$str = "abcdefghij";
$str = strtr($str, "abcdef", "XYZ");

results in "XYZdefghij"

where as in standard unix:

echo "abcdefghij" | tr 'abcdef' 'XYZ'

would output "XYZZZZghij" because the last character
is repeated automatically. Some versions will return
"XYZXYZghij" because they reuse the second string, but
I'm not if that's the "correct" behaviour, or if the
fisrt one is... for what I'm trying to accomplish it
doesn't matter though.

An example of why this is a problem...

$obj_nom = "The Foo-Object";
$file_nom = strtr($obj_nom, " -", ""); // or ..., '');

One would expect this to assign "TheFooObject" to
$file_nom... but instead no translation is performed.

This would also be the same as:

tr -d ' -'

which is logically equivalent to:

tr ' -' ''

There does not appear to be a native php function to
do the same thing, infact the editors of the user coments
have a couple times told people to use strtr or one of
the regexp replacement libraries to accomplish this...
not knowing that none of them seem to do so.