One linux command a day - grep

grep (abbreviated from Globally search a Regular Expression and Print) is a powerful text search tool that searches text using specific pattern matches (including regular expressions) and outputs matching lines by default.

Syntax Usage: grep [OPTION]... PATTERNS [FILE]...

example:

This is a simple file with some simple content.

Output the content of the line where hello is located

grep 'hello' testsimplegrep.txt

Output lines with hello regardless of case

grep -i 'hello' testsimplegrep.txt

Pattern selection and interpretation (optional pattern and interpretation)

-E sums -e:

-e can only pass one parameter, if you need to pass multiple parameters, you need to -e

For example: grep -e 'HELLO' -e 'test' testssimplegrep.txt

If you use -E, multiple parameters can be separated by |

Syntax: grep -E 'HELLO|test|linux' testsimplegrep.txt | means or (or)

Use of grep -F:

View the contents of the file as follows

grep -F means to treat the grep command as using fixed strings (fixed strings) instead of regular expressions to match patterns. In this mode, grep searches for strict text matches, rather than using special characters in regular expressions. This is usually faster than regular expressions.

When using the -F option, you need to pay attention that the pattern string cannot contain metacharacters of regular expressions, such as parentheses, asterisks, etc. grep will match the pattern string as normal text.

Let's take a look at the results of using -E: grep -E 'test|rege' testsimplegrep.txt