Grep searches the named input FILEs (or standard input if no files are named, or the file name - is given) for lines containing a match to the given PATTERN. By default, grep prints the matching lines. …

The grep utility shall search the input files, selecting lines matching one or more patterns; the types of patterns are controlled by the options specified. The patterns are specified by the -e option, -f option, …

hpux operating system manual for grep section 1 of the unix.com man page documentation.

Man page for grep (1) on opensolaris, from the unix.com online archive.

grep searches for PATTERN in each FILE. A FILE of "-" stands for standard input. If no FILE is given, recursive searches examine the working directory, and nonrecursive searches read standard input. …

Grep patterns are limited regular expressions in the style of ed(1); it uses a compact nondeterministic algorithm. Egrep patterns are full regular expressions; it uses a fast deterministic algorithm that …

Zgrep invokes grep on compressed or gzipped files. All options specified are passed directly to grep. If no file is specified, then the standard input is decompressed if necessary and fed to grep. Otherwise …

grep searches the named input FILEs (or standard input if no files are named, or the file name - is given) for lines containing a match to the given PATTERN. By default, grep prints the matching lines. In …

Man page for xml_grep (1) on centos, from the unix.com online archive.

xzgrep invokes grep(1) on files which may be either uncompressed or compressed with xz(1), lzma(1), gzip(1), or bzip2(1). All options specified are passed directly to grep(1). If no file is specified, then …