| Command | Description
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| ls | List contents of a directory, use -l to get more information.
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| cd | Change Directory; with no arguments, goes to your home directory.
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| rm | Remove (delete) a file. Use -r to remove a directory, but be careful!
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| cp | Copy a file. If you give more than two arguments and the last is a directory, it will copy all the files into the directory. Use -R to copy directory trees.
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| rmdir | Remove a Directory, but only if it's empty (otherwise use rm -r).
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| mkdir | Make a Directory (create a new one).
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| touch | Change the modification times of a file, or create one by that name if one doesn't exist. Useful before make, which checks timestamps to decide which commands to run.
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| du | Disk Usage - tells you how much space files take up.
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| pwd | Print Working Directory - tells you your current directory.
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| umask | Sets the mask for creating new files - new file permissions will be 777 - the value you give to umask (except new files don't get execute permissions).
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| ln | Link - creates a link from one file to another (use -s for symbolic links, which you usually want to do).
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| chmod | Change mode - set file permissions. Chmod <number> <filename> sets the file's permissions to the number, whose digits are combinations of 4 (read), 2 (write), and 1 (execute), and the hundreds digit tells owner permissions, the tens digit group permissions, and the ones digit world permissions.
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| chown | Change owner - give a file to another user.
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| chgrp | Change group - give a file to another group.
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| whoami | Tells you your username (the special syntax "who am i" also works).
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| who | Tells who's logged onto the system.
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| finger | With no arguments, tells who's logged onto the system; when given a username, gives more info about that user.
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| w | Tells who's logged onto the system, and what command they've last run.
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| su | Super User - Assume permissions of another user (usually root).
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| sudo | Super User Do - Used as a prefix for a command; it gives you root privileges for the purposes of that command.
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| passwd | Password - Change your password.
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| vi | The best editor ever (take that, Sam!).
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| cat | Concatenate - prints out the contents of file(s).
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| tac | Prints out files backwards (the name is cat backwards).
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| head | Prints the beginning lines of a file.
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| tail | Prints out ending lines of a file.
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| less | Shows a file a page at a time.
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| od | Octal dump - print out a file, with octal character numbers instead of the data interpreted as characters.
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| wc | Word count - count the lines, words, or characters in files.
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| grep | Global Regular Expression Print - search files for a pattern (the pattern is a regular expression, which another LUG member will present on at some point).
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| sed | Stream Editor - print out a file, but manipulate it in a variety of ways, such as removing lines or performing regular expression substitution, before printing.
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| awk | A mini-programming-language for dealing with "flat-file" databases.
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| tr | Transform - replace certain characters with other characters, or squeeze spaces.
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| split | split a file into several files, each (except for the last) a predetermined size (in lines or bytes).
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| cut | Extract fields from a flat-file database.
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| paste | Join files into a flat-file database by joining corresponding lines with the separator character.
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| join | Join two flat-file databases where a field matches.
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| sort | Sorts input lines.
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| uniq | Unique - squeeze duplicate lines into one. This command only works if the duplicate lines are consecutive, so it's used primarily after sort.
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| diff | Difference - show how two files are different, line-by-line.
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| comm | Compare - compare sorted files based solely on the existence of duplicate lines, rather taking their order into account as well as with diff.
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| man | Manual - get information about a command.
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| apropos | Look up commands about a topic.
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| kill | End a process by sending an appropriate signal (use -9 to guarantee it ending).
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| ps | List running processes.
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| cron | Schedule automatic jobs.
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| nohup | Used as a prefix to a command to indicate that it should keep running after you logout.
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| nice | Affect the priority of a process (you must be root to increase a process's priority, which is decreasing it's nice value).
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| time | Used as a prefix to a command - when the process ends, time reports how much time it took.
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| date | Tells you what time it is.
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| cal | Calendar - displays a calendar.
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| expr | Expression - Evaluate an integer expression.
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| factors | Factor an integer into primes.
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| seq | Sequence - make a sequence from one number to another.
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| bc | Base Calculator - acts as an arbitrary-precision desktop calculator.
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| echo | Print command-line arguments.
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| yes | Prints command-line arguments until yes is aborted.
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| uname | Give you information about your machine and OS.
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| ssh | Secure Shell - connect to a remote host to execute commands on it.
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| netcat | Network Concatenate - send/receive text on arbitrary ports (talk to Andy about this one).
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| wget | Web Get - Save a file from the internet.
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| lynx | A text-mode web browser.
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| stty | Set TTY - set terminal options. TTY is an abbreviation for teletype, and refers to a terminal.
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| clear | Clear the screen (Ctrl-L also works).
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| perl | Python is better (take that, Sam!).
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