[root@mufeng test]# grep --help
用法: grep [選項]... PATTERN [FILE]...
在每個 FILE 或是標準輸入中查找 PATTERN。
默認的 PATTERN 是一個基本正則表達式(縮寫為 BRE)。
例如: grep -i 'hello world' menu.h main.c

正則表達式選擇與解釋:
  -E, --extended-regexp     PATTERN 是一個可擴展的正則表達式(縮寫為 ERE)
  -F, --fixed-strings       PATTERN 是一組由斷行符分隔的定長字符串。
  -G, --basic-regexp        PATTERN 是一個基本正則表達式(縮寫為 BRE)
  -P, --perl-regexp         PATTERN 是一個 Perl 正則表達式
  -e, --regexp=PATTERN      用 PATTERN 來進行匹配操作
  -f, --file=FILE           從 FILE 中取得 PATTERN
  -i, --ignore-case         忽略大小寫
  -w, --word-regexp         強制 PATTERN 僅完全匹配字詞
  -x, --line-regexp         強制 PATTERN 僅完全匹配一行
  -z, --null-data           一個 0 字節的數據行，但不是空行

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

輸出控制:
  -m, --max-count=NUM       NUM 次匹配后停止
  -b, --byte-offset         輸出的同時打印字節偏移
  -n, --line-number         輸出的同時打印行號
      --line-buffered       每行輸出清空
  -H, --with-filename       為每一匹配項打印文件名
  -h, --no-filename         輸出時不顯示文件名前綴
      --label=LABEL         將LABEL 作為標準輸入文件名前綴
  -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

文件控制:
  -B, --before-context=NUM  打印以文本起始的NUM 行
  -A, --after-context=NUM   打印以文本結尾的NUM 行
  -C, --context=NUM         打印輸出文本NUM 行
  -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)

[root@mufenggrow ~]# grep ^root /etc/passwd
root:x:0:0:root:/root:/bin/bash

[root@mufenggrow ~]# grep "root" /etc/passwd
root:x:0:0:root:/root:/bin/bash
operator:x:11:0:operator:/root:/sbin/nologin
[root@mufenggrow ~]# 

root@mufenggrow ~]# echo root >> a.txt
[root@mufenggrow ~]# echo root >> b.txt
[root@mufenggrow ~]# grep "root" /etc/passwd  a.txt b.txt
/etc/passwd:root:x:0:0:root:/root:/bin/bash
/etc/passwd:operator:x:11:0:operator:/root:/sbin/nologin
a.txt:root
b.txt:root
[root@mufenggrow ~]# 

[root@mufenggrow ~]# cp /etc/passwd ./
## 源文件一共35行
[root@mufenggrow ~]# cat /etc/passwd |wc -l
35
## 追加空行進去
[root@mufenggrow ~]# echo "" >> /etc/passwd
[root@mufenggrow ~]# cat /etc/passwd |wc -l
36
## 去掉空行測試
[root@mufenggrow ~]# grep -v ^$  /etc/passwd |wc -l
35
[root@mufenggrow ~]# 

[root@mufenggrow ~]# grep -v ^# passwd |wc -l
35

[root@mufenggrow ~]# grep root /etc/passwd  --color=auto
root:x:0:0:root:/root:/bin/bash
operator:x:11:0:operator:/root:/sbin/nologin
[root@mufenggrow ~]# 

[root@mufenggrow ~]# grep -o root /etc/passwd
root
root
root
root

[root@mufenggrow ~]# grep -n "root" passwd
1:root:x:0:0:root:/root:/bin/bash
11:operator:x:11:0:operator:/root:/sbin/nologin

root@mufenggrow ~]# grep -n "" passwd |awk -F : '{print $1}' |tail -n 1
35

[root@mufenggrow ~]# grep -c "root" passwd
2

[root@mufenggrow ~]# grep -c "$" passwd
35