input----> Command ----> Output
input redirection <
output redirection >
cat f1 > f2
to display file contents
cat without any arguments ….takes from the terminal and writes to the terminal so reads from keyboard and displays on screen this will be infinite loop .
cat f1 >> f2 [APPEND]
read from standard input and show page by page on standard output.
- is a easy way to create a file which does not exist
- if it exists its access time is updated unlike cat it does not display
ls- lists the files/directories in a directory
- color has a meaning which can be found out using –color option.
- files starting with [.]DOT are hidden files.
/[Slash]- Root directory
dev: all devices
lib: library's for every one.
lost+found: specific to redhat recovered files
proc: mapping to memory.
tmp : temporary files
var : variety of log files
bin: binaries of commands like ls mkdir etc.
boot: boot loader files, kernel etc
sbin: system binaries
mnt: any mountable devices like cdrom pendrive are mounted under this.
./ : current working directory
.. : parent directory
~ : Home directory (available only in few shells)
PWD : print working directory
CD: change directory, cd without any arguments takes to the home directory
to go to home u can use cd $HOME , cd ~ or just cd.
mkdir: <dir name …..>make a directory, on success does not give any message ,, instead u can use –V for verbose.
mkdir –p make parents as necessary.
rmdir <dir name ….> removes the specific dir
ls *: all the files
ls f?: list files which start with f and have one more leter.
ls f/ls f[1-4]: f followed by one of 1-4
Note for copy and move
- Use option -i to make it interactive along with v so that you have a say whether you have to overwrite or not .
- use -r to move or copy recursively.
- use –v to make it verbose.
- -f to make it silent.
- -b to take a back up before overwrite as we have bvf option is safest.
cp <source file> <dest file>
cp <source files…….> <dest file>
mv <source file> <dest file>
mv <source files…….> <dest file>
rm: removes files completely very hard to recover.
rm –rf ~ [ most dangerous command ]