Shell basic regular expressions and extended regular expressions

The difference between BRE and ERE

The basic difference between a regular expression (BRE) and extended regular expressions (ERE) is simply the difference between meta-characters (meta charactor) of it .

• BRE:. Only ^ $ * [] is metacharacters

• ERE:.? ^ $ [] * + () {} | Are metacharacters

BRE and ERE metacharacters

Reference: Shell Regular Expressions

Examples

$echo "abcdefg" | grep 'a.+g' #不匹配任何字符串
$echo "abcdefg" | grep 'a.\+g' #匹配整个字符串
$echo "abcdefg" | grep -E 'a.+g' #使用扩展正则表达式，匹配整个字符串