grep/pgrep/egrep/fgrep
Differences between grep, pgrep, egrep, and fgrep (Linux):
grep
grep is an acronym that stands for "Global Regular Expressions Print". grep is a program which scans a specified file or files line by line, returning lines that contain a pattern. A pattern is an expression that specifies a set of strings by interpreting characters as meta-characters. For example the asterisk meta character (*) is interpreted as meaning "zero or more of the preceding element". This enables users to type a short series of characters and meta characters into a grep command to have the computer show us what lines in which files match.
The standard grep command looks like:
grep <flags> '<regular expression>' <filename>
grep prints the search results to the screen (stdout) and returns the following exit values:
0 A match was found.
1 No match was found.
>1 A syntax error was found or a file was inaccessible
(even if matches were found).
Some common flags are: -c
for counting the number of successful matches and not printing the actual matches, -i
to make the search case insensitive, -n
to print the line number before each match printout, -v
to take the complement of the regular expression (i.e. return the lines which don't match), and -l
to print the file names of files with lines which match the expression.
egrep
egrep is an acronym that stands for "Extended Global Regular Expressions Print".
The 'E' in egrep means treat the pattern as a regular expression. "Extended Regular Expressions" abbreviated 'ERE' is enabled in egrep. egrep (which is the same as grep -E
) treats +
, ?
, |
, (
, and )
as meta-characters.
In basic regular expressions (with grep), the meta-characters ?
, +
, {
, |
, (
, and )
lose their special meaning. If you want grep to treat these characters as meta-characters, escape them \?
, \+
, \{
, \|
, \(
, and \)
.
For example, here grep uses basic regular expressions where the plus is treated literally, any line with a plus in it is returned.
grep "+" myfile.txt
egrep on the other hand treats the "+" as a meta character and returns every line because plus is interpreted as "one or more times".
egrep "+" myfile.txt
Here every line is returned because the +
was treated by egrep as a meta character. normal grep would have searched only for lines with a literal +
.
fgrep
fgrep is an acronym that stands for "Fixed-string Global Regular Expressions Print".
fgrep (which is the same as grep -F) is fixed or fast grep and behaves as grep but does NOT recognize any regular expression meta-characters as being special. The search will complete faster because it only processes a simple string rather than a complex pattern.
For example, if I wanted to search my .bash_profile for a literal dot (.) then using grep would be difficult because I would have to escape the dot because dot is a meta character that means 'wild-card, any single character':
grep "." myfile.txt
The above command returns every line of myfile.txt. Do this instead:
fgrep "." myfile.txt
Then only the lines that have a literal '.' in them are returned. fgrep helps us not bother escaping our meta characters.
pgrep
pgrep is an acronym that stands for "Process-ID Global Regular Expressions Print".
pgrep looks through the currently running processes and lists the process IDs which matches the selection criteria to stdout. pgrep is handy when all you want to know is the process id integer of a process. For example, if I wanted to know only the process ID of my mysql process I would use the command pgrep mysql
which would return a process ID like 7312.
来自:http://superuser.com/questions/508881/what-is-the-difference-between-grep-pgrep-egrep-fgrep
grep/pgrep/egrep/fgrep的更多相关文章
- grep, egrep, fgrep笔记
grep, egrep, fgrep grep: 根据模式搜索文本,并将符合模式的文本行显示出来.Pattern: 文本字符和正则表达式的元字符组合而成匹配条件 grep [options] PATT ...
- grep egrep fgrep命令
一.grep.egrep.fgrep命令 本文中主要介绍了linux系统下grep egrep fgrep命令和正则表达式的基本参数和使用格式.方法.(注释:文中fg代表例子,) 1.1.基本定义: ...
- grep与正则表达式,grep、egrep和fgrep
grep用法详解:grep与正则表达式 首先要记住的是: 正则表达式与通配符不一样,它们表示的含义并不相同!正则表达式只是一种表示法,只要工具支持这种表示法, 那么该工具就可以处理正则表达式的字符串. ...
- grep、egrep、fgrep的用法与特性详解
[转载自]http://tanxw.blog.51cto.com/4309543/1361993 开篇 学习Linux也有一段时间了,对Linux多少也算是有点了解了,越是了解也就越对这 ...
- Linux三剑客之grep 与 egrep
grep: Linux上文本处理三剑客 grep:文本过滤(模式:pattern)工具; *(grep, egrep, fgrep) sed:stream editor,文本编辑工具: awk:Lin ...
- linux中grep和egrep的用法
1. grep简介 grep (global search regular expression_r(RE) and print out the line,全面搜索正则表达式并把行打印出来)是一种强大 ...
- Linux正则表达式grep与egrep
grep -io "http:/=[A-Z0-9]\{16\}" ./wsxf.txt >wsxf_urls.txt Linux正则表达式grep与egrep 正则表达式:它 ...
- grep和egrep正则表达式
Linux上文本处理三剑客 grep :文本过滤( 模式:pattern) 工具 grep, egrep, fgrep (不支持正则表达式搜索,但搜索纯文本的数据最快) sed :stream edi ...
- grep、egrep命令用法
何谓正则表达式 正则表达式,又称正规表示法.常规表示法(Regular Expression,在代码中常简写为regex.regexp或RE),是一类字符所书写的模式,其中许多字符不表示其字面意义,而 ...
随机推荐
- .netcore 整合 log4net
1.背景 前两天,曾经的一个同事咨询我,怎样将log4net以中间件的形式整合到core里边去.我不假思索的回答,这种问题应该有人做过吧,他说没有.于是,我去博客园搜了下,发现还真没有,全部都是传统. ...
- redux最佳实践
对于初学者,redux的理念很难理解.其实redux并不难,redux核心理念就是数据仓库,所有数据操作来源都是明确的.只不过不是直接操作数据,而是交给特定的角色做特定的工作,分工明确. pro ...
- Android SDK安装及配置模拟器
环境搭建 1.安装JDK 2.下载Android sdk exe格式和zip格式都可以 3.安装installer_r24.4.1-windows.exe文件,里面有两个应用程序: "SDK ...
- brew装snappy
brew装snappy,我在mac上已经开了socks5代理,也尝试了lantern或者duotai.org,结果都下载不动. 解决方法:把snappy包手动从浏览器下载,然后放到缓存目录,再执行br ...
- 【C++ Primer | 19】嵌套类、局部类
嵌套类 #include <iostream> using namespace std; class c1 { public: int a; void foo(); class c2 { ...
- WCF服务寄宿Windows
windows服务的介绍 Windows服务应用程序是一种需要长期运行的应用程序,它对于服务器环境特别适合.它没有用户界面,并且也不会产生任何可视输出.任何用户消息都会被写进Windows事件日志.计 ...
- 彻底解决:java.sql.SQLException: Incorrect string value: '\xF0\x9F\x92\x94' for column 'name' at row 1
转载:https://blog.csdn.net/qq_31122833/article/details/83992085
- canvas简单下雨特效
前面做了两个简单的效果,这次就来个下雨的效果 思路简单的说一下 随机在屏幕中的位置画雨滴,moveTo(x,y) 雨滴的长度就是lineTo(x,y+len) 每次重新绘制页面,就能达到下雨的效果了 ...
- A. 【UR #4】元旦三侠的游戏
题解: 挺水的吧 会发现当b不等于1的时候,状态只有sigma i x^(1/i) 显然这东西很小.. 然后我们会发现每个点向两个点动 定义必胜点和必败点 当一个点有一条边连向必败点 那么它就是必胜点 ...
- python错误、调试、测试
1.错误, Python内置的try...except...finally用来处理错误十分方便.出错时,会分析错误信息并定位错误发生的代码位置才是最关键的. 程序也可以主动抛出错误,让调用者来处理相应 ...