predefined character classes in grep

Stefan — Sun, 06 Jul 2008 15:54:00 +0200

Many regex implementations have “macros” for various character classes. In Perl, for example, \d matches any digit ([0-9]) and \w matches any “word character” ([a-zA-Z0-9_]). Grep uses a slightly different notation for the same thing: [:digit:] for digits and [:alnum:] for alphanumeric characters. (BSD)

Finally, certain named classes of characters are predefined within bracket expressions, as follows. Their names are self explanatory, and they are [:alnum:], [:alpha:], [:cntrl:], [:digit:], [:graph:], [:lower:], [:print:], [:punct:], [:space:], [:upper:], and [:xdigit:]. For example, [[:alnum:]] means [0-9A-Za-z]. (grep man page)

Was unter Ruby

line = "length 1450"
puts line if line =~ /\d{4}/

heißt wird also unter der bash mit grep zu

export line="length 1450"
echo $line | egrep [[:digit:]]{4}

was zwar die regulären Ausdrücke unnötig aufbläht, aber immerhin die gleiche Funktionalität zur Verfügung stellt.

loopkid: predefined character classes in grep

predefined character classes in grep