2.6.2 Line Formats

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.

`--old-line-format=format'

formats lines just from the first file.

`--new-line-format=format'

formats lines just from the second file.

`--unchanged-line-format=format'

formats lines common to both files.

`--line-format=format'

formats all lines; in effect, it sets all three above options simultaneously.

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

`%l'

stands for the contents of the line, not counting its trailing newline (if any). This format ignores whether the line is incomplete; See section 3. Incomplete Lines.

`%L'

stands for the contents of the line, including its trailing newline (if any). If a line is incomplete, this format preserves its incompleteness.

`%%'

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.

`%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, stands for the line number formatted with F. For example, `%.5dn' prints the line number using the printf format "%.5d". See section 2.6.1 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