"New" Unix/Linux Commands

Here are some more Unix/Linux commands that you need to learn. Remember that you can enter man command to get a complete description of any Unix/Linux command and its options.

Command Description
cal [month #] year Prints a calendar of the specified year. e.g. cal 2010
If a month number is specified, prints only that month. e.g. cal 3 2010 (for March 2010)
cat file1 [file2 ...] Concatenate (join together) specified files and direct the output to the standard output device - the screen.
This command is commonly used to display the contents of one file on the screen. (It's simpler than getting in and out of an editor.)
date Print the current time and date.
who Lists who is logged into a machine. It provides information such as the user's login name and the time when the user logged on.
w Lists who is logged into a machine. Provides information such as the user's login name and the time when the user logged on. It also provides information about what the user is curently doing.
sort Sorts the input stream or the contents of files. To sort the contents of a file, use sort filename.
wc Displays the number of lines, words and characters in a file. To display only the number of lines, you can use wc -l.
file file Perform tests on a file to determine its type. Useful if you want to make sure a file is not an executable before you try to edit it.
cmp file1 file2 Compare two files to see if they are the same. Reports just the first difference unless you specify -l
diff file1 file2 Displays the differences between file1 and file2. This lists the changes necessary to convert file1 to file2.
find path option Search down directories for a file. e.g. find   ./   -name gold.cpp would search in the current directory and in all subdirectories for the file called gold.cpp
grep [option] string [file(s)] Search for a string pattern in a file. There are several options. e.g. grep   namespace *.cpp would search the current directory for the string "namespace" in all .cpp files and show the lines in each file where the string occurs. e.g. grep   -n   namespace *.cpp would perform the same search but also give the line numbers in which the string was found.
ps Lists the processes that are running for a terminal. To see all the processes that are running for you, use ps -fu yourusername. This command is often used with kill.
kill [option] processid Kill the process specified. e.g. kill -9 1455 would perform a "sure kill" (option 9) on process id "1455". This is a handy command if you change your mind after sending a job to the printer and want to delete it from the queue. See the lpq command to see how you can query the print queue for process ids.
lpq -P[printername] Query the specified printer to see active jobs. Reports process ids of jobs. e.g. lpq -Pcl122
quota -v Show how much disk space you are using ("usage") on a multi-user Unix system and what your limit is ("quota"). The numbers given refer to kilobytes of space.