grep command

A command to search for matching lines in a regular expression

syntax

grep [option] pattern [file] ex: grep -n abc aaa.txt

★★★★★（5/5） Required. If you don't remember this, it will hinder your daily work.

-e: Use regular expressions (regex e?)
-n: Show line number in search results (number, common abbreviation)
-C5: Display the specified 5 lines before and after the part that matches the search result (the number of lines is arbitrary. Maybe C has no meaning, before, after, and before and after each match in A, B, C, so ABC which Maybe you should remember it
-r: Search in directories (recursive, common omission)
-i: Case insensitive search (case insensitive i. Maybe ...)

grep'^ A'sample.csv → A is added at the beginning of the line
grep'\ [0-9]' sample.csv → Extract the line containing the character string'[0-9]'
ps aux | grep python → Extract processes that contain the characters python
grep -v'^ A'sample.csv → A is not added at the beginning of the line
grep -e aaa -e bbb sample.csv → Extract the line containing either aaa or bbb
grep -i aaa sample.csv → Case-insensitive, extract lines containing aaa

appendix

grep aaa sample.csv | grep bbb

→ Narrow down to those that contain aaa, and further narrow down to those that contain bbb

grep -e aaa-e bbb sample.csv

→ Repeat the -e option multiple times. Extract the line containing aaa and the line containing bbb.

ls ./ | grep aaa

→ Extract files containing aaa (file name) in the current directory (current directory).

grep aaa -rl ./

→ Files in the current directory (current directory) that contain aaa

history | grep aaa | tail

→ Extract commands including aaa from history commands. Narrow down to the last 5 with tail.

The grep command is required, so it's a good idea to remember it!