Perl oneliner match repeating itself

Question

I'm trying to read a specific section of a line out of a file with Perl. The file in question is of the following syntax.

# Sets $USER1$ 
$USER1$=/usr/....
# Sets $USER2$ 
#$USER2$=/usr/...

My oneliner is simple,

perl -ne 'm/^\$USER1\$\s*=\s*(\S*?)\s*$/m; print "$1";' /my/file

For some reason I'm getting the extraction for $1 repeated several times over, apparently once for every line in the file after my match occurs. What am I missing here?

You need a conditional to test for a match, such as `print if /..your regex ../;` — , Nov 30 '11 at 22:22

score 5 · Accepted Answer · answered Nov 30 '11 at 22:15

5

You are executing print for every line of the file because print gets called for every line, whether the regex matches or not. Replace the first ; with an &&.

answered Nov 30 '11 at 22:15

Jeff Burdges

4,204
23
46

Or reset the `$1=""` after each line, but that's less elegant. – Jeff Burdges Nov 30 '11 at 22:17
Perfect, thanks. Figured it was some kind of logic condition problem. – Tim Brigham Nov 30 '11 at 22:21
@ennuikiller You absolutely CAN easily reset $1. The match variables are reset on any successful match, so match m// (the empty string) to reset them! – tadmc Dec 01 '11 at 03:14

score 2 · Answer 2 · answered Nov 30 '11 at 22:14

From perlre:

NOTE: Failed matches in Perl do not reset the match variables, which makes it easier to write code that tests for a series of more specific cases and remembers the best match.

Try this instead:

perl -ne 'print "$1" if m/^\$USER1\$\s*=\s*(\S*?)\s*$/m;' /my/file

score 1 · Answer 3 · answered Nov 30 '11 at 22:19

1

$ cat test.txt
# Sets $USER1$ 
$USER1$=/usr/....
# Sets $USER2$ 
#$USER2$=/usr/...

$ perl -nle 'print if /^\$USER1/;' test.txt
$USER1$=/usr/....

answered Nov 30 '11 at 22:19

score 0 · Answer 4 · answered Nov 30 '11 at 22:12

0

Try this

perl -ne '/^.*1?=([\w\W].*)$/;print "$1";' file

answered Nov 30 '11 at 22:12

KKDK

1

Perl oneliner match repeating itself

4 Answers4