05-02-2014
Quote:
Originally Posted by
alister
That code is vulnerable to pattern matching metacharacters. For this approach to work with arbitrary text, it is necessary to double-quote the nested parameter expansion.
You are right and your example is legitimate. I left that part out purposefully to avoid complicating matters. I should have probably mentioned it.
Quote:
Originally Posted by
alister
A minor nit: You refer to shell pattern matching as regular expressions. I'm sure you know that those are two distinct grammars, but a novice may become confused.
Yes - and no. "regular expressions" is (in a very theoretical sense) any type-3 language in the Chomsky hierarchy: a device where some characters and some metacharacters describe a text pattern. This is the case for shell regexps (aka "file globs") as well as for "Unix Basic Regular Expressions" (what awk, grep and sed use) or "Extended Regular Expressions" (i.e. perl and some GNU variants of grep, sed, ...). These are all different flavours of Regexps (and i should have mentioned that too, probably), but still Regexps nevertheless.
You are right, though, that in UNIX environments, the term "regexp" particularily describes BREs as used in sed, awk and grep. Every other use of the term, even if technically correct, might be confusing.
bakunin
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GREP(1) General Commands Manual GREP(1)
NAME
grep - search a file for lines containing a given pattern
SYNOPSIS
grep [-elnsv] pattern [file] ...
OPTIONS
-e -e pattern is the same as pattern
-c Print a count of lines matched
-i Ignore case
-l Print file names, no lines
-n Print line numbers
-s Status only, no printed output
-v Select lines that do not match
EXAMPLES
grep mouse file # Find lines in file containing mouse
grep [0-9] file # Print lines containing a digit
DESCRIPTION
Grep searches one or more files (by default, stdin) and selects out all the lines that match the pattern. All the regular expressions
accepted by ed and mined are allowed. In addition, + can be used instead of * to mean 1 or more occurrences, ? can be used to mean 0 or 1
occurrences, and | can be used between two regular expressions to mean either one of them. Parentheses can be used for grouping. If a
match is found, exit status 0 is returned. If no match is found, exit status 1 is returned. If an error is detected, exit status 2 is
returned.
SEE ALSO
cgrep(1), fgrep(1), sed(1), awk(9).
GREP(1)