2.1.7 Other Options

‘--line-buffered’

Use line buffering on output. This can cause a performance penalty.

‘--mmap’

This option is deprecated and now elicits a warning, but is otherwise a no-op. It used to make grep read input with the mmap system call, instead of the default read system call. On modern systems, mmap would rarely if ever yield better performance.

‘-U’

‘--binary’

Treat the file(s) as binary. By default, under MS-DOS and MS-Windows, grep guesses the file type by looking at the contents of the first 32kB read from the file. If grep decides the file is a text file, it strips the CR characters from the original file contents (to make regular expressions with ^ and $ work correctly). Specifying ‘-U’ overrules this guesswork, causing all files to be read and passed to the matching mechanism verbatim; if the file is a text file with CR/LF pairs at the end of each line, this will cause some regular expressions to fail. This option has no effect on platforms other than MS-DOS and MS-Windows.

‘-z’

‘--null-data’

Treat the input as a set of lines, each terminated by a zero byte (the ASCII NUL character) instead of a newline. Like the ‘-Z’ or ‘--null’ option, this option can be used with commands like ‘sort -z’ to process arbitrary file names.

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