在Linux中使用regex和grep在文件中查找字符串

Question

I am trying to find the proper regexes to use with the grep command on the file text.txt .

Question

1. Find all occurrences of words in text that have a substring ad, bd, cd, dd, ed.

2. Find all occurrences of numbers > 100

3. Find all occurrences of numbers > 100 that contain a digit 0 or 5

My Approach

1. grep -io '[ae]*d' text

   Prints words with the proper substrings, but doesn't print the whole string/word.

    ad d d ed d d ed d d d d ed d d 

2. grep -io '[199][1-9]*' text

   I believe I am way off on the regex, but it still prints the correct result.

    1973 197 17775 

3. grep -io '[05][1-9]*' text

   This is the continuation of 2., so I don't understand the 2. part in 3., but I believe I have the string containing a digit 0 or 5 correct.

    0 0 0 5 

Answer 1

For part (a), the -o option to grep causes it to print only the part of the line that matches the pattern, but your pattern does not match whole words. You simply need to adjust your pattern to match the parts of each word before and after the [ae]d substring.

For part (b), your pattern is all wrong. It will not match the numbers 299 or 1000, for instance. The digit pattern you want is a digit between 1 and 9 followed by at least two digits between 0 and 9 .

Part (c) is the trickiest. You must match digit patterns containing at least three digits, the first being between 1 and 9 , with either a 5 in the first position or a 0 or 5 in any other position. You probably need to separate that into alternatives with the | operator. It looks like you probably need three: the case where the lead digit is 5 ; the case where the second digit is either 0 or 5 , and the case where some later digit is 0 or 5 . In the third case you mustn't forget that there may be any number of additional digits, including zero, on either side of the 0 or 5 you match.

Answer 2

A) Find all occurrences of words in text that have a substring ad, bd, cd, dd, ed.

grep -ow '.*\(a\|b\|c\|d\|e\)d.*' text

or

egrep -ow '.*(a|b|c|d|e)d.*' text

B) Find all occurrences of numbers > 100

grep -ow '[1-9][0-9][0-9]\+' text

C) Find all occurrences of numbers > 100 that contain a digit 0 or 5

grep -ow '[1-9][0-9][0-9]\+' text | grep '\(0\|5\)'

or

grep -ow '[1-9][0-9][0-9]\+' text | egrep '(0|5)'

I'm using the option -o to output every match on it's own line and not the whole line where the pattern was found and the option -w that specifies that before and after the match should be a word boundary.