Handy commands in Mac/Linux systems

Here’s a list of common commands I use in Linux. I will continue to update this list with more stuff.

  1. Checking fireball logs:
  2. [code lang=”bash” gutter=”false”]
    cat /var/log/appfirewall.log

    # You will see stuff like
    Jun 21 10:37:51 prakhars-MacBook-Pro Firewall[90]: postgres is listening from proto=6
    Jun 21 10:38:11 prakhars-MacBook-Pro Firewall[90]: mysqld is listening from ::ffff: proto=6
    Jun 21 10:40:21 prakhars-MacBook-Pro Firewall[90]: Dropbox is listening from proto=6
    Jun 21 10:40:21 prakhars-MacBook-Pro Firewall[90]: java is listening from ::ffff: proto=6
    Jun 21 10:44:38 prakhars-MacBook-Pro Firewall[90]: GoogleTalkPlugin is listening from proto=6
    Jun 21 10:45:35 prakhars-MacBook-Pro Firewall[90]: python is listening from proto=6

  3. screen command: Use it to create parallel sessions in terminal. Useful for running long processes on remote servers even after signing out of server.Usage:
    [code lang=”bash”]
    # This creates a separate screen.

    screen -ls
    #lists all attached/detached screens IDs

    screen -x 13152
    # Enter (Attach) screen ID 13152 (just an example, can be any ID number)

    echo $STY
    # Displays current screen ID you are working in.
    Ctrl-a d Detach from current screen.

  4. dpkg --get-selections List all installed packages. (Only on debian systems like Ubuntu which support apt-get)
    Smartly grep to find package you are looking for eg- dpkg --get-selections | grep mysql

Using Django using VirtualEnv on MAC. Fast forward installation.

This is a fast forward tutorial which will guide you through django installation on virtualenv. Detailed installation instructions using source codes can be found on respective package’s official site.

Pre- Requirements:
Make sure you have easy_install on MAC
Install pip using easy_install pip

1) Installing Virtualenv: Run following lines in terminal:

[code lang=”bash” gutter=”false”]
pip install virtualenv
pip install virtualenvwrapper

# Use a text editor to edit .profile and Insert following lines. Eg using vim:
# $ vim .profile
export WORKON_HOME=$HOME/.virtualenvs
source /usr/local/bin/virtualenvwrapper.sh

# Now open a new terminal window and Type:
mkvirtualenv myfirstproject

# You will see something like:
(myfirstproject) $

# This means you are now working isolatedly in myfirstproject
# The location of this project is ~/.virtualenvs/myfirstproject

2) Installing Django and South:

[code lang=”bash” gutter=”false”]

# [info] Make sure you are inside myfirstproject:
# $ workon myfirstproject
# Now run in terminal:

pip install Django
pip install south

# This installs Django in: .virtualenvs/myfirstproject/lib/python2.6/site-packages/django/


3) Starting first django project:

  • [info] Type workon myfirstproject if you are not already in your virtual environment.
  • [info] you can directly go to your site packages dir by typing cdsitepackages
  • [info] can check the location of django-admin by which django-admin.py
  • Initiating django project now. Assuming you are at .virtualenvs/myfirstproject/ Type:
  • django-admin.py startproject mydjangoproject
  • This will start your first django project.
  • Now start server by
  • python manage.py runserver Default port is 8000. If you have to change port, just write port number after runserver
  • Now, Visit browser at localhost:8000
  • Congrats, we have just installed a basic django app.

Display file permissions as octal number in ls command

Normally, in *nix systems like Linux, mac the file permissions are displayed as symbolic notations. So when doing a ls -l in a directory you’ll see drwxr-xr-x+ like symbolic permissions next to a directory. This is equivalent to 755 in octal permissions. I find octal permissions easier to grasp and understand. Unfortunately, there is no native switch in ls to show octal permissions. So here is a little custom command that will do the needful.

[code lang=”bash”]
ls -l | awk ‘{k=0;for(i=0;i<=8;i++)k+=((substr($1,i+2,1)~/[rwx]/)*2^(8-i));if(k)printf("%0o ",k);print}’

This command will show octal file permissions before its symbolic representation.

If you find it impressive and would like to bookmark it, just add this line in your ~/.profile or ~/.bash_profile (depending on mac or linux) using your favorite editor (I’d use vim).

[code lang=”bash”]
alias l= "ls -la | awk ‘{k=0;for(i=0;i<=8;i++)k+=((substr(\$1,i+2,1)~/[rwx]/)*2^(8-i));if(k)printf(\" %0o \",k);print}’"

We have just escaped $ and " with a \ in above line.

Some under-the-hood details: This command works by piping the output of ls -l to awk as its input. awk is a pattern directed scanning and processing language. For more info you can do man awk which shows:

Awk scans each input file for lines that match any of a set of patterns specified literally in prog or in one or more files specified as -f progfile. With
each pattern there can be an associated action that will be performed when a line of a file matches the pattern. Each line is matched against the pattern
portion of every pattern-action statement; the associated action is performed for each matched pattern. The file name – means the standard input. Any file
of the form var=value is treated as an assignment, not a filename, and is executed at the time it would have been opened if it were a filename. The option
-v followed by var=value is an assignment to be done before prog is executed; any number of -v options may be present. The -F fs option defines the input
field separator to be the regular expression fs.

An input line is normally made up of fields separated by white space, or by regular expression FS. The fields are denoted $1, $2, …, while $0 refers to
the entire line. If FS is null, the input line is split into one field per character.

A pattern-action statement has the form

pattern { action }

A missing { action } means print the line; a missing pattern always matches. Pattern-action statements are separated by newlines or semicolons.

MAC View file transfer speeds while copying

Often while copying large files from external hard disks, you want to see the transfer rates. MAC natively doesn’t show the transfer speed. However there’s a workaround:

1) open Terminal and write:

[code lang=”bash” light=”true”]
while true ; do iostat -w 2 ; done

This will show real-time data transfer speed of all mounted disks. Like:
[code lang=”bash” light=”true”]
$ while true ; do iostat -w 2 ; done
disk0 disk1 cpu load average
KB/t tps MB/s KB/t tps MB/s us sy id 1m 5m 15m
71.23 134 9.35 44.69 45 1.96 21 22 58 1.61 1.94 1.90
70.61 237 16.33 66.18 169 10.95 8 30 63 1.48 1.91 1.88
77.30 109 8.22 16.09 605 9.50 8 33 59 1.48 1.91 1.88
385.81 20 7.53 21.54 449 9.44 8 28 64 1.44 1.89 1.88
243.28 17 4.04 14.09 319 4.39 7 26 67 1.44 1.89 1.88