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We need to be careful to not grab an extra reference when mutating data
structures because that means we make extra copies.  Doing that every
time in `_modify` is really painful, as that function implements `|=`
and all modify-assign operators.

`jv_setpath()` also grabs additional references, so this is not the only
fix needed for the modify-assign operators to not be accidentally
quadratic.

We have to use `LOADVN` in order to make this fix possible, so we should
really byte-code `_modify` rather than jq-code it.  However, as a
stop-gap to make this fix easier, I'm adding syntax for referring to a
`$binding` such that you get `LOADVN` instead of `LOADV`.

This syntax is not meant to be used outside jq's internals!  Therefore
it is not documented.  I promise to break it later, so don't use it!

TBD, but later:

 - Optimize `_modify` for the case where `update` outputs more than one
   value.

   This is trivial: add a `setpath($p; null)` in the middle of `_modify`
   before calling `update`.  But unfortunately the VM retains a
   reference to `value_at_path` for path expression checking, and fixing
   that will require more work.
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jq

jq is a lightweight and flexible command-line JSON processor.

Coverage Status, Unix: Build Status, Windows: Windows build status

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, where you will find cookbooks, discussion of advanced topics, internals, release engineering, and more.

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, automake, and autoconf installed. To get regexp support you'll also need to install Oniguruma or clone it as a git submodule as per the instructions below. (note that jq's tests require regexp support to pass). To build, run:

git submodule update --init # if building from git to get oniguruma
autoreconf -fi              # if building from git
./configure --with-oniguruma=builtin
make -j8
make check

To build without bison or flex, add --disable-maintainer-mode to the ./configure invocation:

./configure --with-oniguruma=builtin --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 "Cross compilation" on 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/).