1.官方简介
grep是linux的常用命令，用于对文件和文本执行重复搜索任务的unix工具，可以通过grep命令指定特定搜索条件来搜索文件及其内容以获取有用的信息。
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usage: grep [option]... pattern [file]...
search for pattern in each file or standard input.
pattern is, by default, a basic regular expression (bre).
example: grep -i 'hello world' menu.h main.c
regexp selection and interpretation:
-e, --extended-regexp pattern is an extended regular expression (ere)
-f, --fixed-strings pattern is a set of newline-separated fixed strings
-g, --basic-regexp pattern is a basic regular expression (bre)
-p, --perl-regexp pattern is a perl regular expression
-e, --regexp=pattern use pattern for matching
-f, --file=file obtain pattern from file
-i, --ignore-case ignore case distinctions
-w, --word-regexp force pattern to match only whole words
-x, --line-regexp force pattern to match only whole lines
-z, --null-data a data line ends in 0 byte, not newline
miscellaneous:
-s, --no-messages suppress error messages
-v, --invert-match select non-matching lines
-v, --version display version information and exit
--help display this help text and exit
output control:
-m, --max-count=num stop after num matches
-b, --byte-offset print the byte offset with output lines
-n, --line-number print line number with output lines
--line-buffered flush output on every line
-h, --with-filename print the file name for each match
-h, --no-filename suppress the file name prefix on output
--label=label use label as the standard input file name prefix
-o, --only-matching show only the part of a line matching pattern
-q, --quiet, --silent suppress all normal output
--binary-files=type assume that binary files are type;
type is 'binary', 'text', or 'without-match'
-a, --text equivalent to --binary-files=text
-i equivalent to --binary-files=without-match
-d, --directories=action how to handle directories;
action is 'read', 'recurse', or 'skip'
-d, --devices=action how to handle devices, fifos and sockets;
action is 'read' or 'skip'
-r, --recursive like --directories=recurse
-r, --dereference-recursive
likewise, but follow all symlinks
--include=file_pattern
search only files that match file_pattern
--exclude=file_pattern
skip files and directories matching file_pattern
--exclude-from=file skip files matching any file pattern from file
--exclude-dir=pattern directories that match pattern will be skipped.
-l, --files-without-match print only names of files containing no match
-l, --files-with-matches print only names of files containing matches
-c, --count print only a count of matching lines per file
-t, --initial-tab make tabs line up (if needed)
-z, --null print 0 byte after file name
context control:
-b, --before-context=num print num lines of leading context
-a, --after-context=num print num lines of trailing context
-c, --context=num print num lines of output context
-num same as --context=num
--group-separator=sep use sep as a group separator
--no-group-separator use empty string as a group separator
--color[=when],
--colour[=when] use markers to highlight the matching strings;
when is 'always', 'never', or 'auto'
-u, --binary do not strip cr characters at eol (msdos/windows)
-u, --unix-byte-offsets report offsets as if crs were not there
(msdos/windows)
'egrep' means 'grep -e'. 'fgrep' means 'grep -f'.
direct invocation as either 'egrep' or 'fgrep' is deprecated.
when file is -, read standard input. with no file, read . if a command-line
-r is given, - otherwise. if fewer than two files are given, assume -h.
exit status is 0 if any line is selected, 1 otherwise;
if any error occurs and -q is not given, the exit status is 2.
report bugs to: bug-grep@gnu.org
gnu grep home page: <http://www.gnu.org/software/grep/>
general help using gnu software: http://www.gnu.org/gethelp/
我平时也是简单的查看一个用户数据，用于简单的数据校对，最近突然接到分析后台日志的需求，才发现grep用处还是不少的。
比如我们后台日志相当大，要是直接从服务器直接拉取，耗时长占用带宽，所以方案就是直接使用 grep关键字重定向到新的文件中，从14g直接到12m,然后再数据清洗和分析。
2.实战介绍
2.1使用grep命令对多文件中多种文本查询
note :使用egrep命令，可使用扩展的正则表达式
1.多文件
2.多文本 ， 关系是or
例如下面对 对文件中 存在关键字 worda or wordb进行提取:
grep 'worda\|wordb' *.py grep -e 'worda|wordb' *.doc grep -e worda -e wordb *.py egrep "worda|wordb" *.c
3.多文本关系是 and
这里我并没有看到 直接能用的【option】,只能加一层管道符|。
例如：
grep -e pattern1 *.py |grep -e pattern2
2.2完全匹配关键词 -w
grep -w 'warning\|error\|critical' /home/logs
2.3使用-i参数忽略大小写，–color高亮显示匹配结果
egrep -wi --color 'warning|error|critical' /home/logs
2.4递归查找
egrep -rwi --color 'warning|error' /home/logs/
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