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Apply environment expansion to options in .stowrc files

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Expand environment variables used in stowrc, as requested in

    https://savannah.gnu.org/bugs/?41826

This is achieved by creating a new function expand_environment() that
replaces any substring of the form '$VAR' or '${VAR}' with contents of
environment variable $VAR.  Literal '$' can be given by '\$'.

N.B. The function is only applied to the --target and --dir options,
and only for options specified in .stowrc; cli options are left
untouched.

Undefined variables are expanded to the empty string, as they would be
in normal shell parameter expansion.

Unit tests added accordingly:

  - Test expand_environment():
    * Expand $HOME
    * Expand ${HOME}
    * Expand ${WITH SPACE}
    * Expand '\$HOME'. Expected is '$HOME'
    * Expand ${UNDEFINED}. Expected is ''.

  - Test that it's applied to the correct options.

  - Test that CLI options are not expanded.
This commit is contained in:
Charles LeDoux 2016-07-14 11:37:42 -05:00 • committed by Adam Spiers
parent 4d1167ffd7
commit 9674738792
3 changed files with 123 additions and 4 deletions
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54
bin/stow.in
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@ -632,7 +632,8 @@ sub check_packages {
# Returns : (\%rc_options, \@rc_pkgs_to_unstow, \@rc_pkgs_to_stow)
# Throws : a fatal error if a bad option is given
# Comments : Parses the contents of '~/.stowrc' and '.stowrc' with the same
# parser as the command line options.
# parser as the command line options. Additionally expands any
# environment variables in --target or --dir options.
#=============================================================================
sub get_config_file_options {
my @defaults = ();
@ -647,7 +648,56 @@ sub get_config_file_options {
close $FILE or die "Could not close open file: $file\n";
}
}
return parse_options(@defaults);
# Parse the options
my ($rc_options, $rc_pkgs_to_unstow, $rc_pkgs_to_stow) = parse_options(@defaults);
# Expand environment variables and glob characters.
if (exists $rc_options->{target}) {
$rc_options->{target} =
expand_environment($rc_options->{target}, '--target option');
}
if (exists $rc_options->{dir}) {
$rc_options->{dir} =
expand_environment($rc_options->{dir}, '--dir option');
}
return ($rc_options, $rc_pkgs_to_unstow, $rc_pkgs_to_stow);
}
#===== SUBROUTINE ============================================================
# Name : expand_environment()
# Purpose : Expands evironment variables.
# Parameters: $path => string to perform expansion on.
# : $source => where the string came from
# Returns : String with replacements performed.
# Throws : n/a
# Comments : Variable replacement mostly based on SO answer
# : http://stackoverflow.com/a/24675093/558820
#=============================================================================
sub expand_environment {
my ($path, $source) = @_;
# Replace non-escaped $VAR and ${VAR} with $ENV{VAR}
# If $ENV{VAR} does not exist, perl will raise a warning
# and then happily treat it as an empty string.
$path =~ s/(?<!\\)\$\{((?:\w|\s)+)\}/
_safe_expand_env_var($1, $source)
/ge;
$path =~ s/(?<!\\)\$(\w+)/
_safe_expand_env_var($1, $source)
/ge;
# Remove \$ escapes.
$path =~ s/\\\$/\$/g;
return $path;
}
sub _safe_expand_env_var {
my ($var, $source) = @_;
unless (exists $ENV{$var}) {
die "$source references undefined environment variable \$$var; " .
"aborting!\n";
}
return $ENV{$var};
}
#===== SUBROUTINE ===========================================================