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.
In a line group format, ordinary characters represent themselves; conversion specifications start with ‘%’ and have one of the following forms.
printf
conversion specification and n is one
of the following letters, stands for n's value formatted with F.
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,
and ‘0’ for padding with zeros instead of spaces.
For example, ‘%5dN’ prints the number of new lines in the group
in a field of width 5 characters, using the printf
format "%5d"
.
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 new file) is 0, to ‘1 line’ if N is 1, and to ‘%dN lines’ otherwise.