2012/12/9 Cheer Xiao <xiaqq...@gmail.com>: > Hi all, > > For those not acquainted with zsh: extended globbing is one of the > many features of zsh that allows you to match files satisfying a given > criteria in a inline manner (instead of going through a loop). For > example, "echo abc*(/)" gives you all directories with names starting > with "abc" in current directory, while "rm .*(@)" removes all symlinks > with names starting with ".", etc. It is a useful feature, but I don't > really like the arcane syntax. > > Fish doesn't have extended globbing (which is good actually :-), so > I'm tempted to write this: > > function filter > set predicate $argv[1] > for i in (seq 2 (count $argv)) > test $predicate $argv[$i]; and echo $argv[$i] > end > end > > So now I write "echo (filter -d abc*)" and "rm (filter -L .*)" to > achieve the same effect as "echo abc*(/)" and "rm .*(@)" in zsh. It is > more verbose, but the readability is considerably better; it also > allows you to reuse the knowledge of the "test" builtin. > > This works fine until, of course, you start to encounter file names > containing newlines. Try this: > > cd (mktemp -d) > mkdir 'a > b' > count * > count (filter -d *) > > Clearly, The problem stems from the fact that when fish expands the > command substitution (filter -d *), filenames echo'ed by "filter" run > together before being split on newlines to render the substituted > words. A newline in one of the filenames is then indistinguishable > with two filenames. > > So this leads to my proposal: > > * When evaluating a fish function, maintain an alternative output > buffer besides stdout. The buffer is actually a dynamic-sized list > (std::vector for C++ programmers) of strings. Introduce a new builtin > (say "put") to write to that buffer. > > * Exactly one of the two output buffers (let's call them stdout and > altout) should be active within a function. > > * Within functions, calling "put" activates the altout and closes > stdout. Each invocation of "put" with k arguments appends k new > elements to altout. (The relationship between altout and stdout still > needs some thoughts though.) > > * When command substitution is performed, it is checked which of > stdout and altout is active (the latter is only possible for fish > functions; external commands always have only stdout active). If > altout is active, the elements in altout are substituted directly. If > stdout is active, the content in stdout is split on newlines before > being substituted (as is currently done). > > * When altout is written to when there is no enclosing command > substitution (eg. calling "put" on the prompt), anything written to it > is directed to stdout plus a newline. > > With altout I can write my "filter" by replacing "echo" with "put" and > it's now newline-safe. > > Being able to output arrays of strings can be of many other uses - > actually it enables you to write any array manipulating functions in > an easy way. > > If the newline-in-filenames stuff sounds too invented and unlikely, > consider why shells need real arrays instead of strings joined by > delimiters (be it whitespace or newlines) at all. Actually, one of the > favorite things about fish is its clean array syntax, it is a really > nice thing. I think fish deserves the added expressive power. :)
Oops. Digging into the source, it turns out fish has no true array; instead array are strings joined with "\x1e". This should be resolved first. I've opened an issue for that: https://github.com/fish-shell/fish-shell/issues/436 -- Regards, Cheer Xiao ------------------------------------------------------------------------------ LogMeIn Rescue: Anywhere, Anytime Remote support for IT. Free Trial Remotely access PCs and mobile devices and provide instant support Improve your efficiency, and focus on delivering more value-add services Discover what IT Professionals Know. Rescue delivers http://p.sf.net/sfu/logmein_12329d2d _______________________________________________ Fish-users mailing list Fish-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/fish-users
