Basic UNIX OLC Training

Shells A shell is how you primarily act with the operating system at the command line Two main types of shells: Bourne shell & C shell Modern variants are Bourne Again Shell (bash) and trusted c shell (tcsh) Athena uses tcsh; most everything will be in tcsh syntax. If bash is different, it will be noted

Commands Most UNIX commands are of the form: command -option argument Options (occasionally called 'flags') change the behavior of a command are usually preceded with one or two dashes Arguments are the “input” to the command Commands can take anywhere from 0 to n arguments and options.

Example Command with no options or arguments athena% renew Command with 2 arguments and no options athena% attach consult cref Command with one option and no arguments: athena% znol -l

Shell & Environment Variables Contain information about working environment Change behavior of various programs Change behavior of shell Environment variables apply to your login session Shell variables apply to one instance of your shell (ie: an xterm or gnome-terminal)

Environment Variables Display all environment variables: printenv Display a single variable printenv USER echo $USER Set a variable Tcsh: setenv FOO bar Bash: export FOO=bar

Shell variables Display all variables: set Display a single variable: echo $prompt Set a variable: Tcsh: set foo=bar Bash: foo=bar

I/O Redirection Command > filename Redirect output of command to new file “filename” Command >> filename Append output of command to new file “filename” command < filename read input from file called “filename” command | command2 take the output of command and make it the input of command 2

Examples ls > /tmp/files.txt ls Public >>/tmp/files.txt ls | more sort < /tmp/files.txt

Basic Commands Move file1 into the directory directoryname mv file1 directoryname Copy file1 to the directory directoryname cp file1 directoryname Go back/up one level cd .. Create the directory directoryname mkdir directoryname Restore the previously deleted file file1 undelete file1 Mark file1 for deletion, will be deleted in 3 days delete file1 Move (rename) file1 to a new file called file2 mv file1 file2 Copy file1 to a new file called file2 cp file1 file2 Change current directory to directoryname cd directoryname Show name of current directory pwd List contents of current directory ls

Other Commands Display contents of a file cat filename.txt Count lines in a file: wc -l filename.txt (-c for characters) Display only the beginning or end of a file head filename.txt tail filename.txt

grep grep is a “searching” utility it matches patterns (“regular expressions”) Can do lots of complex things, but simple text search is the best grep dog animals.txt ls | grep thesis grep -i causes it to be case-insensitive

sort Sorts the input and displays it sort -n will sort numerically otherwise it goes 1, 10, 2, 3, 34, 4, etc.

Pagers A pager allows you see one “page” of information at a time Common pagers are “more” and “less” Basic pager commands: space = page down enter = line down b = page up y = line up / = search q = quit

Examples ls | more less mydocument.txt

Shell Wildcards * Match anywhere from 0 to n characters ? match one character Examples: ls foo* will list “foo”, “foo2”, “foobar” ls foo? will only list “foo2”

Manual Pages man commandname whatis commandname apropos <search term> Some commands don't have man pages (ie: fs) Try -help, --help, -?, -h Google

File Permissions ls -l shows file permissions -rw------- 1 jdreed mit 684 Sep 12 09:51 /tmp/tkt_p16901 10 columns. First is – if it's a file, “d” if it's a directory Remaining 9 are 3 groups of 3. First group for user (u), 2nd group for group (g), 3rd group for “everyone else” (o)

File modes r = read (or list files, if directory) w = write (or delete/create if directory) x = execute (or access if directory) s = run as though you were the owner t = sticky (on directory, regardless of permissions files can only be accessed by the owner or root)

chmod change the mode of a file: chmod go-rwx myfile remove read write and execute for group and other chmod u+w myfile Give yourself (owner) ability to write to file On AFS, only the user (u) permissions are used, group and other are ignored, as they are governed by AFS permissions

Jobs and Processes ps show processes in current shell ps -u show all your processes ps ax (or ps -ef) show all processes on the machine

Foreground and Background All processes are run in the foreground by default ie: you start xcluster, you don't get your athena prompt back until it's done Add an & to the end of the command to run in the background To background an already running process Ctrl-Z to suspend it bg to background it

jobs The jobs command can give you a list of suspended and running jobs fg and bg take “%n” as an arugment, where n is the number of the job as shown by “jobs”

killing processes kill can take a job number (from 'jobs') or a process id (from ps) kill -9 can kill off more stubborn processes Don't use it unless kill doesn't work

Unix Utilities df Lists free space on filesystem du shows disk usage – ideal for finding large files in your home directory file attempts to identify a file's contents