Linux cheat sheet
ssh command consists of 3 different parts:
- ssh command instructs the system to establish an encrypted secure connection with the host machine.
- user_name represents the account that is being accessed on the host.
- host refers to the machine which can be a computer or a router that is being accessed. It can be an IP address (e.g. 192.168.1.24) or domain name(e.g. www.domainname.com).
ssh user_name@host(IP/Domain_name)ssh-keygencat [OPTION] [FILE]...- display contents of file
- view contents of multiple files
cat file1 file2- create file
cat >filename - to limit preview of content
cat file | morecat file | less - display line number in file
cat -n filename - display $ (end of line) in file
cat -e filename - display tab separated lines in file
cat -T filename - display multiple files
cat filename0; cat filename1; cat filename2- standard output with redirection
Standard output of a file can be added into a new file or existing file with ‘>‘ (greater than) symbol. Careful, existing contents of test1 will be overwritten by contents of test file.
cat test0 > test1similarly contents of multiple can be added into single file (new or existing)
cat test0 test1 test2 > testN - Appending standard output with redirection
The contents of test file will be appended at the end of test1 file.
cat test0 >> test1- Sorting Contents of Multiple Files in a Single File
This will create a file test4 and output of cat command is piped to sort and result will be redirected in a newly created file.
cat test0 test1 test2 test3 | sort > test4- to make a copy of file1 in the current working directory and call it file2
cp file 1 file2- to move or rename file1 to file2
mv file 1 file2- to remove file use the following
rm [OPTION]... FILE...- to remove empty directories from the filesystem
rmdir [-p] [-v | –verbose] [–ignore-fail-on-non-empty] directories …..- -
if filename is - (dash), you simply need to give can some indication that you want a litteral file of that name, not the internal alias it has. You can do this easiest by specifying a path to the file
cat ./-- # Pound/hash
Line beginning with # will not be executed. Used as a comment.
- ; Semicolon
Command separator [semicolon]. Permits putting two or more commands on the same line.
- . Dot
When working with filenames, a leading dot is the prefix of a "hidden" file, a file that an ls will not normally show.
When considering directory names, a . (single dot) represents the current working directory, and .. (two dots) denote the parent directory.
When matching characters, as part of a regular expression, a "." matches a single character.
- \ Backslash
A quoting mechanism for single characters.
- Space (in a filename)
cat "file name with space"or
cat file\ name\ with\ space- pwd
print path of the working directory
- ls
It is used to list information about files and directories within the file system.
ls [OPTIONS] [FILES]| option | description |
|---|---|
| ls -a | list all files including hidden file starting with '.' |
| ls --color | colored list [=always/never/auto] |
| ls -d | list directories - with ' */' |
| ls -F | add one char of */=>@ |
| ls -i | list file's inode index number |
| ls -l | list with long format - show permissions |
| ls -la | list long format including hidden files |
| ls -lh | list long format with readable file size |
| ls -ls | list with long format with file size |
| ls -r | list in reverse order |
| ls -R | list recursively directory tree |
| ls -s | list file size |
| ls -t | sort by time & date |
| ls -X | sort by extension name |
List root directory:
ls /List parent directory:
ls ..List user's home directory (e.g: /home/user):
ls ~List all subdirectories:
ls *- find
find [where to start searching from]
[expression determines what to find] [-options] [what to find]- grep
grep [options] pattern [files]| option | description |
|---|---|
| -c | This prints only a count of the lines that match a pattern |
| -h | Display the matched lines, but do not display the filenames. |
| -i | Ignores, case for matching |
| -l | Displays list of a filenames only. |
| -n | Display the matched lines and their line numbers. |
| -v | This prints out all the lines that do not matches the pattern |
| -e exp | Specifies expression with this option. Can use multiple times. |
| -f file | Takes patterns from file, one per line |
| -E | Treats pattern as an extended regular expression (ERE) |
| -w | Match whole word |
| -o | Print only the matched parts of a matching line, with each such part on a separate output line. |
- chmod
changes the permissions of the file.
chmod [options] mode[,mode] file1 [file2 ...]| option | description |
|---|---|
| u | user |
| g | group |
| o | other |
| a | all |
| r | read |
| w | write (and delete) |
| x | executable |
| + | add permission |
| - | take away permission |
- ps
will show the processes status as snapshot, information about your processes, with their associated PID and status, type
PID: Process ID, shows the process identification number.
TTY: Identifies the terminal from which the process was executed.
TIME: Shows the processor’s time occupied by the program.
CMD: Shows the command used to launch the process.
The & at the end runs the job in the background and returns the prompt straight away, allowing you do run other programs while waiting for that one to finish.
- jobs
list current jobs