2.1.2 Matching Control

‘-e pattern’

‘--regexp=pattern’

Use pattern as the pattern. This can be used to specify multiple search patterns, or to protect a pattern beginning with a ‘-’. (‘-e’ is specified by POSIX.)

‘-f file’

‘--file=file’

Obtain patterns from file, one per line. The empty file contains zero patterns, and therefore matches nothing. (‘-f’ is specified by POSIX.)

‘-i’

‘-y’

‘--ignore-case’

Ignore case distinctions, so that characters that differ only in case match each other. Although this is straightforward when letters differ in case only via lowercase-uppercase pairs, the behavior is unspecified in other situations. For example, uppercase “S” has an unusual lowercase counterpart “ſ” (Unicode character U+017F, LATIN SMALL LETTER LONG S) in many locales, and it is unspecified whether this unusual character matches “S” or “s” even though uppercasing it yields “S”. Another example: the lowercase German letter “ß” (U+00DF, LATIN SMALL LETTER SHARP S) is normally capitalized as the two-character string “SS” but it does not match “SS”, and it might not match the uppercase letter “ẞ” (U+1E9E, LATIN CAPITAL LETTER SHARP S) even though lowercasing the latter yields the former.

‘-y’ is an obsolete synonym that is provided for compatibility. (‘-i’ is specified by POSIX.)

‘-v’

‘--invert-match’

Invert the sense of matching, to select non-matching lines. (‘-v’ is specified by POSIX.)

‘-w’

‘--word-regexp’

Select only those lines containing matches that form whole words. The test is that the matching substring must either be at the beginning of the line, or preceded by a non-word constituent character. Similarly, it must be either at the end of the line or followed by a non-word constituent character. Word-constituent characters are letters, digits, and the underscore.

‘-x’

‘--line-regexp’

Select only those matches that exactly match the whole line. (‘-x’ is specified by POSIX.)

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