In my Mac OSX Command Line Essentials post I describe some basics of command line use. About 90% of what’s there is equally applicable in Linux. If the command line is entirely new to you I’d suggest starting there because I’ll be introducing a few more advanced topics here.

Contents

man to read the manual {#man}

The man command allows you to see a ‘manual’ for a given command but these are often quite unwieldy. Here are a few tips for finding what you need within a man page:

  • \ to search (either a simple string or regular expression will work)
  • h to get help

chmod to change permissions {#chmod}

chmod can be used to alter a file’s permissions. It can be a little confusion because it provides several forms of command syntax to achieve the same thing. These including octal, binary and to perhaps easiest to grasp to the mnemonic form. For users the mnemonic forms are: u for user, g for group, o for other, a for all. For permissions it’s: r for read, w for write and x for execute

For example:

  • chmod a-r foo.txt removes ‘read’ permissions from ‘all’
  • chmod u+rw foo.txt adds ‘read’ and ‘write’ permissions for ‘user’
  • chmod u+rw -R bar/ adds ‘read’ and ‘write’ permissions for the ‘bar’ directory and its contents recursively

tail {#tail}

The tail command prints the last 10 lines of a file. A lesser known but extremely useful variant is the -f option which allows you to keep the file open and print any new lines as they are appended. In addition, you can use the --retry option if the file doesn’t exist.

locate and find {#locate-and-find}

These two commands can be used to find files but they work in different ways. Simply put: locate is easier but find is more powerful.

locate searches a database of pathnames and returns every name that matches a given substring. For example:

  • locate .js --count tells me that there are currently 14,151 pathnames that contain the ‘.js’ substring listed in the database on my machine. Without --count they’d all be output
  • locate --regex ".s?css$" lists all the pathnames that end with either ‘.css’ or ‘.scss’

find is better because it searches a given directory and has many powerful options. Rather than describe them I’ll provide some examples:

  • find ~ lists everything in my home directory
  • find ~ -regex '.*\.min\.css$' lists all ‘.min.css’ files in my home directory
  • find ~ -type f lists every file (there is also a d option)
  • find ~ -type f -name "*.js" -size +1M | wc -l tells you how many ‘.js’ files are larger than one MB. You can see how something like this might be useful for testing.
  • find ~ -cmin -4 -type f will show all files with contents or attributes that were last modified less than 4 minutes ago (there is also a -mmin option which looks for content changes only).

This is really just the beginning to there is lots you can achieve with find.

Shutdown {#shutdown}

One of the things I initially missed when moving from Mac to Linux was the ability within Alfred to quickly shut down or restart a machine.

  • shutdown -h now to will shut down immediately
  • shutdown -r now to will restart immediately

There are other options that can be found on the man page.

Assorted cool stuff {#assorted}

  • sudo !! run the last command as root (Note: omitting sudo simply runs the last command
  • Ctrl + x, e temporarily open Vim to edit the command
  • Alt + . place the argument from the last command on the shell

I hope you’ve found these few tips helpful 🙂