= diff: differential file comparator


*diff* [ *-efbwr* ] file1 ... file2


_Diff_ tells what lines must be changed in two files to bring them into
agreement. If one file is a directory, then a file in that directory
with basename the same as that of the other file is used. If both files
are directories, similarly named files in the two directories are
compared by the method of _diff_ for text files and _cmp_(1) otherwise.
If more than two file names are given, then each argument is compared to
the last argument as above. The *-r* option causes _diff_ to process
similarly named subdirectories recursively. The normal output contains
lines of these forms:

* _n1_ *a* _n3,n4_ +
_n1,n2_ *d* _n3_ +
_n1,n2_ *c* _n3,n4_

These lines resemble Plan 9 or Unix _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 *-w* option causes all
white-space to be removed from input lines before applying the
difference algorithm.

The *-e* option produces a script of _a, c_ and _d_ commands for the
Plan 9 or Unix editor _ed_, which will recreate _file2_ from _file1_.
The *-f* option produces a similar script, not useful with _ed_, in the
opposite order. It may, however, be useful as input to a stream-oriented
post-processor.

Except in rare circumstances, _diff_ finds a smallest sufficient set of
file differences.

== FILES

*/tmp/diff[12]*

== SOURCE

*/appl/cmd/diff.b*

== DIAGNOSTICS

Exit status is the empty string for no differences,

for some, and

for trouble.

== SEE ALSO

_cmp_(1)

== BUGS

Editing scripts produced under the *-e* or *-f* option are naive about
creating lines consisting of a single `**.**'. +
When running _diff_ on directories, the notion of what is a text file is
open to debate. +
Nothing directly interprets the _ed_ scripts within the Inferno
environment.