‘grep’命令有什么作用？
我想学习如何使用它，以便我可以开始更多地使用终端。
grep用于从文件或其他命令的输出中搜索文本。 它可以返回找到匹配的行或不返回的行。
名称
grep, egrep, fgrep - print lines matching a pattern
概要
grep [options] PATTERN [FILE...] grep [options] [-e PATTERN | -f FILE] [FILE...]
描述
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 addition, two variant programs egrep and fgrep are available. Egrep is the same as grep -E. Fgrep is the same as grep -F.
OPTIONS
-A NUM, --after-context=NUM Print NUM lines of trailing context after matching lines. Places a line containing -- between contiguous groups of matches. -a, --text Process a binary file as if it were text; this is equivalent to the --binary-files=text option. -B NUM, --before-context=NUM Print NUM lines of leading context before matching lines. Places a line containing -- between contiguous groups of matches. -C NUM, --context=NUM Print NUM lines of output context. Places a line containing -- between contiguous groups of matches. -b, --byte-offset Print the byte offset within the input file before each line of output. --binary-files=TYPE If the first few bytes of a file indicate that the file contains binary data, assume that the file is of type TYPE. By default, TYPE is binary, and grep normally outputs either a one-line mes- sage saying that a binary file matches, or no message if there is no match. If TYPE is without-match, grep assumes that a binary file does not match; this is equivalent to the -I option. If TYPE is text, grep processes a binary file as if it were text; this is equivalent to the -a option. Warning: grep --binary-files=text might output binary garbage, which can have nasty side effects if the output is a terminal and if the termi- nal driver interprets some of it as commands. --colour[=WHEN], --color[=WHEN] Surround the matching string with the marker find in GREP_COLOR environment variable. WHEN may be 'never', 'always', or 'auto' -c, --count Suppress normal output; instead print a count of matching lines for each input file. With the -v, --invert-match option (see below), count non-matching lines. -D ACTION, --devices=ACTION If an input file is a device, FIFO or socket, use ACTION to pro- cess it. By default, ACTION is read, which means that devices are read just as if they were ordinary files. If ACTION is skip, devices are silently skipped. -d ACTION, --directories=ACTION If an input file is a directory, use ACTION to process it. By default, ACTION is read, which means that directories are read just as if they were ordinary files. If ACTION is skip, direc- tories are silently skipped. If ACTION is recurse, grep reads all files under each directory, recursively; this is equivalent to the -r option. -E, --extended-regexp Interpret PATTERN as an extended regular expression (see below). -e PATTERN, --regexp=PATTERN Use PATTERN as the pattern; useful to protect patterns beginning with -. -F, --fixed-strings Interpret PATTERN as a list of fixed strings, separated by new- lines, any of which is to be matched. -P, --perl-regexp Interpret PATTERN as a Perl regular expression. -f FILE, --file=FILE Obtain patterns from FILE, one per line. The empty file con- tains zero patterns, and therefore matches nothing. -G, --basic-regexp Interpret PATTERN as a basic regular expression (see below). This is the default. -H, --with-filename Print the filename for each match. -h, --no-filename Suppress the prefixing of filenames on output when multiple files are searched. --help Output a brief help message. -I Process a binary file as if it did not contain matching data; this is equivalent to the --binary-files=without-match option. -i, --ignore-case Ignore case distinctions in both the PATTERN and the input files. -L, --files-without-match Suppress normal output; instead print the name of each input file from which no output would normally have been printed. The scanning will stop on the first match. -l, --files-with-matches Suppress normal output; instead print the name of each input file from which output would normally have been printed. The scanning will stop on the first match. -m NUM, --max-count=NUM Stop reading a file after NUM matching lines. If the input is standard input from a regular file, and NUM matching lines are output, grep ensures that the standard input is positioned to just after the last matching line before exiting, regardless of the presence of trailing context lines. This enables a calling process to resume a search. When grep stops after NUM matching lines, it outputs any trailing context lines. When the -c or --count option is also used, grep does not output a count greater than NUM. When the -v or --invert-match option is also used, grep stops after outputting NUM non-matching lines. --mmap If possible, use the mmap(2) system call to read input, instead of the default read(2) system call. In some situations, --mmap yields better performance. However, --mmap can cause undefined behavior (including core dumps) if an input file shrinks while grep is operating, or if an I/O error occurs. -n, --line-number Prefix each line of output with the line number within its input file. -o, --only-matching Show only the part of a matching line that matches PATTERN. --label=LABEL Displays input actually coming from standard input as input com- ing from file LABEL. This is especially useful for tools like zgrep, eg gzip -cd foo.gz |grep -H --label=foo something --line-buffered Use line buffering, it can be a performance penality. -q, --quiet, --silent Quiet; do not write anything to standard output. Exit immedi- ately with zero status if any match is found, even if an error was detected. Also see the -s or --no-messages option. -R, -r, --recursive Read all files under each directory, recursively; this is equiv- alent to the -d recurse option. --include=PATTERN Recurse in directories only searching file matching PATTERN. --exclude=PATTERN Recurse in directories skip file matching PATTERN. -s, --no-messages Suppress error messages about nonexistent or unreadable files. Portability note: unlike GNU grep, traditional grep did not con- form to POSIX.2, because traditional grep lacked a -q option and its -s option behaved like GNU grep's -q option. Shell scripts intended to be portable to traditional grep should avoid both -q and -s and should redirect output to /dev/null instead. -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-Win- dows. -u, --unix-byte-offsets Report Unix-style byte offsets. This switch causes grep to report byte offsets as if the file were Unix-style text file, ie with CR characters stripped off. This will produce results identical to running grep on a Unix machine. This option has no effect unless -b option is also used; it has no effect on platforms other than MS-DOS and MS-Windows. -V, --version Print the version number of grep to standard error. This ver- sion number should be included in all bug reports (see below). -v, --invert-match Invert the sense of matching, to select non-matching lines. -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 con- stituent 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. -y Obsolete synonym for -i. -Z, --null Output a zero byte (the ASCII NUL character) instead of the character that normally follows a file name. For example, grep -lZ outputs a zero byte after each file name instead of the usual newline. This option makes the output unambiguous, even in the presence of file names containing unusual characters like newlines. This option can be used with commands like find -print0, perl -0, sort -z, and xargs -0 to process arbitrary file names, even those that contain newline characters.
消息来源：为 GREP设计
您可以通过键入来了解命令
info
在终端。
您使用grep标记标记了您的问题。 但是如果你首先阅读引用grep的标签信息会更好：
grep是一个命令行实用程序，用于从标准输入或特定表达式的文件中搜索文本，返回匹配发生的行。
grep一个常见用途是从日志文件或程序输出中找到并打印出某些行。有关如何使用
grep更多信息，请参阅此Ubuntu文档页面 。
此外，几乎任何命令都有一个手册页，您可以阅读它。 在您的情况下，使用此命令：
man grep
更重要的是，您可以使用以下命令之一获取有关grep的信息： info grep ， grep -h ， grep --help ， whatis grep或apropos grep 。
grep根据正则表达式搜索文件的内容。 使用它的最简单的方法是像grep "word" file.txt ，在这种情况下，它将返回file.txt中出现“word”的每一行（如果不存在则不返回任何内容）。 要使它做更高级的事情，请了解正则表达式。 您可以通过搜索在线找到大量教程。 http://lmgtfy.com/?q=grep+tutorial
就个人而言，我不建议仅仅为了使用终端而使用终端。 您可能会遇到很多麻烦来学习像grep这样的复杂工具，只是为了发现您使用您喜欢的解释语言编写的图形程序或脚本。 大多数推荐学习老式终端命令的人都是老式的黑客。
grep命令在一个或多个输入文件中搜索包含与指定模式匹配的行。 默认情况下，grep打印匹配的行。
对于包含与给定PATTERN匹配的行，Grep搜索指定的输入FILE（或标准输入，如果没有命名文件，或者给出文件名）。 默认情况下，grep打印匹配的行。
此外，还有两个变体程序egrep和fgrep。 Egrep与grep -E相同。 Fgrep与grep -F相同。 男人页
你也可以看看SS64