1. UNIX  Portable (common to many computer architectures), multitasking, multi-user operating system  Introduced by Bell labs in mid-1960’s  Thus, much longer history of serious computing than Windows or Apple OS (Apple OS is practically UNIX)  Stable, secure, high performance  Practically never needs rebooting  Implementations on PC are called Linux  Linux is only the kernel, and numerous packages with graphical interfaces are available  See http://www.linux.com/directory/Distributionshttp://www.linux.com/directory/Distributions  All distributions come with hundreds of free programs  Note LibreOffice, Octave  We use Red Hat Enterprise (this one is not free, but there exists a free equivalent) – good for development, parallel computing  I use Fedora at home (“Cinnamon” is a simple and nice-looking desktop)  Many people love Ubuntu (user- and media-oriented)

2. UNIX shell  Seismic Un*x and GMT rely on the ability of the shell to combine many programs for achieving a common task  Every processing flow in Seismic Un*x and every image in GMT should be described by a shell script  Example of a C shell script doing GMT plotting: #!/bin/csh ########### GMT script to redraw "Aki" plot ###################################################### set PSFILE = PS/aki-1.ps # set REGION = -R55/30/180/65r set REGION = -R0.0/-0.1/25/0.35r set PROJ = "-JX4/3 -P -V" set BLACK =-G0/0/0 set WHITE =-G255/255/255 set GRAY =-G200/200/200 set RED =-G225/0/0 set RUBY =-G225/0/100 set GREEN =-G0/125/0

3. UNIX shell example (cont) set SSIZE = 0.07 set SLINE = -W1.2 set LINE = -W0.7 gmtset BASEMAP_TYPE PLAIN DEGREE_FORMAT 1 GRID_CROSS_SIZE 0 GRID_PEN 0.5\ ANOT_FONT_SIZE 12 LABEL_FONT_SIZE 12 ## plot: psbasemap $REGION $PROJ -Bf1a5:"Frequency (Hz)":/f0.01a0.05:"100/Q":WS -K > $PSFILE psxy $REGION $PROJ $LINE aki-fpac-1.dat -O -K >> $PSFILE psxy $REGION $PROJ $SLINE -Sd$SSIZE aki-fpac-1.dat -O -K >> $PSFILE psxy $REGION $PROJ $LINE aki-fotl-1.dat -O -K >> $PSFILE psxy $REGION $PROJ $SLINE -Sc$SSIZE aki-fotl-1.dat -O -K >> $PSFILE psxy $REGION $PROJ $LINE aki-ftsk-1.dat -O -K >> $PSFILE psxy $REGION $PROJ $SLINE -St$SSIZE $BLACK aki-ftsk-1.dat -O -K >> $PSFILE psxy $REGION $PROJ $LINE aki-fois-1.dat -O -K >> $PSFILE psxy $REGION $PROJ $SLINE -Sx$SSIZE $BLACK aki-fois-1.dat -O >> $PSFILE kghostview $PSFILE &

4. UNIX pipelines and redirection suread | sufilter | suplot # this prints two files on screen: cat file1 file2 # this prints two files into another file3: cat file1 file2 > file3 # this writes into file2 from multiple files file1*.txt # the lines containing both tokens AAAA and BBBB: grep AAAA file1*.txt | grep BBBB > file2

5. Basic commands. # current directory.. # directory one level above ~# HOME directory *, ?, or [a,b,..] # wild cards (filename patterns) man, info# manuals about any programs sh, csh, tcsh# “shell” programs (user dialog) env# displays user environment source# executes shell commands from a file pwd, ls# display directories cd# change working directory more, less, tail# display file contents grep# search file contents for text tokens wc # counts lines, words, and characters awk, se# filters for file (stream) contents cp, rm, mv# copy, remove, rename or move files rmdir# remove (empty) directory gcc, g++, g77, gfortran # compilers make# for compiling code or maintaining documents

6. User environment  Collection of strings “NAME = VALUE” describing the specific user settings  usually created upon login or entering a shell (opening a terminal window)  modified and utilized in shell scripts