Contents of the DIFF.DOC file
diff - differential file comparer
diff [ -befh ] file1 file2
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(1) commands to convertfile1 into
file2.The numbers after the letters pertain to file2. By
exchanging a for d and reading backward, conversion of file2
into file1 is given. 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 thatare
affected in the first file flagged by <, then all the lines
that are affected in the second file flagged by >.
Except in rare circumstances, diff finds a smallest suffi-
cient set of file differences.
-b Cause trailing blanks (spaces and tabs) tobe ignored
and other strings of blanks to compare equal.
-e Produce a script of a, c, and d commands for the editor
ed, which recreates file2 from file1.
-f Produce a similar script, not useful with ed, inthe
In connection with -e, the following shell programcan
help maintain multiple versionsof 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
-h Does a fast, but incomplete job. It works only when
changed parts are short and well separated. Options -e
and -f are unavailable with -h.
% cat list1 % cat list2
% diff list1 list2
Exit status is 0 for no differences, 1 for some, 2 for trou-
Editing scripts produced under the -eor -foptionare
unable to create lines consisting of a single period (.).
The script file is produced, but it will produce incorrect
results if run under ed.