Nicolas Williams
bd7b48c1b9
Now that #1313 is fixed, |= no longer outputs null when the RHS update expression outputs empty. When a user wants to keep the current value of the LHS they would have the RHS update expression output `.`, so having `empty` achieve the same thing would be redundant. The obvious thing to do is to delete the LHS when the RHS update outputs `empty` (i.e., doesn't output any values). It's reasonable to think that existing programs won't be broken by this change, because reduce and |= not handling empty well is clearly a bug. (Though it's possible that some programs were using empty to quickly terminate reduce or |=, it's not likely. They should use label/break instead.) Prior to this change |= would use the _last_ value output by the RHS update expression. With this change |= will use the _first_ value instead. This change _is_ a minor backwards-incompatible change. It may or may not be acceptable; we'll see. It is a useful change in that it makes |= faster when the update expression produces multiple values.
jq
jq is a lightweight and flexible command-line JSON processor.
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Unix: 
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Windows:
If you want to learn to use jq, read the documentation at https://stedolan.github.io/jq. This documentation is generated from the docs/ folder of this repository. You can also try it online at jqplay.org.
If you want to hack on jq, feel free, but be warned that its internals are not well-documented at the moment. Bring a hard hat and a shovel. Also, read the wiki: https://github.com/stedolan/jq/wiki
Source tarball and built executable releases can be found on the homepage and on the github release page, https://github.com/stedolan/jq/releases
If you're building directly from the latest git, you'll need flex, bison (3.0 or newer), libtool, make, and autoconf installed. To get regexp support you'll also need to install Oniguruma (note that jq's tests require regexp support to pass). To build, run:
autoreconf -i # if building from git
./configure
make -j8
make check
To build without bison or flex, add --disable-maintainer-mode to the
./configure invocation:
./configure --disable-maintainer-mode
(Developers must not use --disable-maintainer-mode, not when making
changes to the jq parser and/or lexer.)
To build a statically linked version of jq, run:
make LDFLAGS=-all-static
After make finishes, you'll be able to use ./jq. You can also
install it using:
sudo make install
If you're not using the latest git version but instead building a
released tarball (available on the website), then you won't need to
run autoreconf (and shouldn't), and you won't need flex or bison.
To cross-compile for OS X and Windows, see docs/Rakefile's build task and scripts/crosscompile. You'll need a cross-compilation environment, such as Mingw for cross-compiling for Windows.
Cross-compilation requires a clean workspace, then:
# git clean ...
autoreconf -i
./configure
make distclean
scripts/crosscompile <name-of-build> <configure-options>
Use the --host= and --target= ./configure options to select a cross-compilation environment. See also the wiki.
Send questions to https://stackoverflow.com/questions/tagged/jq or to the #jq channel (http://irc.lc/freenode/%23jq/) on Freenode (https://webchat.freenode.net/).