Unix Shell脚本从字符串中提取数字

Question

How to extract the bold number from the string below using unix shell script?

17: H.0(-2073):File ID (40008)in xyz file not equal to the file ID(**40004**)in file header.

Thanks :)

Answer 1

echo '17: H.0(-2073):File ID (40008)in xyz file not equal to the file ID(40004)in file header.' | sed -e 's/.*(\([0-9]*\)).*/\1/'

The second part of this line runs sed with command s (substitution). Part between first two slashes ( / ) is regular expression which matches the following:

Everything ( .* ) in greedy manner, ie until the last occurrence of any number of digits in brackets ( ([0-9]*) ) and then everything again ( .* ) until the end of line. Expression between \\( and \\) (ie 40004 in this case) is memorized to be used in the second part of s command.

The part between the second / and third / is what we want to place instead of the line matched with regular expression. Here it is \\1 , meaning reference to the substring between 1st occurrence of \\( and \\) which is 40004 in our case.

So the part after | replaces the whole input string with string 40004 extracted from it. Regular expressions are powerful but often write-only technique, so I hope this explanation will bring a bit more clarity.