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Split View: Linux grep 명령어 기초

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Linux grep 명령어 기초

Overview

Linux 에는 grep 이라는 유용한 도구가 있습니다. 이 도구를 잘 활용하면, 텍스트 파일에서 유용한 정보를 추출할 수 있습니다.

grep document

grep
$ grep -h
usage: grep [-abcdDEFGHhIiJLlMmnOopqRSsUVvwXxZz] [-A num] [-B num] [-C[num]]
	[-e pattern] [-f file] [--binary-files=value] [--color=when]
	[--context[=num]] [--directories=action] [--label] [--line-buffered]
	[--null] [pattern] [file ...]

options

  • -A num --after-context : 찾은 line 기준으로 그 다음 num 개의 line을 더 화면에 표시
  • -B num --before-context : 찾은 line 기준으로 그 이전 num 개의 line을 더 화면에 표시
  • -C num --context: 찾은 line 기준으로 앞, 뒤 num개의 line을 화면에 표시
  • -c --count : 찾은 결과의 line 수
  • -E pattern --regexp=pattern: 정규표현식 pattern에 일치하는 line 출력
  • -f file --file=file : file로 부터 pattern 읽기
  • -r --recursive: 하위 디랙터리를 재귀적으로 탐색
  • -n --line-number: 라인 number를 표시
  • -v pattern : 해당 패턴에 matching되는 line을 제외하고 출력

examples

아래와 같은 test.txt 파일이 있다고 가정하겠습니다.

test.txt
$ cat test.txt

apple is sweety
banana is long
apple mango
pitch is
water melon is expensive
grapes are cheep
pear

grep pattern -A num text

$ grep apple -A 2 test.txt
apple is sweety
banana is long
apple mango
pitch is
water melon is expensive

grep pattern -B num text

$ grep apple -B 1 test.txt
apple is sweety
banana is long
apple mango

grep pattern -C num text

$ grep apple -C 1 test.txt
apple is sweety
banana is long
apple mango
pitch is

grep pattern -c text

grep apple -c  test.txt
2

grep -e pattern text

$ grep -e "ap" test.txt
apple is sweety
apple mango
grapes are cheep

grep -f file text

$ cat regex.txt
apple

$ grep -f regex.txt test.txt
apple is sweety
apple mango

grep -n pattern text

$ grep -n appl test.txt
1:apple is sweety
3:apple mango

grep -v pattern word

appl 을 제외한 줄을 출력.

$ grep -v appl test.txt
banana is long
pitch is
water melon is expensive
grapes are cheep
pear

다른 명령어와 조합

with > (redirection)

grep 결과를 out에 저장

$ grep -v appl test.txt > out.txt
$ cat out.txt
banana is long
pitch is
water melon is expensive
grapes are cheep
pear

with awk

첫 번째 단어만 출력

$ grep -v appl test.txt | awk '{print $1}'
banana
pitch
water
grapes
pear

with sort, uniq

첫번 째 단어를 정렬하고 중복 제거

$ grep ap test.txt | awk '{print $1}' | sort | uniq
apple
grapes

regex에 대해서 더 공부하고 싶거나 test 하고 싶다면, regexr.com에서 공부.

regexr-example

Linux grep Command Basics

Overview

Linux has a useful tool called grep. By making good use of this tool, you can extract useful information from text files.

grep document

grep
$ grep -h
usage: grep [-abcdDEFGHhIiJLlMmnOopqRSsUVvwXxZz] [-A num] [-B num] [-C[num]]
	[-e pattern] [-f file] [--binary-files=value] [--color=when]
	[--context[=num]] [--directories=action] [--label] [--line-buffered]
	[--null] [pattern] [file ...]

options

  • -A num --after-context: Display num additional lines after the matched line
  • -B num --before-context: Display num additional lines before the matched line
  • -C num --context: Display num lines before and after the matched line
  • -c --count: Count the number of matched lines
  • -E pattern --regexp=pattern: Output lines matching the regular expression pattern
  • -f file --file=file: Read pattern from file
  • -r --recursive: Recursively search subdirectories
  • -n --line-number: Display line numbers
  • -v pattern: Output all lines except those matching the pattern

examples

Let's assume we have a test.txt file with the following content.

test.txt
$ cat test.txt

apple is sweety
banana is long
apple mango
pitch is
water melon is expensive
grapes are cheep
pear

grep pattern -A num text

$ grep apple -A 2 test.txt
apple is sweety
banana is long
apple mango
pitch is
water melon is expensive

grep pattern -B num text

$ grep apple -B 1 test.txt
apple is sweety
banana is long
apple mango

grep pattern -C num text

$ grep apple -C 1 test.txt
apple is sweety
banana is long
apple mango
pitch is

grep pattern -c text

grep apple -c  test.txt
2

grep -e pattern text

$ grep -e "ap" test.txt
apple is sweety
apple mango
grapes are cheep

grep -f file text

$ cat regex.txt
apple

$ grep -f regex.txt test.txt
apple is sweety
apple mango

grep -n pattern text

$ grep -n appl test.txt
1:apple is sweety
3:apple mango

grep -v pattern word

Output lines excluding those containing "appl".

$ grep -v appl test.txt
banana is long
pitch is
water melon is expensive
grapes are cheep
pear

Combining with other commands

with greater-than (redirection)

Save grep results to out

$ grep -v appl test.txt > out.txt
$ cat out.txt
banana is long
pitch is
water melon is expensive
grapes are cheep
pear

with awk

Print only the first word

$ grep -v appl test.txt | awk '{print $1}'
banana
pitch
water
grapes
pear

with sort, uniq

Sort the first word and remove duplicates

$ grep ap test.txt | awk '{print $1}' | sort | uniq
apple
grapes

If you want to study or test regex further, check out regexr.com.

regexr-example

Quiz

Q1: What is the main topic covered in "Linux grep Command Basics"? Learn the basics of grep, a useful text search command-line tool in Linux.

Q2: What is options? -A num --after-context: Display num additional lines after the matched line -B num --before-context: Display num additional lines before the matched line -C num --context: Display num lines before and after the matched line -c --count: Count the number of matched lines -E pattern...

Q3: Explain the core concept of grep -v pattern word. Output lines excluding those containing "appl". Combining with other commands

Q4: What are the key aspects of with greater-than (redirection)? Save grep results to out

Q5: How does with awk work? Print only the first word