Appendix A: Command Classification

This appendix is a guide to the common standard commands. They are organized in the following tables:

Table A-1: File Management Commands
Command	Description
chgrp	Changes a file's group
chmod	Changes a file's permissions
chown	Changes a file's user ownership
cp	Copies a file
dd	Converts and copies
df	Displays disk usage statistics
du	Displays directory space usage
file	Identifies a file type
find	Searches for a file
ln	Creates a symbolic or hard link
ls	Lists files
mkdir	Creates a directory
mkfifo	Creates a named pipe
mknod	Creates a special file
mv	Renames or moves a file
rm	Removes a file
touch	Creates a file or updates a file's timestamp

Table A-2: Text Processing and Scripting Commands
Command	Description
awk	The awk general-purpose text processing language
basename	Strips extensions and directories from filenames
cat	Displays and concatenates files
cmp	Compares binary files
cut	Extracts columns of lines
diff	Compares text files
dirname	Extracts the directory from a filename
echo	Prints text
ed	A classic line-based text editor
egrep	Extended grep
ex	A newer line-based text editor
expr	Evaluates a mathematical expression
false	Returns a nonzero exit code
fmt	Breaks long lines and reformats text
grep	Searches for lines matching a regular expression
groff	A multi-purpose typesetting utility
head	Displays the first lines of a file
ispell	A spelling checker
less	Displays a text file
more	Displays a text file
nroff	Formats roff documents for text display
patch	Incorporates changes into files; the opposite of diff
perl	A general-purpose scripting language
sed	A stream editor
sort	Sorts lines in a file
split	Chops a file into pieces
tail	Displays the last lines of a file
tee	Duplicates a file stream
test	([) Checks a condition
tr	Translates (or substitutes) characters
true	Returns an exit code of 0 (true)
uniq	Removes duplicate adjacent lines
vi	A visual full-screen editor
wc	Counts words, lines, and characters in a file
xargs	Executes a command repeatedly with arguments from the input stream

Table A-3: Online Documentation Commands
Command	Description
info	Displays GNU-style documentation
man	Displays the traditional Unix online manual

Table A-4: Process and System Utility Commands
Command	Description
at	Runs a program at a certain time
chfn	Changes finger information
chsh	Changes shells
crontab	Runs a periodic job
groups	Shows group membership
id	Shows the current user ID
kill	Sends a signal to a process
logger	Records a message to the system logger
login	Allows a user to login
lsof	Lists open files and other information
mount	Attaches a filesystem to a directory tree
newgrp	Changes the current default group
nice	Runs a process with a suggested priority
passwd	Changes a password
printenv	Prints environment variables
ps	Displays processes
renice	Changes the suggested priority for a process
reset	Attempts to reset the terminal
strace	Traces system calls
su	Switches users
sync	Writes kernel buffers to disk
time	Displays how much processor and system time a process takes
top	Shows the processes with the most resource consumption
umount	Detaches a filesystem from a directory tree

Table A-5: System Information Commands
Command	Description
arch	Displays the system architecture
df	Displays disk usage statistics
dmesg	Displays buffered kernel messages
finger	Displays user information
free	Displays free memory statistics
hostname	Displays the current host's name
last	Shows the last users who logged in
tty	Displays the current terminal name
uptime	Displays system load and how long the system has been running
vmstat	Displays virtual memory statistics
uname	Displays kernel identification information
w	Displays uptime information and current users
who	Displays current users
whoami	Displays the current user

Table A-6: Archival and Compression Commands
Command	Description
bunzip2	A decompression program
bzip2	A decompression program
cpio	An archival program
gunzip	A decompression program
gzip	A compression program
tar	An archival program
uncompress	A decompression program
unshar	A de-archival program
uudecode	A decoding program (the counterpart of uuencode)
uuencode	Encodes binary file into a text file
zcat	Decompresses into a file stream

Table A-7: Miscellaneous Utility Commands
Command	Description
bc	A simple calculator
cal	Shows a calendar
date	Displays the current date
dc	Runs the RPN calculator
pwd	Prints the working directory
script	Starts a shell where all output is recorded in a file
sleep	Pauses for a specified number of seconds
strings	Attempts to show any text embedded in a binary file
yes	Prints an endless stream of lines
which	Displays the first matching program in the current path

Table A-8: Development Commands
Command	Description
ar	A library archiver
as	An assembler
c++	A C++ compiler
cc	A C compiler
cpp	A C preprocessor
g++	A C++ compiler (see c++)
gcc	A C compiler (see cc)
gdb	The GNU debugger
install	Copies a file into a location with certain parameters
ld	linker
ldd	Displays dynamic libraries
make	A package-building tool
perl	A general-purpose scripting language