Basic linux commands
Post on 09-Jul-2015
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BASIC LINUX COMMANDS
Welcome to the Linux World
What are linux commands
Linux commands are just simple programs like a program in windows. Typing command is like clicking an icon in windows.
Sometimes commands take some extra parameters to do extra work, we call them flags.
man (Your best friend!)
man means manual pages, its like reading a manual of any home appliance. In software it means reading documentation. Good softwares have always a good documentation part.
$ man <command>$ man clear
ls (list items)
● The ls command ( lowercase L and lowercase S ) lists the contents of your current working directory.
● ls by default does not show hidden files
● to see all files use ls -al● -al is flag in this case
mkdir (make directory)
● creates a directory● use -p to create as many directories.● $ mkdir first/second/third -p● $ cd first/second/third
cd (change directory)
● changes the current directory ● cd . to remain inside same directory● cd .. to go back one directory
pwd (print working directory)
For example, to find out the absolute pathname of your home-directory, type cd to get back to your home-directory and then type
$ pwdit will print current directory
~ Your Home Directory
By typing cd ~ in terminal it will take you to the home directory of current user$ cd ~
cp (copy)
copies a file or entire directory to another pathIf you want to copy files from another directory to current directory use a . for destination$ cp <source_file> <destination_file>Tip: Always read the error carefully and please don't freak out :)
mv (move file)
move command renames or move a file
use -r flag to recursively move all files
$ mv file1.txt file2.txt
rm (remove)
rm removes a file or entire directory with -r flag
$ rm <file>$ rm <directory> -r
clear
clears your screen
$ clear
cat
displays the content of files on screen.
$ cat file.txt
less
Iess is similar to cat but it displays content one page at a time
$ less file.txt
head
head is a short version of less command. It prints only first 10 lines.
You can set the number of lines by giving a -<number> flag e.x$ head -5 file.txt
tail
tail is opposite to head, it shows last 10 lines of the file.
searching within text
You can use less command to search within text. Do you remember what less command do?After executing the less command use / and type your required text to search$ less file.txt/science
grep (don't ask what that’s called :) )
This command search a file for specific word or a pattern. for examplegrep Science file.txt will search string Science in file.txt
grep command by default is case sensitive
wc (word count)
counts number of words in a given file.
to find number of lines set the -l flag
$ wc -l file.txt
Writing input to output
type the cat command without file name. It will start taking your text into output memory. Once you press Ctrl + d the output will be printed on screen.$ cat$ alpha $ Ctrl + d
use cat to write a file
$ cat > file.txtThis will take your input and write to a file by name file.txt from your input until Ctrl+d is pressed.
Pipes
Piping means passing result of one command to another command.
You can search in first 10 lines by using head and grep command by piping$ head file.txt | grep science
The wildcard *
The * character is a wildcard character. It means it will ignore the part after and before where its used$ ls list*will list all files starting with string list$ ls *listwill list all files ending with string list
UNIX File System
Type ls -l and see the result
UNIX File SystemIn the left-hand column is a 10 symbol string consisting of the symbols d, r, w, x, -, and,
occasionally, s or S. If d is present, it will be at the left hand end of the string, and indicates a
directory: otherwise - will be the starting symbol of the string.
The 9 remaining symbols indicate the permissions, or access rights, and are taken as three groups of
3.
● The left group of 3 gives the file permissions for the user that owns the file (or directory) (thirdknife in the above example);
● the middle group gives the permissions for the group of people to whom the file (or directory) belongs (staff in the above example);
● the rightmost group gives the permissions for all others.The symbols r, w, etc., have slightly different meanings depending on whether they refer to a simple
file or to a directory.
chmod (changing file mode)
Only owner can change the mode.Symbol Meaning
u user
g group
o other
a all
chmod (changing file mode)Symbol Meaning
r read
w write (and delete)
x execute (and access directory)
+ add permission
- remove permission
Example
$ chmod a+rw file.txtthis will give read and write access to all user, group and others
-rwxrwxrwx 1 thirdknife staff 5 Nov 27 23:09 text.txt
making file executable and runnable
For any file to be executable you have to make it x using chmod, e.g$ chmod a+x file.txt this will make file.txt executable for all (user, group and others)to execute a file use ./<filename>
sudo (execute commands as others)
Use this command to do as a different user.
$sudo su lswill list files as root user $sudo su - shakeel ls will list files as shakeel user
Tips
Always use manual pages for help.I understand they are boring but believe me thats where I learned the most. Second friend is google :)
Try to understand the error statement.
Contact
shakeel@creanyx.com
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