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。
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
- grep 'pattern' file1 file2
2.多文本 ， 关系是OR
- egrep 'pattern1|pattern2' *.py
- grep -e pattern1 -e pattern2 *.py
- grep -E 'pattern1|pattern2' *.doc
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/