如何使用 awk 打印匹配的正则表达式模式？

Question

Using awk , I need to find a word in a file that matches a regex pattern.

I only want to print the word matched with the pattern.

So if in the line, I have:

xxx yyy zzz

And pattern:

/yyy/

I want to only get:

yyy

---

EDIT: thanks to kurumi i managed to write something like this:

awk '{
        for(i=1; i<=NF; i++) {
                tmp=match($i, /[0-9]..?.?[^A-Za-z0-9]/)
                if(tmp) {
                        print $i
                }
        }
}' $1

and this is what i needed :) thanks a lot!

Answer 1

This is the very basic

awk '/pattern/{ print $0 }' file

ask awk to search for pattern using // , then print out the line, which by default is called a record, denoted by $0. At least read up the documentation .

If you only want to get print out the matched word.

awk '{for(i=1;i<=NF;i++){ if($i=="yyy"){print $i} } }' file

Answer 2

It sounds like you are trying to emulate GNU's grep -o behaviour. This will do that providing you only want the first match on each line:

awk 'match($0, /regex/) {
    print substr($0, RSTART, RLENGTH)
}
' file

Here's an example, using GNU's awk implementation ( gawk ):

awk 'match($0, /a.t/) {
    print substr($0, RSTART, RLENGTH)
}
' /usr/share/dict/words | head
act
act
act
act
aft
ant
apt
art
art
art

Read about match , substr , RSTART and RLENGTH in the awk manual.

After that you may wish to extend this to deal with multiple matches on the same line.

Answer 3

gawk can get the matching part of every line using this as action:

{ if (match($0,/your regexp/,m)) print m[0] }

match(string, regexp [, array]) If array is present, it is cleared, and then the zeroth element of array is set to the entire portion of string matched by regexp. If regexp contains parentheses, the integer-indexed elements of array are set to contain the portion of string matching the corresponding parenthesized subexpression. http://www.gnu.org/software/gawk/manual/gawk.html#String-Functions

Answer 4

If you are only interested in the last line of input and you expect to find only one match (for example a part of the summary line of a shell command), you can also try this very compact code, adopted from How to print regexp matches using `awk`? :

$ echo "xxx yyy zzz" | awk '{match($0,"yyy",a)}END{print a[0]}'
yyy

Or the more complex version with a partial result:

$ echo "xxx=a yyy=b zzz=c" | awk '{match($0,"yyy=([^ ]+)",a)}END{print a[1]}'
b

Warning: the awk match() function with three arguments only exists in gawk , not in mawk

Here is another nice solution using a lookbehind regex in grep instead of awk . This solution has lower requirements to your installation:

$ echo "xxx=a yyy=b zzz=c" | grep -Po '(?<=yyy=)[^ ]+'
b

Answer 5

If Perl is an option, you can try this:

perl -lne 'print $1 if /(regex)/' file

To implement case-insensitive matching, add the i modifier

perl -lne 'print $1 if /(regex)/i' file

To print everything AFTER the match:

perl -lne 'if ($found){print} else{if (/regex(.*)/){print $1; $found++}}' textfile

To print the match and everything after the match:

perl -lne 'if ($found){print} else{if (/(regex.*)/){print $1; $found++}}' textfile

Answer 6

题外话，这也可以使用 grep 来完成，如果有人正在寻找 grep 解决方案，只需将其张贴在这里

echo 'xxx yyy zzze ' | grep -oE 'yyy'

Answer 7

Using sed can also be elegant in this situation. Example (replace line with matched group "yyy" from line):

$ cat testfile
xxx yyy zzz
yyy xxx zzz
$ cat testfile | sed -r 's#^.*(yyy).*$#\1#g'
yyy
yyy

Relevant manual page: https://www.gnu.org/software/sed/manual/sed.html#Back_002dreferences-and-Subexpressions

Answer 8

If you know what column the text/pattern you're looking for (eg "yyy") is in, you can just check that specific column to see if it matches, and print it.

For example, given a file with the following contents, (called asdf.txt )

xxx yyy zzz

to only print the second column if it matches the pattern "yyy", you could do something like this:

awk '$2 ~ /yyy/ {print $2}' asdf.txt

Note that this will also match basically any line where the second column has a "yyy" in it, like these:

xxx yyyz zzz
xxx zyyyz