How do I evaluate shell variables in a string?

In my Perl script I get strings of file paths that may contain environment variables, e.g. $FONTS/test.ttf or $TMP/file.txt.

I now want to open those files like this:

open my $hand开发者_运维问答le, "<$filename" or die $!;

How can I now expand the environment variables prior to the open call, as e.g. the bash shell would do?

---

If the environmental variables are set, you can use a simple substitution:

$filename =~ s/\$(\w+)/$ENV{$1}/g;

---

Why not just do this:

$filename =~ s/\$\{(\w+)\}/$ENV{$1}/g;
$filename =~ s/\$(\w+)/$ENV{$1}/g;

---

Well the following is considerably more verbose, but it seems to correctly handle both $FOO and ${FOO} syntax.

#!/usr/bin/env perl

use warnings;
use strict;

my $filename = $ARGV[0];
print(" GIVEN: <$filename>\n");
my $expanded = '';
my @parts = split(/(\$\w+)|(\${\w+})/, $filename);
foreach my $seg (@parts)
  {
    next if (not defined($seg));
    $seg = ($ENV{$1} || '')  if ($seg =~ m/\${?(\w+)}?/);
    $expanded .= $seg;
  }

print("IS NOW: <$expanded>\n");
print(`echo "  ECHO: <$filename>"`);  # How the shell did it.

Here's a sample run...

$ ./expand '$TERM ---${TERM}--- ===${FOO}=== $FOO'
 GIVEN: <$TERM ---${TERM}--- ===${FOO}=== $FOO>
IS NOW: <xterm-color ---xterm-color--- ====== >
  ECHO: <xterm-color ---xterm-color--- ====== >
$

In this version, undefined symbols are replace with an empty string, like the shell. But in my apps I'd rather leave the unexpanded invalid symbol in place making it easier to see what went wrong. Also, if you screw up your bracket matching, the shell will give you a "bad substitution" error, but here we'll just return the string with the broken symbol still in place.

---

sorry but you are wrong.

to work in perl with SHELL variables, the correct syntax is : $ENV{variable}

example with a colored GCC output function :

n=$(tput setaf 0)
r=$(tput setaf 1)
g=$(tput setaf 2)
y=$(tput setaf 3)
b=$(tput setaf 4)
m=$(tput setaf 5)
c=$(tput setaf 6)
w=$(tput setaf 7)
N=$(tput setaf 8)
R=$(tput setaf 9)
G=$(tput setaf 10)
Y=$(tput setaf 11)
B=$(tput setaf 12)
M=$(tput setaf 13)
C=$(tput setaf 14)
W=$(tput setaf 15)
END=$(tput sgr0)

colorgcc()
    {
    perl -wln -M'Term::ANSIColor' -e '
    m/not found$/ and print "$ENV{N}$`$ENV{END}", "$&", "$ENV{END}"
    or
    m/found$/ and print "$ENV{N}$`${g}", "$&", "$ENV{END}"
    or
    m/yes$/ and print "$ENV{N}$`${g}", "$&", "$ENV{END}"
    or
    m/no$/ and print "$ENV{N}$`$ENV{END}", "$&", "$ENV{END}"
    or
    m/undefined reference to/i and print "$ENV{r}", "$_", "$ENV{END}"
    or
    m/ Error |error:/i and print "$ENV{r}", "$_", "$ENV{END}"
    or
    m/ Warning |warning:/i and print "$ENV{y}", "$_", "$ENV{END}"
    or
    m/nsinstall / and print "$ENV{c}", "$_", "$ENV{END}"
    or
    m/Linking |\.a\b/ and print "$ENV{C}", "$_", "$ENV{END}"
    or
    m/Building|gcc|g\+\+|\bCC\b|\bcc\b/ and print "$ENV{N}", "$_", "$ENV{END}"
    or
    print; '
    }