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Linux Command-Line Cheat Sheet

By Benjamin Mako Hill and Jono Bacon
August 14, 2007 12:00 PM ET
Searching and Editing Text Files

Search and edit text files by using the following commands.

  • grep: The grep command allows you to search inside a number of files for a particular search pattern and then print matching lines. For example, grep blah file will search for the text "blah" in the file and then print any matching lines.

  • sed: The sed (or Stream EDitor) command allows search and replace of a particular string in a file. For example, if you want to find the string "cat" and replace it with "dog" in a file named pets, type
    sed s/cat/dog/g pets.
Both grep and sed are extremely powerful programs. There are many excellent tutorials available on using them, but here are a few good Web sites to get you started:
Three other commands are useful for dealing with text.
  • cat: The cat command, short for concatenate, is useful for viewing and adding to text files. The simple command cat FILENAME displays the contents of the file. Using cat FILENAME file adds the contents of the first file to the second.

  • nano: Nano is a simple text editor for the command line. To open a file, use nano filename. Commands listed at the bottom of the screen are accessed via pressing Ctrl followed by the letter.

  • less: The less command is used for viewing text files as well as standard output. A common usage is to pipe another command through less to be able to see all the output, such as ls | less.

The Linux Command Line

Dealing with Users and Groups

You can use the following commands to administer users and groups.
  • adduser: The adduser command creates a new user. To create a new user, simply type sudo adduser $loginname. This creates the user's home directory and default group. It prompts for a user password and then further details about the user.

  • passwd: The passwd command changes the user's password. If run by a regular user, it will change his or her password. If run using sudo, it can change any user's password. For example, sudo passwd joe changes Joe's password.

  • who: The who command tells you who is currently logged into the machine.

  • addgroup: The addgroup command adds a new group. To create a new group, type sudo addgroup $groupname.

  • deluser: The deluser command removes a user from the system. To remove the user's files and home directory, you need to add the
    -remove-home option.

  • delgroup: The delgroup command removes a group from the system. You cannot remove a group that is the primary group of any users.

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