...

Related Articles

Linux

104.5 Manage file permissions and ownership

byIman Mahdavi Doost

 0   1-02-2021

Linux

104.3. Control mounting and unmounting of filesystems

byIman Mahdavi Doost

 0   1-02-2021

Linux

104.2 Maintain the integrity of filesystems

byIman Mahdavi Doost

 0   1-02-2021

Linux

104.1. Create partitions and filesystems

byIman Mahdavi Doost

 0   1-02-2021

Linux

103.8 Perform basic file editing operations using vi

byIman Mahdavi Doost

 0   1-02-2021

Linux

103.7 Search text files using regular expressions

byIman Mahdavi Doost

 0   1-02-2021

Linux

102.5 Use RPM and YUM package management

byIman Mahdavi Doost

 0   1-02-2021

Linux

102.4. Use Debian package management

byIman Mahdavi Doost

 0   1-02-2021