Shebang行与Perl的最大长度？

Question

I've read somewhere that in Linux a shebang line ( #! ) can't exceed 127 characters. I have a Perl script which has a shebang line of over 300 characters, and it hasn't failed (yet). Does the limit apply only to the executable path (which is under 100 chars in my case), or is there some strange magic at work?

Answer 1

Does the limit apply only to the executable path (which is under 100 chars in my case), or is there some strange magic at work?

The limit applies only to the executable path because there is strange magic at work. The strange magic goes by the name of Perl.

First, the limit of 127 characters is true. (Or maybe 128 or 126, didn't actually count.) Everything past that gets truncated. Second, regardless of whether there are spaces on the shebang line Linux will pass everything after the executable name as just ONE argument. Third, Perl will parse the shebang line and interpret it itself, which is why this was working. But note that the effect of all this is strange and a bit perverse. Suppose the shebang line looked like this:

#!/bin/perl -I/lib-one -I/lib-two

And suppose the truncation happened near the end, say, right before the "w" in "two" (that is, suppose the limit were 32 instead of 128, for ease of reading). Then the effect is as if you invoked perl at the command line as follows:

shell-prompt$ /bin/perl "-I/lib-one -I/lib-t" -I/lib-one -I/lib-two

Which "works" in this case, but in general won't.

Answer 2

I know this doesn't answer your original question about the maximum #! line but I guess you rather have an XY problem .

Why don't you use lib ? If you have hard coded include paths in your script (in your shebang line) anyway then you can as well denote them with use lib statements and keep the shebang line short:

#!/usr/bin/perl -some -absolutely -necessary -options

use lib '/lib-one';
use lib '/lib-two';
...
use lib '/lib-twenty-four';