Chapter 9. working with files

Chapter 9. working with files
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In this chapter we learn how to recognise, create, remove, copy and move files using commands like file, touch, rm, cp, mv and rename.

all files are case sensitive

Files on Linux (or any Unix) are case sensitive. This means that FILE1 is different from file1, and /etc/hosts is different from /etc/Hosts (the latter one does not exist on a typical Linux computer).

This screenshot shows the difference between two files, one with upper case W, the other with lower case w.

paul@laika:~/Linux$ ls
winter.txt  Winter.txt
paul@laika:~/Linux$ cat winter.txt
It is cold.
paul@laika:~/Linux$ cat Winter.txt
It is very cold!

everything is a file

A directory is a special kind of file, but it is still a (case sensitive!) file. Each terminal window (for example /dev/pts/4), any hard disk or partition (for example /dev/sdb1) and any process are all represented somewhere in the file system as a file. It will become clear throughout this course that everything on Linux is a file.

file

The file utility determines the file type. Linux does not use extensions to determine the file type. The command line does not care whether a file ends in .txt or .pdf. As a system administrator, you should use the file command to determine the file type. Here are some examples on a typical Linux system.

paul@laika:~$ file pic33.png
pic33.png: PNG image data, 3840 x 1200, 8-bit/color RGBA, non-interlaced
paul@laika:~$ file /etc/passwd
/etc/passwd: ASCII text
paul@laika:~$ file HelloWorld.c
HelloWorld.c: ASCII C program text

The file command uses a magic file that contains patterns to recognise file types. The magic file is located in /usr/share/file/magic. Type man 5 magic for more information.

It is interesting to point out file -s for special files like those in /dev and /proc.

root@debian6~# file /dev/sda
/dev/sda: block special
root@debian6~# file -s /dev/sda
/dev/sda: x86 boot sector; partition 1: ID=0x83, active, starthead...
root@debian6~# file /proc/cpuinfo 
/proc/cpuinfo: empty
root@debian6~# file -s /proc/cpuinfo
/proc/cpuinfo: ASCII C++ program text

touch

create an empty file

One easy way to create an empty file is with touch. (We will see many other ways for creating files later in this book.)

This screenshot starts with an empty directory, creates two files with touch and the lists those files.

paul@debian7:~$ ls -l
total 0
paul@debian7:~$ touch file42
paul@debian7:~$ touch file33
paul@debian7:~$ ls -l
total 0
-rw-r--r-- 1 paul paul 0 Oct 15 08:57 file33
-rw-r--r-- 1 paul paul 0 Oct 15 08:56 file42
paul@debian7:~$

touch -t

The touch command can set some properties while creating empty files. Can you determine what is set by looking at the next screenshot? If not, check the manual for touch.

paul@debian7:~$ touch -t 200505050000 SinkoDeMayo
paul@debian7:~$ touch -t 130207111630 BigBattle.txt
paul@debian7:~$ ls -l
total 0
-rw-r--r-- 1 paul paul 0 Jul 11  1302 BigBattle.txt
-rw-r--r-- 1 paul paul 0 Oct 15 08:57 file33
-rw-r--r-- 1 paul paul 0 Oct 15 08:56 file42
-rw-r--r-- 1 paul paul 0 May  5  2005 SinkoDeMayo
paul@debian7:~$

rm

remove forever

When you no longer need a file, use rm to remove it. Unlike some graphical user interfaces, the command line in general does not have a waste bin or trash can to recover files. When you use rm to remove a file, the file is gone. Therefore, be careful when removing files!

paul@debian7:~$ ls
BigBattle.txt  file33  file42  SinkoDeMayo
paul@debian7:~$ rm BigBattle.txt
paul@debian7:~$ ls
file33  file42  SinkoDeMayo
paul@debian7:~$

rm -i

To prevent yourself from accidentally removing a file, you can type rm -i.

paul@debian7:~$ ls
file33  file42  SinkoDeMayo
paul@debian7:~$ rm -i file33
rm: remove regular empty file `file33'? yes
paul@debian7:~$ rm -i SinkoDeMayo
rm: remove regular empty file `SinkoDeMayo'? n
paul@debian7:~$ ls
file42  SinkoDeMayo
paul@debian7:~$

rm -rf

By default, rm -r will not remove non-empty directories. However rm accepts several options that will allow you to remove any directory. The rm -rf statement is famous because it will erase anything (providing that you have the permissions to do so). When you are logged on as root, be very careful with rm -rf (the f means force and the r means recursive) since being root implies that permissions don't apply to you. You can literally erase your entire file system by accident.

paul@debian7:~$ mkdir test
paul@debian7:~$ rm test
rm: cannot remove `test': Is a directory
paul@debian7:~$ rm -rf test
paul@debian7:~$ ls test
ls: cannot access test: No such file or directory
paul@debian7:~$

cp

copy one file

To copy a file, use cp with a source and a target argument.

paul@debian7:~$ ls
file42  SinkoDeMayo
paul@debian7:~$ cp file42 file42.copy
paul@debian7:~$ ls
file42  file42.copy  SinkoDeMayo

copy to another directory

If the target is a directory, then the source files are copied to that target directory.

paul@debian7:~$ mkdir dir42
paul@debian7:~$ cp SinkoDeMayo dir42
paul@debian7:~$ ls dir42/
SinkoDeMayo

cp -r

To copy complete directories, use cp -r (the -r option forces recursive copying of all files in all subdirectories).

paul@debian7:~$ ls
dir42  file42  file42.copy  SinkoDeMayo
paul@debian7:~$ cp -r dir42/ dir33
paul@debian7:~$ ls
dir33  dir42  file42  file42.copy  SinkoDeMayo
paul@debian7:~$ ls dir33/
SinkoDeMayo

copy multiple files to directory

You can also use cp to copy multiple files into a directory. In this case, the last argument (a.k.a. the target) must be a directory.

paul@debian7:~$ cp file42 file42.copy SinkoDeMayo dir42/
paul@debian7:~$ ls dir42/
file42  file42.copy  SinkoDeMayo

cp -i

To prevent cp from overwriting existing files, use the -i (for interactive) option.

paul@debian7:~$ cp SinkoDeMayo file42
paul@debian7:~$ cp SinkoDeMayo file42
paul@debian7:~$ cp -i SinkoDeMayo file42
cp: overwrite `file42'? n
paul@debian7:~$

mv

rename files with mv

Use mv to rename a file or to move the file to another directory.

paul@debian7:~$ ls
dir33  dir42  file42  file42.copy  SinkoDeMayo
paul@debian7:~$ mv file42 file33
paul@debian7:~$ ls
dir33  dir42  file33  file42.copy  SinkoDeMayo
paul@debian7:~$

When you need to rename only one file then mv is the preferred command to use.

rename directories with mv

The same mv command can be used to rename directories.

paul@debian7:~$ ls -l
total 8
drwxr-xr-x 2 paul paul 4096 Oct 15 09:36 dir33
drwxr-xr-x 2 paul paul 4096 Oct 15 09:36 dir42
-rw-r--r-- 1 paul paul    0 Oct 15 09:38 file33
-rw-r--r-- 1 paul paul    0 Oct 15 09:16 file42.copy
-rw-r--r-- 1 paul paul    0 May  5  2005 SinkoDeMayo
paul@debian7:~$ mv dir33 backup
paul@debian7:~$ ls -l
total 8
drwxr-xr-x 2 paul paul 4096 Oct 15 09:36 backup
drwxr-xr-x 2 paul paul 4096 Oct 15 09:36 dir42
-rw-r--r-- 1 paul paul    0 Oct 15 09:38 file33
-rw-r--r-- 1 paul paul    0 Oct 15 09:16 file42.copy
-rw-r--r-- 1 paul paul    0 May  5  2005 SinkoDeMayo
paul@debian7:~$

mv -i

The mv also has a -i switch similar to cp and rm.

this screenshot shows that mv -i will ask permission to overwrite an existing file.

paul@debian7:~$ mv -i file33 SinkoDeMayo
mv: overwrite `SinkoDeMayo'? no
paul@debian7:~$

rename

about rename

The rename command is one of the rare occasions where the Linux Fundamentals book has to make a distinction between Linux distributions. Almost every command in the Fundamentals part of this book works on almost every Linux computer. But rename is different.

Try to use mv whenever you need to rename only a couple of files.

rename on Debian/Ubuntu

The rename command on Debian uses regular expressions (regular expression or shor regex are explained in a later chapter) to rename many files at once.

Below a rename example that switches all occurrences of txt to png for all file names ending in .txt.

paul@debian7:~/test42$ ls
abc.txt  file33.txt  file42.txt
paul@debian7:~/test42$ rename 's/\.txt/\.png/' *.txt
paul@debian7:~/test42$ ls
abc.png  file33.png  file42.png

This second example switches all (first) occurrences of file into document for all file names ending in .png.

paul@debian7:~/test42$ ls
abc.png  file33.png  file42.png
paul@debian7:~/test42$ rename 's/file/document/' *.png
paul@debian7:~/test42$ ls
abc.png  document33.png  document42.png
paul@debian7:~/test42$

rename on CentOS/RHEL/Fedora

On Red Hat Enterprise Linux, the syntax of rename is a bit different. The first example below renames all *.conf files replacing any occurrence of .conf with .backup.

[paul@centos7 ~]$ touch one.conf two.conf three.conf
[paul@centos7 ~]$ rename .conf .backup *.conf
[paul@centos7 ~]$ ls
one.backup  three.backup  two.backup
[paul@centos7 ~]$

The second example renames all (*) files replacing one with ONE.

[paul@centos7 ~]$ ls
one.backup  three.backup  two.backup
[paul@centos7 ~]$ rename one ONE *
[paul@centos7 ~]$ ls
ONE.backup  three.backup  two.backup
[paul@centos7 ~]$

practice: working with files

1. List the files in the /bin directory

2. Display the type of file of /bin/cat, /etc/passwd and /usr/bin/passwd.

3a. Download wolf.jpg and LinuxFun.pdf from http://linux-training.be (wget http://linux-training.be/files/studentfiles/wolf.jpg and wget http://linux-training.be/files/books/LinuxFun.pdf)

wget http://linux-training.be/files/studentfiles/wolf.jpg
wget http://linux-training.be/files/studentfiles/wolf.png
wget http://linux-training.be/files/books/LinuxFun.pdf

3b. Display the type of file of wolf.jpg and LinuxFun.pdf

3c. Rename wolf.jpg to wolf.pdf (use mv).

3d. Display the type of file of wolf.pdf and LinuxFun.pdf.

4. Create a directory ~/touched and enter it.

5. Create the files today.txt and yesterday.txt in touched.

6. Change the date on yesterday.txt to match yesterday's date.

7. Copy yesterday.txt to copy.yesterday.txt

8. Rename copy.yesterday.txt to kim

9. Create a directory called ~/testbackup and copy all files from ~/touched into it.

10. Use one command to remove the directory ~/testbackup and all files into it.

11. Create a directory ~/etcbackup and copy all *.conf files from /etc into it. Did you include all subdirectories of /etc ?

12. Use rename to rename all *.conf files to *.backup . (if you have more than one distro available, try it on all!)

solution: working with files