1.1.1.txt
 1.1.txt
 1.txt
 2.txt
 3.txt

##</code><code>##

perl -e "print grep {/\d+\.txt/} glob('*.txt');"
1.1.1.txt1.1.txt1.txt2.txt3.txt

##</code><code>##

perl -e "$s=qq(1.1.1); if ($s=~/\d+/) {print 'it is a number'};"
it is a number

##</code><code>##

perl -e "$s=qq(1.1.1); if ($s=~/\d+?/) {print 'it is a number'};"
it is a number