How to use grep to find pattern matching across multiple lines

grep Is a command line text search utility , Be able to find patterns and strings in files and other types of input . Most matches match only one line , But matching across multiple lines is often useful .

Use grep Match multiple new lines

It is difficult to deal with multi line matching grep . A better tool is awk or sed, Both of them can naturally handle multiple lines of input . Using two expressions with commas will match everything between these two patterns .

awk '/from/,/to/' file
sed -n '/from/,/to/p' file

Still can be in To deal with this problem grep, But the command is very clumsy .

grep -Pz '(?s)from.*n.*to' test

There are several things that have been done ：

1. -P open Perl Compatible regular expressions .
2. -z Provide the entire file as a line , Use “ Zero byte ” Not line breaks . This allows grep Treat the whole thing as one line . (?s) open PCRE_DOTALL, send . Characters match any character , Include line breaks .
3. from It's the starting game .
4. .n. Will match everything , until to, This is the end match .
   Overall speaking , This will be done for scripting purposes , But if you type it yourself , Please remember a lot . Besides , Use this -o The flag prints only matching items and also trailing zero byte characters , This can lead to other problems .

Use pcre2grep Instead of （Perl Compatible grep）

just grep Is not the best tool to complete this work , There's an alternative pcre2grep , Out of the box land support Perl Compatible regular expressions , And it can easily match multi line regular expressions .

It may already be installed on your system , But if not , You can get it from the package manager ：

sudo apt install pcre2-utils

then , You only need to use -M Parameter to run it .

pcre2grep -M 'from(n|.)*to' file

Please note that , This still requires you to manually “ Newline or any character ” And (n|.)* . perhaps , You can use the (?s) Tips open PCRE_DOTALL And make the dot character match the newline character .

pcre2grep -M '(?s)from.*to' file