06-15-2017
Thanks for the friendly welcome Don. I haven't had any homework assignments for over 25 years. I'm a hobbyist working on a maths problem. I wrote a little C program to generate this data, and want to sort through it with shell tools as an intermediate step to solving the problem empirically (as a hint to myself, before I try to solve it mathematically). I am using Bash by default, since it is the default shell on my laptop running OS 10.6, but other shells are available. What I have done so far: stared at it and realised I don't know how to do this kind of multi-line search with the handful of shell commands I have taught myself over the last 30 years (and only used very infrequently, when such problems come up). I suppose I could also have tried to do this weeding out within my C program, but I can't see how to do it without having to hold everything in memory all at once (again, I write such programs very infrequently). So, it seems better to write it to a file then use some other tool in the shell to search that file. Hence my posting here. I'm sure there is a better way, but I break out my C and shell scripts about once every 6 months and at my age it's often easier to ask.
Is there anyone less suspicious who might be able to point me in a useful direction?
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DIFF(1) General Commands Manual DIFF(1)
NAME
diff - differential file comparator
SYNOPSIS
diff [ -efbh ] file1 file2
DESCRIPTION
Diff tells what lines must be changed in two files to bring them into agreement. If file1 (file2) is `-', the standard input is used. If
file1 (file2) is a directory, then a file in that directory whose file-name is the same as the file-name of file2 (file1) is used. The
normal output contains lines of these forms:
n1 a n3,n4
n1,n2 d n3
n1,n2 c n3,n4
These lines resemble ed commands to convert file1 into file2. The numbers after the letters pertain to file2. In fact, by exchanging `a'
for `d' and reading backward one may ascertain equally how to convert file2 into file1. As in ed, identical pairs where n1 = n2 or n3 = n4
are abbreviated as a single number.
Following each of these lines come all the lines that are affected in the first file flagged by `<', then all the lines that are affected
in the second file flagged by `>'.
The -b option causes trailing blanks (spaces and tabs) to be ignored and other strings of blanks to compare equal.
The -e option produces a script of a, c and d commands for the editor ed, which will recreate file2 from file1. The -f option produces a
similar script, not useful with ed, in the opposite order. In connection with -e, the following shell program may help maintain multiple
versions of a file. Only an ancestral file ($1) and a chain of version-to-version ed scripts ($2,$3,...) made by diff need be on hand. A
`latest version' appears on the standard output.
(shift; cat $*; echo '1,$p') | ed - $1
Except in rare circumstances, diff finds a smallest sufficient set of file differences.
Option -h does a fast, half-hearted job. It works only when changed stretches are short and well separated, but does work on files of
unlimited length. Options -e and -f are unavailable with -h.
FILES
/tmp/d?????
/usr/lib/diffh for -h
SEE ALSO
cmp(1), comm(1), ed(1)
DIAGNOSTICS
Exit status is 0 for no differences, 1 for some, 2 for trouble.
BUGS
Editing scripts produced under the -e or -f option are naive about creating lines consisting of a single `.'.
DIFF(1)