Grep basic and practice

定义：Grep (Globally search for the reqular expression and print out the line).

好处：Grep 在执行时不需要先调用编辑程序，同时不需要以“//” 来括起规则表达式，所以比vi等快很多。

格式：grep pattern filename1 filename2 .....

术语：pattern, 字符串样式，多被单引号‘ ’包围。

原理：Grep 在文件里查找规则表达式，并打印包含该表达式的所有行。

Practice script

#/bin/bash
echo 'here is a grep script'
echo '======= print the content of employees'
cat employees
#search line including eric
grep eric employees

echo '======= grep option practice'
#show line and line number
grep -n '^er' employees
#print bash return, ,,
echo $?
#print line number only
grep -c '^er' employees
#print filename only
grep -l '^er' employees awkfile
#display matching word file and line
grep -w tokoyo employees awkfile
#ignore capital
grep -i tOKoyo employees awkfile
#print unmatch line
grep -v tokoyo employees
#mark module number
grep -b tokoyo employees
#print error only
grep -s tokoyo employees

#regular expression practice
echo '======= regular expression practice'
grep frank emp*
grep '^green' employees
grep '12$' employees
grep '939..' employees
grep '^[ej]' employees
grep '^j..[nk]' employees
grep '\<mar.*' employees
grep '\<mar.*12' employees
grep -vin 'ic' employees
grep -l 'ic' employe*

Output of the script

# ./grep.sh
here is a grep script
======= print the content of employees
eric    beijing
john    xian
mark    henan
frank    tokoyo
green    england
eric    beijing
======= grep option practice
:eric    beijing       

employees
employees:frank    tokoyo
employees:frank    tokoyo
eric    beijing
john    xian
mark    henan
green    england
:frank    tokoyo
frank    tokoyo
======= regular expression practice
frank    tokoyo
green    england
mark    henan
mark    henan
eric    beijing
john    xian
john    xian
mark    henan
mark    henan
:john    xian
:mark    henan
:frank    tokoyo
:green    england
employees

q