$？中的命令行perl错误值不正确？

Question

I am using command-line perl to perform a inplace substitution in a file. This is the code: (note the root perm with sudo)

sudo perl -i -pe "s/foo/bar/" config.txt

If this succeeds, 'echo $?' return 0. Now I make the file un-writable even for root using chattr like this:

sudo chattr +i config.txt

I run the same perl command and it fails with this error:

Can't remove config.txt: Operation not permitted, skipping file.

Which is fine. However, 'echo $?' still returns 0 in this case. Why is this so? Shouldn't it return a non-zero value indicating an error?

Answer 1

The problem is that Perl does not come back with a non-zero exit status for this condition ( sudo passes on the exit status of the command it was given), which is a bit vexing. You can work around the problem by recognizing that the line-reading loop is never entered if the file fails to be renamed and handle it with a flag:

sudo perl -i -ne 's/foo/bar/; print; $wrk = 1; }{ $wrk or exit 1' config.txt

The Eskimo greeting (or butterfly) "operator" }{ introduces an END block, in a way; what comes after it is executed when the loop reading lines from the file has ended. The way it works is described here .

The caveat is that this will also report an error if config.txt is empty. A shorter if a bit hackier way is to use the special $. line counter variable for the same purpose:

sudo perl -i -ne 's/foo/bar/; print; }{ $. or exit 1' config.txt