How to use grep command to find file contents in Linux

In Linux, you can use the "grep find content file" command to simply find the file content; if you want to ignore case, you can use the "grep -i find content file" command; if you want to search the directory For all files, and the line number is displayed in the result, you can use the "grep -nr find content*" command.

#The operating environment of this tutorial: Red Hat Enterprise Linux 6.1 system, Dell G3 computer.

Linux search for file contents (grep)

grep is a command commonly used on the Linux command line to find and filter the contents of text files. The simplest usage is:

grep 查找内容 文件

If you want to ignore case, you can use the -i parameter:

grep -i 查找内容 文件

If you want to search all files in the directory, including subdirectories, and display them in the results For the line number, you can use the following command:

grep -nr 查找内容 *

The syntax of grep supports regular expressions. Regular expressions are a bit complicated and will be explained later. The following are some useful parameters:

• -A num, --after-context=num: Also output the num lines after the matching line in the result

• -B num, --before-context=num: Output the num lines before the matching line in the result at the same time. Sometimes we need to display several lines of context.

• -i, --ignore-case: Ignore case

• -n, --line-number: Display line number

• -R, -r, --recursive: Search subdirectories recursively

• -v, --invert-match: Output no matching lines

We can make grep more powerful through pipeline operation. Pipeline operation is to use the output of the previous command as the input of the next command, thereby combining many simple commands to complete Complex functionality. For example, if we want to find lines containing apple, but want to filter out pineapple, we can use the following command:

grep apple fruitlist.txt | grep -v pineapple

If we want to save the search results, we can redirect the standard output of the command to File:

grep apple fruitlist.txt | grep -v pineapple > apples.txt

The difference between the redirection symbol> and the pipe operation symbol| is that the redirection is followed by a file, and no more files or commands can be followed after it; while the pipe operation is followed by Orders can be continued indefinitely. If you want to append to a file, use >>. Pipeline operation is a philosophy of the Linux command line. It is one of the few technologies in computer technology that has been used for decades. Through pipeline operations, one line of commands can complete text processing functions that thousands of lines of programs under Windows cannot.

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