Chown command cheat sheet

1. Change the owner of a file

# chown [owner_name] [file_name]

Example

# chown root temp.txt

2. Change the group of a file

# chown :[group_name] [file_name]

Example

# chown :root temp.txt

3. Change both owner and the group

# chown [owner_name]:[group_name] [file_name]

Example

# chown root:root temp.txt

4. Using chown command on symbolic link file

# chown [owner_name]:[group_name] [file_symbolic_link]

Example

# chown root:root temp_symlnk

with -h flag change will be enforced

# chown -h root:root temp_symlnk

with -R flag we can use chown against symbolic link directory

# chown -R -H root:root temp_symlnk

5. Change owner only if a file is owned by a particular user

# chown --from=[owner_name] [new_owner_name] [file_name]

Example

# chown --from=root jenkins temp.txt

6. Change group only if a file already belongs to a certain group

# chown --from=:[group_name] :[new_group_name] [file_name]

Example

# chown --from=:root :jenkins temp.txt

7. Copy the owner/group settings from one file to another

# chown --reference=[source_file] [destination_file]

Example

# chown --reference=settings.txt temp.txt

8. Change the owner/group of the files by traveling the directories recursively

# chown -R [user_name]:[group_name] [directory_name]/

Example

# chown -R jenkins:jenkins jenkins/

9. List all the changes made by the chown command

# chown -v -R [user_name]:[group_name] [file_name]

Example

# chown -v -R root:jenkins temp.txt

Working with ZIP in terminal

Couple of days ago wanted to use ZIP in OSX terminal and realised that I don't have examples really (yes U can check manuals etc.) so I've decided just to note most common / usable ones:

- zip --encrypt file.zip files - will create an encrypted zip archive (files won't be removed automatically after compressing);

- zip -r archive.zip directoryName - will compress whole directory at once. U can add --encrypt flag here as well

- unzip file.zip - extracts file from archive into current directory

That's it for now although most likely will have to add more later on.

Math calculation with Bash in OSX

There are quite a few options how to calculate with Bash in OSX terminal but for reference I'd like to mention just several of them which can be used as a baseline.

echo "2 * 2" | bc

echo "scale=3; 1000/52 | bc" - will output result + 3 digits after comma

bc <<< "100 / 3"

bc -l <<< "sqrt(5)" (scale(3.3) - number of digits after comma, length(100) - number of digits)

awk "BEGIN {print 33 * 33}"

Change File Permissions in Terminal OSX

Knowledge about changing permissions for a specific file is pretty important and can even save Your information from being lost.

So let's see what we can check and how.

1. Execute next command in Your terminal window:

$ ls -la

You should see same information as on screen below.

What do those letters form first column stand for?
- d = directory
- r = read access
- w = write access
- x = execute access
- - = no permissions at all

Column 3 indicates owner of a file and column four shows us an user's group which might has or not permissions to read/write/execute file.

So if we'll check first column again from left to write we'll see that:

- first symbol / several symbols - user's permissions
- second symbol (after dash) / symbols - group permissions
- third symbol / symbols - all other users permissions

Let's analyse example.txt file:

- user has read and write permissions
- group has read and write permissions
- other users have only read permission

2. If You want to change ownership of the file just execute:

$ sudo chown NEW_USER:NEW_GROUP example.txt

this command will update owner and group for this file.

3. If You want just update permissions for specific file then You need to execute:

$ sudo chmod 000 example.txt

this command deny all actions with this file for all users.

4. Let's explore octets in general:

- 0 - No read, no write, no execute  - " - "
- 1 - No read, no write, execute       - " -x "
- 2 - No read, write, no execute       - " -w- "
- 3 - No read, write, execute            - " -wx "
- 4 - Read, no write, no execute      - " r- "
- 5 - Read, no write, execute           - " r-x "
- 6 - Read, write, no execute           - " rw- "
- 7 - Read, write, execute                - " rwx "

5. So according to this table if we'll execute next command:

$ sudo chmod 432 example.txt

- owner will be able only to read file;
- group will be able to write and execute;
- all others will be able only to write.

6. If You want to apply same permission to folder and all its content You have to add one more flag to Your command:

$ sudo chmod -R 777 Documents

This is pretty much core knowledge which You have to have in order to change permissions for folder / file in OSX terminal.

BASH cheat sheet

Traditionally I'll put here some well known BASH commands for keeping those in one place in case I'll forget them :)

echo $BASH - should be /bin/bash - make sure that U're using bash :)

nano (vim) ~/.bash_history - shows all history of commands in bash
reset - resets terminal after crashing (eg trying to output binary file with less command etc.)

ls - list of content in current directory
ls -a - list of content in current directory including hidden files
ls -l - list of files in long format
ls -a /bin - list of all files in bin directory
ls -a Documents/ - list of all files in Documents directory without entering into that
ls -t - list by modification date
ls -S - list by size
ls -R - recursively list files in subdirectories
ls -d - don't go into subdirectories just list them
ls | wc -l - show how many files in the current directory

man - help for comands (Manual pages)
man ls - shows help related to ls command

Navigation inside man:
space - scrolls page down
b - scrolls page up
/ <option> - performs search inside help; for next occurrence of searched term press / + enter
q - exits help

pwd - Path to working directory
cd - changing directory / if without arguments navigates to Home directory
cd / - navigates to Root directory

file <filename> - shows information about file without opening it
file * - shows information about all files in current directory
open <filename> - opens file with default (specified in system) application
open <filename> -a <application> - opens file with wanted application
open . - opens current directory in Finder
cat <filename> - print content of file into console
less <filename> - show content of file with possibility of navigation (like inside of man)

tail <filename> - show end of the file
tail <filename> -n 5 - show last five lines of file
tail <filename> -f - show latest (realtime) updates in the file, suitable for debugging
head <filename> - show beginning of the file

mkdir <name> - creates a directory
touch <filename> - create an empty file (updates modification and access dates in case file already exists)
touch {a,b,c,}.txt ==> touch a.txt b.txt c.txt
touch {a..c}{1..3}.txt ==> touch a1.txt a2.txt ... c2.txt c3.txt

cp <filename with relative path> . - copy file to current directory
cp <filename with relative path> <new file name> - copy file to current directory with different name
cp -R <source directory / file> <target directory> - copy source directory / directories / files into target directory
rm <filename> - removes a file
rm -r <directory> - removes a whole directory
rmdir <directory> - removes an empty directory
mv <filename> - move a file (also can be used during renaming)
mv <filename>.. <directory> - move file / files into specified directory
mv file.{txt,jpg} dir/ ==> mv file.txt file.jpg dir/
cp / mv / rm -i - security switch - will ask if you are sure to perform an action

ls > <filename> - write content of directory into file - will override file  if exists
ls >> <filename> - write content of directory into file - will append information at the end of the existing file, otherwise will create a new file

ls | less - get output from first command and send it to input of second command

cut -f 3 <filename> | grep 4 | wc -l - get 3 rd column from file (assuming it's csv) then get all rows which contains 4  and then count how many lines contains that number

CTRL-r - reverse search in bash history - search for the latest occurrence. If wee need previous one just press CTRL-r again and so on. To exit from search mode without execution command we can use arrow (left, right) key

sort -nk2 <filename> - sort file by using second column (in space-separated file) as a key
sort -r <filename> - sort in reversed order
sort <filename> | uniq -c - sort file then counts how many time each line appeared
wc <filename> - show number of lines, words and bytes of the file
wc -l <filename> - show opnly number of lines

grep <search term> <filename> - search for all occurences in the file
grep <search term> *<filename pattern> - search for all occurences in several files
grep -i <search term> <filename> - search for all occurences in the file ignoring case
grep -v <search term> <filename> - invert search

find /bin - search for all files in bin directory
find /bin -name test - search for all files in bin directory with name test

ps ax - show all running processes
ps aux - show all running processes with owner
top - show more detailed information about running processes
CTRL-z bg - put program into background
CTRL-z fg - put program into foreground

open -a <program name> - start a program from shell
kill -KILL <process id> - hard kill for process which not responding

As usually I'm not pretending for full list of BASH options - as it's really huge but those listed above are the most common for daily usage :)

Executing OSX terminal commands from Java

Couple days ago I've faced a situation when I needed to execute a pipeline of commands in OSX terminal from Java code and return result into program itself. You may say that there's a lot of information in the Internet (as a lot of us would say) but after spending some time it went out that those solutions are a bit incomplete for me :) So I'll add some information for those who might need that.

Problem:
- execute command in OSX terminal from Java program and return result from terminal back to the program;

Solution:

public static void main(String[] args) 
                             throws IOException, InterruptedException {
   try {
        Runtime runtime = Runtime.getRuntime();
        String[] cmd = {"/bin/bash", "-c", "Your command goes here"};

        Process process = runtime.exec(cmd);

        BufferedReader input = 
           new BufferedReader(new InputStreamReader(process.getInputStream()));

        String line;

        while ((line = input.readLine()) != null) {
                System.out.println(line);
        }

    } catch (Exception e) {
        System.out.println(e.toString());
        e.printStackTrace();
    }
}

And it's simply all. So You might want to create some kind of service class for that command creation and then simply pass it to runtime executor - it's up to You.

Before the end just one more important detail:

Problem:
- execute pipeline of commands (where we need to execute 2 or more) and only after that return a result back to the program

Solution:
- here I'll show an example of such pipeline:

"cd /Users/Projects/Test && git checkout master && git checkout -b master-test && git log"

So You can add as many of Your commands as You need just separate those with && and that will work.

That's probably all for that topic.