【Linux】三剑客命令之grep命令的常见用法

Linux三剑客指的是grep、sed、awk这三个命令。其中grep命令的详细用法有很多但这里只介绍了常见用法本文最后也贴了该命令的帮助文档以供查阅。

1. grep 可用于查找文件里符合条件的字符串

[root@localhost ~]# cat hello.txt 
Hello world!
Hello world!
Hello world!
Hello world!
Hello world!
Hello world!
abc
123
5hr
[root@localhost ~]# grep abc hello.txt 
abc

2. grep也可以根据正则表达式查找字符串

其中正则表达式^[0-9]*$表示匹配数字。

[root@localhost ~]# grep ^[0-9]*$ hello.txt 
123

3. 查询时忽略大小写(-i参数)

[root@localhost ~]# grep ABC hello.txt 
[root@localhost ~]# grep -i ABC hello.txt 
abc

4. 查询时显示所查询内容的行号-n参数

[root@localhost ~]# grep -i ABC -n hello.txt 
7:abc

5. grep过滤输出

grep命令也经常与其他命令通过管道连接以起到过滤输出的作用例如之前博客里所提到的过滤进程输出因为一个系统中正在运行的进程是非常多的如果想要找到你需要查看的进程仅通过肉眼扫描是非常麻烦的如下述代码所示ps -ef表示输出所有进程信息grep python表示过滤出其中含python字符串的部分将两个代码通过管道符|连接起到 将前一个命令的输出信息输入到下一个命令的作用。
其中root 10570 6979 0 19:52 pts/1 00:00:00 grep --color=auto python这一行信息表示的是grep这个命令本身的进程信息。也可以通过-v参数再过滤一次输出如ps -ef | grep java | grep -v grep

[root@localhost /]# ps -ef | grep python
root        775      1  0 11:01 ?        00:00:00 /usr/bin/python -Es /usr/sbin/firewalld --nofork --nopid
root        804      1  0 11:01 ?        00:00:02 /usr/bin/python -Es /usr/sbin/tuned -l -P
root      10570   6979  0 19:52 pts/1    00:00:00 grep --color=auto python

最后我贴一下grep命令的帮助文档

我上面举例的都是常用的参数和基本用法如果需要更多用法请浏览下面的帮助文档例如-H可以在输出时也显示查询文档的名称。

[root@localhost ~]# grep --help
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             print version information and exit
      --help                display this help and exit
      --mmap                deprecated no-op; evokes a warning

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/>