3 ms·

Have something​ against [[ ]] ?

• dozzie 10y ago
  Of course I have. [[ ]] is shell-specific, which for scripts almost always means bash-specific, and bash has a history of subtly changing semantics of such constructs. I've seen scripts suddenly stop working for no apparent reason, only to discover later that bash upgrade changed how [[ == ]] treated unanchored patterns (or something of similar caliber). And now go figure where the bug is. Most of the time, whatever is in [[ ]] can be easily emulated with POSIX/SUS-compatible tools and most of the time it doesn't matter that the tool is not a shell built-in.
  • pyre 10y ago
    [[ ]] works in bash, zsh, and (iirc) ksh. Saying it's "bash-specific" isn't accurate.
    • dozzie 10y ago
      Depends on what you mean by "works". Yes, all three shells recognize [[ ]] construct, as it was specifically added to SUS (or POSIX?) for implementation-specific things, but how they interpret it is up to the specific shell. Let's take people's favourite =~ operator. In bash, according to documentation, it uses ERE syntax. In zsh, it is ERE or PCRE, depending on an option being set. This is a subtle but important difference in how [[ ]] works. And then again, your environment can change the behaviour of a script you're running, which is (a) unexpected and (b) undesirable, and the change in the behaviour can range from "doesn't find thing it should" to "crashes" to "goes awry in an unexpected way".