On Tue, 3 Sep 2002, ANIDIL RAJENDRAN wrote:
> Newbie again.
> Sorry if this question sounds so silly
>
> Want to open filenames like ~username/blah but open doesn't interpret the tilde to
>mean the
> home directory
>
> Solution
>
> expand the filename manually with substitution
>
> $filename =~ s{ ^ ~ ( [^/]* ) }
> { $1
> ? (getpwnam($1)) [7]
> : ( $ENV{HOME} || $ENV{LOGDIR}
> || (getpwuid($>)) [7]
> )
> }ex;
>
> The auther says the following can me matched
> ~user
> ~user/blah
> ~
> ~/blah
>
> Could someone make me clear how these can be matched by the pattern inside the
>parenthesis
> which is ( [^/]*)
>
First up the two modifiers 'e' and 'x' used at the end. (perldoc perlre)
The e modifier specifies that the replacement part of the substitution is
to evaluated as perl statements and the result used for the substitution.
The x modifier tells the regex engine to ignore whitespaces and the '#'
character. This allows you to write a readable pattern match with
comments.
The search part of the substitution
{ ^ ~ ( [^/]* ) }
Note with /x modifier on, the white spaces will be ignored.
This says look for '~' at the start of $filename followed 0 or more non
'/' characters which will be saved in $1.
The replacement part
{ $1
? (getpwnam($1)) [7]
: ( $ENV{HOME} || $ENV{LOGDIR}
|| (getpwuid($>)) [7]
)
}ex;
Read through these docs, (perldoc -f getpwnam) and (perldoc -f getpwuid).
This uses the ternary operator, if $1 is true the statements after '? and
before ':' will be evaluated. If it is false that after ':' will be
evaluated. (perldoc perlop)
When $filename is '~' $1 contains nothing i.e. evaluates to false.
This means '~' is substituted by the result of the statements after ':'.
When $filename is '~user' $1 contains 'user', this means '~user' is
substituted by the results of (getpwnam($1))[7].
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