grep正则表达式

grep the regex.txt
grep "the " regex.txt
grep "^the" regex.txt
grep "^.$ " regex.txt
grep "^[0123456789]$" regex.txt
grep "^[0-9]$" regex.txt
grep "^[A-Za-z_]$" regex.txt
grep "^T[a-z][aeiou] " regex.txt
grep "^T[a-z][^aeiou] " regex.txt
grep "\[" regex.txt
grep "^[0-9-]$" regex.txt

grep "^[0-9]*" regex.txt  - match all lines
grep "^[0-9][0-9]*" regex.txt

grep "[a-z]\{4,8\}" regex.txt
grep "[a-z]\{4,\}" regex.txt
grep "[a-z]\{4\}" regex.txt
grep "[a-z]\{4\} " regex.txt
grep " [a-z]\{4\} " regex.txt


egrep "[a-z]\{4,8\}" regex.txt
egrep "^(Too|Tag)" regex.txt
egrep "(^| )the([^a-z]|$)" regex.txt
egrep "a[n]? (simple|easy)? problem" regex.txt

单引号的转义
grep -v \''\{2\}' regex.txt -- 显示0到1次单引号
grep \''\{2\}' regex.txt --显示至少2次单引号