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# (diff.info.gz) Line Group Formats

Info Catalog (diff.info.gz) If-then-else (diff.info.gz) Line Formats

Line Group Formats
------------------

Line group formats let you specify formats suitable for many
applications that allow if-then-else input, including programming
languages and text formatting languages.  A line group format specifies
the output format for a contiguous group of similar lines.

For example, the following command compares the TeX files old' and
new', and outputs a merged file in which old regions are surrounded by
\begin{em}'-\end{em}' lines, and new regions are surrounded by
\begin{bf}'-\end{bf}' lines.

diff \
--old-group-format='\begin{em}
%<\end{em}
' \
--new-group-format='\begin{bf}
%>\end{bf}
' \
old new

The following command is equivalent to the above example, but it is a
little more verbose, because it spells out the default line group
formats.

diff \
--old-group-format='\begin{em}
%<\end{em}
' \
--new-group-format='\begin{bf}
%>\end{bf}
' \
--unchanged-group-format='%=' \
--changed-group-format='\begin{em}
%<\end{em}
\begin{bf}
%>\end{bf}
' \
old new

Here is a more advanced example, which outputs a diff listing with
headers containing line numbers in a "plain English" style.

diff \
--unchanged-group-format='' \
--old-group-format='-------- %dn line%(n=1?:s) deleted at %df:
%<' \
--new-group-format='-------- %dN line%(N=1?:s) added after %de:
%>' \
--changed-group-format='-------- %dn line%(n=1?:s) changed at %df:
%<-------- to:
%>' \
old new

To specify a line group format, use diff' with one of the options
listed below.  You can specify up to four line group formats, one for
each kind of line group.  You should quote FORMAT, because it typically
contains shell metacharacters.

--old-group-format=FORMAT'
These line groups are hunks containing only lines from the first
file.  The default old group format is the same as the changed
group format if it is specified; otherwise it is a format that
outputs the line group as-is.

--new-group-format=FORMAT'
These line groups are hunks containing only lines from the second
file.  The default new group format is same as the changed group
format if it is specified; otherwise it is a format that outputs
the line group as-is.

--changed-group-format=FORMAT'
These line groups are hunks containing lines from both files.  The
default changed group format is the concatenation of the old and
new group formats.

--unchanged-group-format=FORMAT'
These line groups contain lines common to both files.  The default
unchanged group format is a format that outputs the line group
as-is.

In a line group format, ordinary characters represent themselves;
conversion specifications start with %' and have one of the following
forms.

%<'
stands for the lines from the first file, including the trailing
newline.  Each line is formatted according to the old line format
( Line Formats).

%>'
stands for the lines from the second file, including the trailing
newline.  Each line is formatted according to the new line format.

%='
stands for the lines common to both files, including the trailing
newline.  Each line is formatted according to the unchanged line
format.

%%'
stands for %'.

%c'C''
where C is a single character, stands for C.  C may not be a
backslash or an apostrophe.  For example, %c':'' stands for a
colon, even inside the then-part of an if-then-else format, which
a colon would normally terminate.

%c'\O''
where O is a string of 1, 2, or 3 octal digits, stands for the
character with octal code O.  For example, %c'\0'' stands for a
null character.

FN'
where F is a printf' conversion specification and N is one of the
following letters, stands for N's value formatted with F.

e'
The line number of the line just before the group in the old
file.

f'
The line number of the first line in the group in the old
file; equals E + 1.

l'
The line number of the last line in the group in the old file.

m'
The line number of the line just after the group in the old
file; equals L + 1.

n'
The number of lines in the group in the old file; equals L -
F + 1.

E, F, L, M, N'
Likewise, for lines in the new file.

The printf' conversion specification can be %d', %o', %x', or
%X', specifying decimal, octal, lower case hexadecimal, or upper
case hexadecimal output respectively.  After the %' the following
options can appear in sequence: a series of zero or more flags; an
integer specifying the minimum field width; and a period followed
by an optional integer specifying the minimum number of digits.
The flags are -' for left-justification, '' for separating the
digit into groups as specified by the LC_NUMERIC' locale category,
%5dN' prints the number of new lines in the group in a field of
width 5 characters, using the printf' format "%5d"'.

(A=B?T:E)'
If A equals B then T else E.  A and B are each either a decimal
constant or a single letter interpreted as above.  This format
spec is equivalent to T if A's value equals B's; otherwise it is
equivalent to E.

For example, %(N=0?no:%dN) line%(N=1?:s)' is equivalent to no
lines' if N (the number of lines in the group in the the new file)
is 0, to 1 line' if N is 1, and to %dN lines' otherwise.

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Info Catalog (diff.info.gz) If-then-else (diff.info.gz) Line Formats
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