Basic UNIX Commands

This file contains a few basic UNIX commands to enable you to create directories and files, move around to find specific files, and run a few simple commands.

General

passwd

change my password (on some systems it is yppasswd or something different, so ask around)

man

read the manual page, e.g.,

man chmod	read about the UNIX chmod command
man man	read about the man command
man fopen	read about the Standard C library fopen command

Directories and Files

General information about file names

Absolute pathname:

Fully specifies a directory, starting at the root. For example, /home/www/CS400/index.html is an absolute pathname. Absolute pathnames always start with / (which is the name of the root directory), with one exception: a tilde in front of a username represents the absolute pathname of that user's home directory. For example, ~abrady/ProgLang is an absolute name because the system will expand ~abrady to /home/abrady.

Relative pathname:

the name of a file or directory relative to the current directory; e.g.,

myfile.c	file in current directory
progLang/myfile.c	file in progLang directory, which is a subdirectory of the current directory
../myfile.c	file in parent directory (.. means directory above current directory)
../progLang/myfile.c	file in progLang directory, which is at same level in hierarchy as the current directory (it is a child of my parent directory)

Commands for files and directories

Moving Around the Directory Hierarchy

pwd

show me where I am (print working directory)

cd dirname

change to directory dirname, e.g., cd ProgLang or cd ../ProgLang or cd ~abrady/ProgLang

Creating and Removing Directories

mkdir dirname

make a subdirectory under the current directory; call it dirname

rmdir dirname

remove the directory named dirname (must be empty)

Listing Files in a Directory

ls

list the files in the directory (does not include files whose names start with a dot, e.g., .profile, which are also known as hidden files)

ls -aF

better looking listing; lists all files (including dot files), indicating directories, executables and links

ls *.html *.c

only list files ending in .html or .c

Moving, Copying, and Removing Files

mv oldname newname

rename file oldname to newname

mv oldname ProgLang/newname

move file oldname to directory ProgLang, giving it name newname

cp oldfile newfile

make a copy of oldfile, calling the copy newfile

cp oldfile ProgLang/newfile

make a copy of oldfile; put in the ProgLang directory

rm filename

remove filename (does not ask you to confirm this!)

rm *

remove all the files in the directory (don't do this!)

Looking at the Contents of Files

cat filename

display filename to the screen (cat = concatenate)

cat f1 f2 >f3

concatenate f1 and f2, calling combination f3

more filename

display filename to screen one page at a time (use spacebar to go to next page; b to back up)

lpr filename

print a file (pr filename on some systems)

vi filename

edit filename (but learning vi is another lesson!)

emacs filename

edit filename (but learning emacs is another lesson!)

Looking for a Specific Word or Phrase in One or More Files

grep string *.c

find which .c files contain string, e.g., grep fcn3 *.c

Compiling Programs

cc, CC

C and C++ compilers

gcc, g++

GNU C and C++ compilers

gcc -Wall -Wextra -Wpedantic -Wformat -Wshadow -Wredundant-decls -Wstrict-prototypes

The -W options generate warnings about questionable constructions; these sometimes indicate programmer confusion or actual logic errors. (You can also use -Wtraditional to catch some non-traditional C constructs that GCC allows, or -Wmissing-prototypes to find functions that do not have prototypes in header files.)

cflow, dbx, gdb

for C debugging; different debuggers have been available on different systems

Others that might be useful (see man page for details):

chmod

change the permissions on a file or directory

head

display the top few lines of a file

tail

display the last few lines of a file

Other handy, simple commands:

banner word

make a word big

cal

show a calendar, e.g., cal 9 1752

clear

clear the screen

date

show the date and time

echo

print to screen, e.g., echo Hi! or echo $PATH

exit, logout

exit a UNIX shell, log out of UNIX

wc

word count (also counts lines and characters) e.g., wc myfile or wc -l myfile

who

who is logged in to the system

More powerful commands that might be useful (see man page for details):

type command

where/what is command? (could be a command or an alias) e.g., type diff or type l

whereis command

where does this UNIX command live? e.g., whereis man

grep

look for a pattern in file(s), e.g., grep pat myfile

diff

show differences between two files, e.g., diff old new

sort

sort and collate lines of a file

find

find files by name or other characteristics

ftp

file transfer protocol

ssh

remote login (secure shell)

scp

secure copy (remote file copy); uses ssh

ps

show process status of running processes

kill

kill a process, e.g., kill -9 14238