#bin/bash
STR="1234567890asdfghjkl"
echo "first character ${STR:0:1}"
echo "The three characters ${STR:0:3}"
echo "第四个字符开始显示:${STR:3}"
echo "显示第4到6个字符:${STR:3:3}"
echo "显示最后1个字符:${STR:0-1}"
echo "显示最后3个字符:${STR:0-3}"
echo "从右边数第7个，取3个字符${STR:0-7:3}"
总结：
${STR:开始位置:截取几个字符}
开始位置0-开始是从右边数如 0-7 表示从右边数第7个
STR=abc123bcd456123abc777
echo ${STR#*123} #bcd456123abc777
echo ${STR##*123} #abc777
echo ${STR%123*} #abc123bcd456
echo ${STR%%123*} #abc
