Linux – basic commandsPosted in Linux By Maz On April 25, 2014
Linux is the most used Operating System for servers and the feature that is most fascinating is Command Line. Command Line is a program that is used to run commands and system interpret these commands.
Here are some beginner commands that a new Linux user can use in his learning. In Linux file name and commands are case sensitive.
There are “\” and “/” those are important to understand. “\” is used to escape characters while “/” is directory separator.
“.” is used to represent current directory. if used in start of a file name it hides that file.
“..” – parent directory.
“~” – User’s home directory.
“*” is used to represent one or more characters in a file name. file*.txt can be file2003.txt or file6.txt
“?” represent a single character in a file name. hello?.php can be helloz.php or hello1.php
“[ ]” represent a range of values.
“|” represent pipe. It redirects output of one command to other command – ls | more
“>” redirects output of a command to a new file. If file already exists then it overwrites the file.
like ls | output.txt
“>>” redirects output of a command to the end of an existing file. like
echo "hello" > file.txt
“<" redirect a file as input to a program. ";" command separator. this operator separates multiple commands on a single line, can be executed on a single line. "&&" is a command separator but it executes second command if first command finished without errors. "&" executes a command in back end. Linux File system. Linux has a tree-structure like folders and files hierarchy. "/" is the root or base level directory. All other directories are child directories of this directory.
“/bin” – binary programs are stored in this directory.
“/boot” – boot loader files
“/etc” – host related files
“/dev” – device or hardware related files
“/lib” – kernel modules, shared libraries
“/home” – user’s personal home files and directories.
“/proc” – process related information
“/root” – root is the admin or super user in a Linux operating system, this directory is home directory of root user.
“/tmp” – temporary files
“/sbin” – system binaries
“/usr” – shareable data
“/usr/bin” – user’s programs are kept here
“/usr/include” – header files of c complied files
“/usr/local” – locally installed files are stored in this directory
“/usr/sbin” – none-vital system files
“/usr/share” – independent data of Linux architecture
“/usr/src” – Linux kernel and source programs
“/var” – variable data such as logs
ls – command is used to list directory contents.
ls -a or ls --all – this command is used to display all hidden contents of a directory or files starting with .
Help for a command.
We can see help for a particular command by typing -h or –help command.
ls -h or grep --help
Manual pages are used to find more help about a command.
Example: ls man
cd – Change directory – This command is used to change current directory.
pwd – print working directory
file – tells about type of file
file /bin/ls will output file type as execute able.
cat – displays contents of a file.
head – displays few top lines of a file
tail – displays few last lines of a file
cp – copies a file from one location to other
cp file1.html /var/www/html/file1.html
mv – moves a file from one location to other location
mv file1.html /var/www/html/file1.html
rm – removes a files
mkdir – makes a new directory
rmdir – removes a directory
which – displays location of a command.
locate – search a file like
ps – list all currently running processes
w – list all logged users and what activity they are doing
id – prints user id and group id
du – displays disk usage
df – displays disk file system usage
top – displays all the processes running in system in real time
free – displays amount of free and used memory in the system.
cat /proc/cpuinfo – displays information about the CPU.
cat /proc/meminfo – display lots of information about current memory usage
uname -a – prints system information to the screen
clear – clears the screen
more – display a file, or program output one page at a time
less – display a file, or program output one page at a time, can be scrolled backwards
grep – Search for a pattern in a file or program output.
lpr – print a file or program output. E
sort – sort a file or program output.
su – allows to switch other user’s account such as switch to root user account.
history – shows history of a command
Tab is used to autocomplete a command.
This was an introduction to Linux and basic commands in next chapters we will explore more advanced topics
Maz is a software engineer, and a Zend Certified Engineer . His area of expertise contains PHP /Mysql, Node JS / MongoDB, Angular JS, IOS and android.