working with files

All files are case sensitive

Linux is 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

root@linux:~/Linux$ ls

winter.txt Winter.txt

root@linux:~/Linux$ cat winter.txt

It is cold.

root@linux:~/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. Even a

terminal window (/dev/pts/4) or a hard disk (/dev/sdb) is 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. Your editor does not care whether a file ends in .TXT or .DOC. As a

system administrator, you should use the file command to determine the file type.

Here are some examples on a typical Linux system.

root@linux:~$ file pic33.png

pic33.png: PNG image data, 3840 x 1200, 8-bit/color RGBA, non-interlaced

root@linux:~$ file /etc/passwd

/etc/passwd: ASCII text

root@linux:~$ 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

One easy way to create a file is with touch.

root@linux:~/test$ touch file1

root@linux:~/test$ touch file2

root@linux:~/test$ touch file555

root@linux:~/test$ ls -l

total 0

-rw-r--r-- 1 paul paul 0 2007-01-10 21:40 file1

-rw-r--r-- 1 paul paul 0 2007-01-10 21:40 file2

-rw-r--r-- 1 paul paul 0 2007-01-10 21:40 file555

#touch –t

Of course, touch can do more than just create files. Can you determine what by

looking at the next screenshot? If not, check the manual for touch.

root@linux:~/test$ touch -t 200505050000 SinkoDeMayo

root@linux:~/test$ touch -t 130207111630 BigBattle

root@linux:~/test$ ls -l

total 0

-rw-r--r-- 1 paul paul 0 1302-07-11 16:30 BigBattle

-rw-r--r-- 1 paul paul 0 2005-05-05 00:00 SinkoDeMayo

#rm

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!

root@linux:~/test$ ls

BigBattle SinkoDeMayo

root@linux:~/test$ rm BigBattle

root@linux:~/test$ ls

SinkoDeMay

#rm –i

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

root@linux:~/Linux$ touch brel.txt

root@linux:~/Linux$ rm -i brel.txt

rm: remove regular empty file `brel.txt'? y

root@linux:~/Linux$

#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.

root@linux:~$ ls test

SinkoDeMayo

root@linux:~$ rm test

rm: cannot remove `test': Is a directory

root@linux:~$ rm -rf test

root@linux:~$ ls test

ls: test: No such file or directory

#cp

To copy a file, use cp with a source and a target argument. If the target is a directory,

then the source files are copied to that target directory.

root@linux:~/test$ touch FileA

root@linux:~/test$ ls

FileA

root@linux:~/test$ cp FileA FileB

root@linux:~/test$ ls

FileA FileB

root@linux:~/test$ mkdir MyDir

root@linux:~/test$ ls

FileA FileB MyDir

root@linux:~/test$ cp FileA MyDir/

root@linux:~/test$ ls MyDir/

FileA

#cp –r   

To copy complete directories, use cp -r (the -r option forces recursive copying of

all files in all subdirectories).

root@linux:~/test$ ls

FileA FileB MyDir

root@linux:~/test$ ls MyDir/

FileA

root@linux:~/test$ cp -r MyDir MyDirB

root@linux:~/test$ ls

FileA FileB MyDir MyDirB

root@linux:~/test$ ls MyDirB

FileA

cp 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.

cp file1 file2 dir1/file3 dir1/file55 dir2

#cp –I    

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

root@linux:~/test$ cp fire water

root@linux:~/test$ cp -i fire water

cp: overwrite `water'? no

root@linux:~/test$

#cp –p  

To preserve permissions and time stamps from source files, use cp -p.

root@linux:~/perms$ cp file* cp

root@linux:~/perms$ cp -p file* cpp

root@linux:~/perms$ ll *

-rwx------ 1 paul paul 0 2008-08-25 13:26 file33

-rwxr-x--- 1 paul paul 0 2008-08-25 13:26 file42

cp:

total 0

-rwx------ 1 paul paul 0 2008-08-25 13:34 file33

-rwxr-x--- 1 paul paul 0 2008-08-25 13:34 file42

cpp:

total 0

-rwx------ 1 paul paul 0 2008-08-25 13:26 file33

-rwxr-x--- 1 paul paul 0 2008-08-25 13:26 file42

#mv

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

root@linux:~/test$ touch file100

root@linux:~/test$ ls

file100

root@linux:~/test$ mv file100 ABC.txt

root@linux:~/test$ ls

ABC.txt

root@linux:~/test$

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