php正则表达式匹配第一个和最后一个

Question

i'm new to regular expressions and would like to match the first and last occurrences of a term in php. for instance in this line:

"charlie, mary,bob,bob,mary, charlie, charlie, mary,bob,bob,mary,charlie"

i would like to just access the first and last "charlie", but not the two in the middle. how would i just match on the first and last occurrence of a term?

thanks

Answer 1

If you know what substring you're looking for (ie. it's not a regex pattern), and you're just looking for the positions of your substrings, you could just simply use these:

strpos — Find position of first occurrence of a string

strrpos — Find position of last occurrence of a char in a string

Answer 2

Try this regular expression:

^(\w+),.*\1

The greedy * quantifier will take care that the string between the first word ( \\w+ ) and another occurrence of that word ( \\1 , match of the first grouping) is as large as possible.

Answer 3

You need to add ^ and $ symbols to your regular expression.

• ^ - matches start of the string
• $ - matches end of the string

In your case it will be ^charlie to match first sample and charlie$ to match last sample. Or if you want to match both then it will be ^charlie|charlie$ .

See also Start of String and End of String Anchors for more details about these symbols.

Answer 4

Try exploding the string.

$names = "charlie, mary,bob,bob,mary, charlie, charlie, mary,bob,bob,mary,charlie";
$names_array = explode(",", $names);

After doing this, you've got an array with the names. You want the last, so it will be at position 0.

$first = $names_array[0];

It gets a little trickier with the last. You have to know how many names you have [count()] and then, since the array starts counting from 0, you'll have to substract one.

$last = $names_array[count($names_array)-1];

I know it may not be the best answer possible, nor the most effective, but I think it's how you really start getting programming, by solving smaller problems.

Good luck.