Line formats control how each line taken from an input file is output as part of a line group in if-then-else format.
For example, the following command outputs text with a one-character change indicator to the left of the text. The first character of output is ‘-’ for deleted lines, ‘|’ for added lines, and a space for unchanged lines. The formats contain newline characters where newlines are desired on output.
diff \ --old-line-format='-%l ' \ --new-line-format='|%l ' \ --unchanged-line-format=' %l ' \ old new
To specify a line format, use one of the following options. You should quote format, since it often contains shell metacharacters.
In a line format, ordinary characters represent themselves; conversion specifications start with ‘%’ and have one of the following forms.
printfconversion specification, stands for the line number formatted with F. For example, ‘%.5dn’ prints the line number using the
"%.5d". See Line Group Formats, for more about printf conversion specifications.
The default line format is ‘%l’ followed by a newline character.
If the input contains tab characters and it is important that they line up on output, you should ensure that ‘%l’ or ‘%L’ in a line format is just after a tab stop (e.g. by preceding ‘%l’ or ‘%L’ with a tab character), or you should use the -t or --expand-tabs option.
Taken together, the line and line group formats let you specify many different formats. For example, the following command uses a format similar to normal diff format. You can tailor this command to get fine control over diff output.
diff \ --old-line-format='< %l ' \ --new-line-format='> %l ' \ --old-group-format='%df%(f=l?:,%dl)d%dE %<' \ --new-group-format='%dea%dF%(F=L?:,%dL) %>' \ --changed-group-format='%df%(f=l?:,%dl)c%dF%(F=L?:,%dL) %<--- %>' \ --unchanged-group-format='' \ old new