Ctrl + A = beginning of line Ctrl + E = end of line
~ is the variable for the home directory
echo ~
Tab completion: tab twice to display all of the available options.
Clean up the terminal by using either Ctrl + L or running the command clear.
Manual: man echo displays information about commands. You exit by typing q).
pwd print out the current working directory.
ls list files in the pwd. You can pass in a directory ls Documents to list files in a specific directory. Or even pass in a list of directories: ls Documents Downloads. Since we can pass in space-separated values, we need to escape compound names by doing: ls Some\ Directory or ls "Some Directory".
ls -ldisplays details.ls -adisplay all files, even hidden ones.ls -tsorted by time they were last modified.- Any combination of the commands above.
.. one level up
. current directory
open . opens the current directory in Finder
open README.md uses the default app for markdown files
open -a Atom README.md uses the chosen app to open the file with
open -R README.md reveals file in Finder
open https://google.com opens the website using the default browser
killall Finder closes and re-opens Finder.
touch README.md creates a file named README.md in the current directory.
mkdir assets create a folder called assets in the current directory.
cp README.md README.md.bak if the new filename already exists, it will get overwritten.
cp -r sourceFolder targetFolder
mv README.md targetFolder move the README.md file to the targetFolder directory
mv README.md targetFolder/NEW-README.md move the file and also rename it at the same time.
mv README.md NEW-README.md renames file without moving it.
mv file* targetFolder using wildcards: this command will move file1, fileBlah and second file to the target directory.
rm README.md remove the file
rmdir someFolder this only works for empty folders.
rm -r someFolder recursively removes the folder and all its content
A symlink is a new file that points to another one.
This is how you create one: ln -s README.md RAWR.md. If you rename the README file, the soft link gets broken.
This is what the symlink looks like when we list all the files of the directory with ls -la:
lrwxr-xr-x 1 fknussel staff 9B 29 Oct 16:00 RAWR.md@ -> README.md
cat README.md echoes all the content of whatever file you pass to it. After creating a symlink, cat RAWR.md equals cat README.md.
ln README.md HARD-RAWR.md creates a HARD LINK. That means it doesn't matter if we rename the original README.md file, the hard link doesn't get destroyed.
find . -type f means: search the current directory for all files (files of type file).
find . -name README' means: find all files in the current directory named "README'.
find . -name *.txt using wildcards.
find . -size +2048 find all files weighing more than 1Mb. This is number of 512 bytes blocks.
find . -mtime -1 find by last modification time. -1 means 1 day old.
find . -atime -1 find by last access time.
find . -ctime -1 find by creation time.
find . -iname *.txt -or -iname *.doc we can also use -and and -or to refine our search conditions.
grep "Hello world" README.md returns the line of the match
grep -i "Hello world" README.md case insensitive search.
grep -il "Hello world" * returns the name of the file, not the line.
grep -ilr "Hello world" * searches recursively through the current directory.
- rw- r-- r--
|-|---|---|---|
A B C D
A) - for a regular file, d for a directory
B) User permissions (u): first space corresponds to r=read, second space corresponds to w=write, third space corresponds to x=execute.
C) Group permissions (g): r-- means that everyone else in the group can just read the file but neither can write on it or execute it.
D) Anyone else/others (o)
a stands for all.
chmod g+w README.md add write permissions to Group's users
chmod a+x README.md the plus (+) sign adds permissions
chmod a-x README.md the minus (-) sign removes permissions
chmod og-x README.md
chmod g+x-w README.md
chmod g=rwx README.md
chmod u=rw,g=,o=x README.md
chmod g= README.md means no permissions
Octal permissions:
chmod 444 README.md
the first 4 is u
the second 4 is g
the third 4 is o
- 4 stands for READ
- 2 stands for WRITE
- 1 stands for EXECUTE
- 0 takes away any permissions
For example: 7 = 4 + 2 + 1 = READ + WRITE + EXECUTE
echo "Hello world" > README.md
cat README.md // echoes "Hello world"
echo "new line" >> README.md
cat README.md // echoes "Hello world\nnew line"
echo "Start fresh" > README.md // overwrites the original file
Piping: sending the standard output of one program to the standard input of another.
cat README.md | grep "No such"
Returns all the lines in the README file having "No such" in them.
Another piping example: returns hidden files only. Since . is an special character, we need to escape it.
ls -a | grep "\."
top: takes continuous samples of processes running on your Mac. Type lowercase q to exit.
top -o cpu: orders them all by cpu usage (DESC).
ps -cx: process status. Doesn't take continuous samples, rather a snapshot.
ps -cvx: returns more info.
ps -cvx | grep "Google" looks for processes that match "Google" (Google Chrome, Google Chrome Helper, etc.)
Signals just force a process to stop and respond to the signal. There are two useful signals:
ten: short for terminate, a process will finish when it gets this signal.kill: force quit, this signal cannot be ignored. If an app crashes and it won't respond to "Force quit" from the UI, we can use thekillsignal from the command line. The way it works is:kill pid, wherepidis the process id we are trying to kill.
@TODO: killall?
- FTP, HTTP
- Grabs the content of a remote file. We can also use it to scrape web pages or download files or hit an API/Web Service.
curl https://google.com > google-index.html
curl -O http://10.0.1.201/simple.html # creates a local copy of simple.html
curl -of http://10.0.1.201/fake.html # grabs the content only if the remote file exists. If we don't use this option, we'd get a standard 404 page as a result.
#! /bin/bash
Where /bin/bash is the path to the interpreter.
This means: "Hey, use Bash to execute this code". This basically makes it equivalent to typing it all in the terminal.
Moving the .sh file to /usr/local/bin makes it always accessible so that I don't need to remember where the file is. Also make sure to chmod +x it to make it executable:
chmod +x something.sh
sudo cp something.sh /usr/local/bin
echo $PATH
Sometimes while working with long commands, you need to move the cursor to the start or end of the command. The traditional method of using arrow keys seems very slow in these cases. The faster alternative is to press Ctrl+A to send the cursor to beginning of the command, or Ctrl+E to send the cursor to the end of the command. Also, use the combination of Ctrl+right arrow key to move forward one word at a time, and Ctrl+left arrow key to move backwards one word at a time.
Writing names for existing files or directories while on the command line can be made faster by using the Tab key extensively. Just type in the starting few characters from the name of the file and then hit Tab. If these characters match only a single existing file or folder, the name will get autocompleted for you; otherwise options are displayed, in which case you can complete the name by typing a few more characters (to make the these initial characters unique) and hitting Tab again.
Everybody knows that the clear command can be used to clear the terminal screen, but for this you have to type and run this command from the prompt. If you do not want to run the clear command, Ctrl+L can be used to clear the screen while retaining whatever was there on the current prompt.
Using the mouse on command line for cut-copy-paste operations is not always advised. A quick text cut on the command line can be achieved by using Ctrl+K (make sure to place cursor at the beginning of the text to cut), while paste can be done using Ctrl+Y.
Bash remembers a history of the commands you type into it. You can use the up and down arrow keys to scroll through commands you've recently used. The history command prints a list of these commands, so you can pipe it to grep to search for commands you've used recently.
3785 ls
3786 clear
3787 vagrant up
You can even use this associated id to execute these commands again:
!3787
Sometimes you may want to re-run a complex/long command that you executed a while ago. Usually we use the up and down arrow keys to search previously run commands. To speed things up, reverse search can be used. Just press Ctrl+R and write few characters from the start of command you're looking for. If you still don't get the required result, try pressing Ctrl+R repeatedly to loop through the results.
Yes. You can refer to last command you run with !! and use sudo before it.
There are certain files in Linux which store system-wide and user-specific configuration information. Usually these type of files start with a dot and are kept hidden. This means that these files are not visible if you do a simple ls in the directory where they reside. Run ls -a instead.
The ls command has a number of params:
-llong format, displaying Unix file types, permissions, number of hard links, owner, group, size, last-modified date and filename-fdo not sort. Useful for directories containing large numbers of files.-Fappends a character revealing the nature of a file, for example, * for an executable, or / for a directory. Regular files have no suffix.-alists all files in the given directory, including those whose names start with "." (which are hidden files in Unix). By default, these files are excluded from the list.-Rrecursively lists subdirectories. The command ls -R / would therefore list all files.
Use the mv command with the filename first and the destination directory as the second argument:
mv README.md ../
Use the same mv command for this:
mv my_filename.{old,new}
rm <filename>
Main options are:
-r,-R,--recursiveremove directories and their contents recursively.-f,--forceignore nonexistant files, and never prompt before removing.-iprompt before every removal.
By default, rm does not remove directories; rmdir does. However, if the -r (recursive) option is specified, rm will remove any matching directories and their contents.
Delete all files but those with a particular name / extension:
rm !(*.c|*.py)
touch <filename>
You can also create multiple files all at once:
touch new_file{1,2,3}
mkdir <dirname>
The ~ character – also known as tilde – represents the current user's home directory. So, instead of typing cd /home/name to go to your home directory, you can type cd ~ instead. This also works with relative paths – cd ~/Desktop would switch to the current user's desktop.
Side note: cd takes you straight to the user's home (that is, cd equals cd ~).
. represents the current directory and the .. represents the directory above the current directory. So, cd .. goes up one level. These also work with relative paths – if you're in your Desktop folder and want to go to the Documents folder, which is in the same directory as the Desktop folder, you can use the cd ../Documents command.
pwd echoes out the current working directory. In fact, it stands for "print working directory".
Pipes allow you to send the output of a command to another command (streams). In the UNIX philosophy, each program is a small utility that does one thing well. For example, the ls command lists the files in the current directory and the grep command searches its input for a specified term. Combine these with pipes (the | character) and you can search for a file in the current directory.
ls | grep README
The * character is a wildcard that can match anything. For example, if we want to delete both really long file name and really very long file name from the current directory, we could run the following command:
rm really*name
If you run rm * instead, you'll delete every file in the current directory, so be careful.
The > character redirects a command's output to a file instead of another command (what the pipe does). For example, the following line runs the ls command to list the files in the current directory and, instead of printing that list to the terminal, it prints the list to a file named "file1" in the current directory:
ls > file1
This is useful for emptying files, too:
> ./logfile
Both > and >> are used to redirect output to a file. The difference is that > overwrites the existing content with new content while >> appends to existing content.
grep is a command-line utility for searching plain-text data sets for lines matching a regular expression. For instance, you can filter the output of the ifconfig command to find your private IP address easily using grep:
ifconfig | grep 192.168.
The cat program is a standard Unix utility that will output the contents of a specific file and can be used to concatenate and list files. The name is an abbreviation of catenate, a synonym of concatenate.
You can use cat to display the contents of a file:
cat /etc/passwd
... or of multiple files:
cat /etc/passwd /etc/hosts
You can also concatenate multiple files and store the result into a new file:
cat test test1 test2 > test3
You can use the head and tail commands for this.
tail -5 output
Here tail displays the last five lines from the file "output".
Similarly, there is a head command to display content from the beginning of a file.
head -10 output
Sometimes I experience problems reading long files using cat, as the text scrolls past the screen before I can read it. To prevent this from happening you can use the less command. All you need to do is run the ‘cat' command in the following way:
cat <filename> | less
This will hold the output until you continuously press the Enter key on your keyboard. To exit from this mode, just press Q.
It is a built-in command that places a string on the computer terminal. Basically, echo repeats on the display screen whatever follows it on the command line.
echo !! > script.sh
which shows the full path of (shell) commands.
which node
returns /usr/local/bin/node.
PATH is an environmental variable in Linux and other Unix-like operating systems that tells the shell which directories to search for executable files in response to commands issued by a user.
A list of all the current environmental variables and their values for the current user, including all the directories in the PATH variable, can be seen by running the env command without any options or arguments:
env
As there can be considerable output, it can be convenient to modify this command so that it displays just the PATH environmental variable and its value. This can be accomplished by using a pipe to transfer the output of env to the grep filter and use PATH as an argument to grep:
env | grep PATH
Another way to view the contents of just PATH alone is by using the echo command with $PATH as an argument:
echo $PATH
The dollar sign tells echo to output the value of the variable PATH rather than its name.
By default, Bash executes every command you run in the current terminal. That's normally fine, but what if you want to launch an application and continue using the terminal? If you type firefox to launch Firefox, it will take over your terminal and display error messages and other output until you close it. Add the & operator to the end of the command to have Bash execute the program in the background:
firefox &
You can also have Bash run two commands, one after another. The second command will only execute if the first command completed successfully. To do this, put both commands on the same line, separated by a && (double ampersand).
For example, the sleep command takes a value in seconds, counts down, and completes successfully. It's useless alone, but you can use it to run another command after a delay. The following command will wait five seconds, then launch the gnome-screenshot tool:
sleep 5 && gnome-screenshot
Working on Linux command line means switching between lot of directories. Say you are in a directory named A, then you move to another directory, say B. Now you want to come back to A again. Typing the complete directory path for A can be cumbersome at times. You can use the cd - shortcut instead.
- Find all the files whose name is README.md in the current working directory:
find . -name README.md
- Find all the README.md files in the /home directory ignoring capitalization:
find /home -iname README.md
- Find all directories system-wide whose name is workspace:
find / -type d -name workspace
- Find all of the php files:
find . -type f -name "*.php"
- Find all files system-wide that are 50 MB:
find / -size 50M
- Find all the files system-wide that are greater than 50 MB but less than 100 MB:
find / -size +50M -size -100M
- Find every .mp3 file system-wide that is more than 10 MB and delete them using a single command:
find / -type f -name *.mp3 -size +10M -exec rm {} \;
Search inside all of the .c files within the current directory and output only those that are making use of printf:
$ grep -l "printf" *.cIf we want to view the lines where the string is used, then we need to do:
$ find ./ -name "*.c" | xargs grep "printf"
ps aux | grep -v `whoami`
In order to kill a process, use the ps command to get the process id (PID) of the process you want to terminate and then issue a kill command for that PID.
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