SU and UNIX

You need not learn a special seismic language to use SU. If you know how to use UNIX shell-redirecting and pipes, you are ready to start using SU--the seismic commands and options can be used just as you would use the built-in UNIX commands. In particular, you can write ordinary UNIX shell scripts to combine frequent command combinations into meta-commands (i.e., processing flows). These scripts can be thought of as ``job files.''

Table 8.1: UNIX Symbols

process1 $<$ file1	process1 takes input from file1
process2 $>$ file2	process2 writes on (new) file2
process3 $»$ file3	process3 appends to file3
process4 $\vert$ process5	output of process4 is input to process5
process6 $«$ text	take input from following lines

So let's begin with a capsule review of the basic UNIX operators as summarized in Table 8.1. The symbols $<$, $>$, and $»$ are known as ``redirection operators,'' since they redirect input and output into or out of the command (i.e., process). The symbol $\vert$ is called a ``pipe,'' since we can picture data flowing from one process to another through the ``pipe.'' Here is a simple SU ``pipeline'' with input ``indata'' and output ``outdata'':

sufilter f=4,8,42,54 <indata |
sugain tpow=2.0 >outdata

This example shows a band-limiting operation being ``piped'' into a gaining operation. The input data set indata is directed into the program sufilter with the < operator, and similarly, the output data set outdata receives the data because of the > operator. The output of sufilter is connected to the input of sugain by use of the | operator.

The strings with the = signs illustrate how parameters are passed to SU programs. The program sugain receives the assigned value 2.0 to its parameter tpow, while the program sufilter receives the assigned four component vector to its parameter f. To find out what the valid parameters are for a given program, we use the self-doc facility.

By the way, space around the UNIX redirection and pipe symbols is optional--the example shows one popular style. On the other hand, spaces around the = operator are not permitted.

The first four symbols in Table 8.1 are the basic grammar of UNIX; the final $«$ entry is the symbol for the less commonly used ``here document'' redirection. Despite its rarity in interactive use, SU shell programs are significantly enhanced by appropriate use of the $«$ operator--we will illustrate this below.

Many built-in UNIX commands do not have a self-documentation facility like SU's--instead, most do have ``man'' pages. For example,

% man cat

CAT(1)              UNIX Programmer's Manual               CAT(1)



NAME
     cat - catenate and print

SYNOPSIS
     cat [ -u ] [ -n ] [ -s ] [ -v ] file ...

DESCRIPTION
     Cat reads each file in sequence and displays it on the stan-
     dard output.  Thus

                    cat file

     displays the file on the standard output, and

                    cat file1 file2 >file3
--More--

You need to know a bit more UNIX lore to use SU efficiently--we'll introduce these tricks of the trade in the context of the examples discussed later in this chapter.