Peng Yu wrote:
> I know that I should use =~ to match regex (bash version 4).
>
> However, the man page is not very clear. I don't find how to match
> (matching any single character). For example, the following regex
> doesn't match xxxxtxt. Does anybody know how to match any character
> (should be '.' in perl) in bash.
>
> [[ "$1" =~ "xxx.txt" ]]
The manual page for bash says that the rules of regex(3) apply:
An additional binary operator, =~, is available, with the
same
precedence as == and !=. When it is used, the string to the
right
of the operator is considered an extended regular expression
and
matched accordingly (as in regex(3)). The return value is 0 if
the
string matches the pattern, and 1 otherwise.
and also:
Any part of the pattern may be quoted to force it to be matched
as a
string.
Thus in the expression [[ "$1" =~ "xxx.txt" ]] the fact that the pattern
is quoted [here the whole pattern appears within double quotes] has turned the
dot '.' into a plain literal character, instead of a meta-character which
matches
any single character.
The usual method of avoiding quotes in the pattern is to omit them:
[[ $1 =~ xxx.txt ]] # the dot '.' in the pattern is a
meta-character
or to use a variable:
pattern="xxx.txt" # a 7-character string
[[ $1 =~ $pattern ]] # the dot '.' in $pattern is a
meta-character
Example: using all literals in an instance of bash:
$ [[ xxxxtxt =~ xxx.txt ]] && echo true
true
$
Also notice that quotes are not needed around the left-hand side $1 :
Word
split‐
ting and pathname expansion are not performed on the words
between
the [[ and ]] ...
Thus there is no need to use quotation marks to suppress word splitting
inside double brackets [[ ... ]].
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