Simple script that allow read access to YAML files through command line.
This can be handy, if you want to get access to YAML data in your shell scripts.
This script supports only read access and it might not support all the subtleties of YAML specification. But it should support some handy basic query of YAML file.
shyaml works in Linux, MacOSX, and Windows with python 2.7 and 3+.
You don't need to download the GIT version of the code as shyaml is
available on the PyPI. So you should be able to run:
pip install shyaml
If you have downloaded the GIT sources, then you could add install the current version via:
pip install .
And if you don't have the GIT sources but would like to get the latest master or branch from github, you could also:
pip install git+https://github.com/0k/shyaml
Or even select a specific revision (branch/tag/commit):
pip install git+https://github.com/0k/shyaml@master
On macOS, you can also install the latest release version via Homebrew:
brew install shyaml
Or to install the master branch:
brew install shyaml --HEAD
The following documented examples are actually tested automatically at each release for conformance on all platform and python versions.
Please note that there is some subtle benign differences in some
output whether shyaml is using the libyaml C implementation or
the full python implementation. The documentation can be run with both
implementation but some examples will fail depending on the
implementation. To make things clear, I'll use some annotation and you
can yourself check which version you are using with:
$ shyaml -V | grep "^libyaml used:" ## docshtest: if-success-set LIBYAML libyaml used: True
shyaml takes its YAML input file from standard input ONLY. So let's
define here a common YAML input for the next examples:
$ cat <<EOF > test.yaml
name: "MyName !! héhé" ## using encoding, and support comments !
subvalue:
how-much: 1.1
how-many: 2
things:
- first
- second
- third
maintainer: "Valentin Lab"
description: |
Multiline description:
Line 1
Line 2
subvalue.how-much: 1.2
subvalue.how-much\more: 1.3
subvalue.how-much\.more: 1.4
EOF
Simple query of simple attribute:
$ cat test.yaml | shyaml get-value name MyName !! héhé
Query nested attributes by using '.' between key labels:
$ cat test.yaml | shyaml get-value subvalue.how-much 1.1
Get type of attributes:
$ cat test.yaml | shyaml get-type name str $ cat test.yaml | shyaml get-type subvalue.how-much float
Get length of structures or sequences:
$ cat test.yaml | shyaml get-length subvalue 5 $ cat test.yaml | shyaml get-length subvalue.things 3
But this won't work on other types:
$ cat test.yaml | shyaml get-length name Error: get-length does not support 'str' type. Please provide or select a sequence or struct.
Get sub YAML from a structure attribute:
$ cat test.yaml | shyaml get-type subvalue struct $ cat test.yaml | shyaml get-value subvalue ## docshtest: ignore-if LIBYAML how-much: 1.1 how-many: 2 things: - first - second - third maintainer: Valentin Lab description: 'Multiline description: Line 1 Line 2 '
Iteration through keys only:
$ cat test.yaml | shyaml keys name subvalue subvalue.how-much subvalue.how-much\more subvalue.how-much\.more
Iteration through keys only (\0 terminated strings):
$ cat test.yaml | shyaml keys-0 subvalue | xargs -0 -n 1 echo "VALUE:" VALUE: how-much VALUE: how-many VALUE: things VALUE: maintainer VALUE: description
Iteration through values only (\0 terminated string highly recommended):
$ cat test.yaml | shyaml values-0 subvalue |
while IFS='' read -r -d $'\0' value; do
echo "RECEIVED: '$value'"
done
RECEIVED: '1.1'
RECEIVED: '2'
RECEIVED: '- first
- second
- third
'
RECEIVED: 'Valentin Lab'
RECEIVED: 'Multiline description:
Line 1
Line 2
'
Iteration through keys and values (\0 terminated string highly recommended):
$ read-0() {
while [ "$1" ]; do
IFS=$'\0' read -r -d '' "$1" || return 1
shift
done
} &&
cat test.yaml | shyaml key-values-0 subvalue |
while read-0 key value; do
echo "KEY: '$key'"
echo "VALUE: '$value'"
echo
done
KEY: 'how-much'
VALUE: '1.1'
KEY: 'how-many'
VALUE: '2'
KEY: 'things'
VALUE: '- first
- second
- third
'
KEY: 'maintainer'
VALUE: 'Valentin Lab'
KEY: 'description'
VALUE: 'Multiline description:
Line 1
Line 2
'
<BLANKLINE>
Notice, that you'll get the same result using
get-values. get-values will support sequences and struct,
and key-values support only struct. (for a complete table of
which function support what you can look at the usage line)
And, if you ask for keys, values, key-values on non struct like, you'll get an error:
$ cat test.yaml | shyaml keys name Error: keys does not support 'str' type. Please provide or select a struct. $ cat test.yaml | shyaml values subvalue.how-many Error: values does not support 'int' type. Please provide or select a struct. $ cat test.yaml | shyaml key-values subvalue.how-much Error: key-values does not support 'float' type. Please provide or select a struct.
Query a sequence with get-value:
$ cat test.yaml | shyaml get-value subvalue.things - first - second - third
And access individual elements with python-like indexing:
$ cat test.yaml | shyaml get-value subvalue.things.0 first $ cat test.yaml | shyaml get-value subvalue.things.-1 third $ cat test.yaml | shyaml get-value subvalue.things.5 Error: invalid path 'subvalue.things.5', index 5 is out of range (3 elements in sequence).
Note that this will work only with integer (preceded or not by a minus sign):
$ cat test.yaml | shyaml get-value subvalue.things.foo Error: invalid path 'subvalue.things.foo', non-integer index 'foo' provided on a sequence.
More usefull, parse a list in one go with get-values:
$ cat test.yaml | shyaml get-values subvalue.things first second third
Note that the action is called get-values, and that output is
separated by newline char(s) (which is os dependent), this can bring
havoc if you are parsing values containing newlines itself. Hopefully,
shyaml has a get-values-0 to terminate strings by \0 char,
which allows complete support of any type of values, including YAML.
get-values outputs key and values for struct types and only
values for sequence types:
$ cat test.yaml | shyaml get-values-0 subvalue |
while IFS='' read -r -d '' key &&
IFS='' read -r -d '' value; do
echo "'$key' -> '$value'"
done
'how-much' -> '1.1'
'how-many' -> '2'
'things' -> '- first
- second
- third
'
'maintainer' -> 'Valentin Lab'
'description' -> 'Multiline description:
Line 1
Line 2
'
Please note that, if get-values{,-0} actually works on struct,
it's maybe more explicit to use the equivalent key-values{,0}. It
should be noted that key-values{,0} is not completly equivalent as
it is meant to be used with struct only and will complain if not.
You should also notice that values that are displayed are YAML compatible. So
if they are complex, you can re-use shyaml on them to parse their content.
Of course, get-values should only be called on sequence elements:
$ cat test.yaml | shyaml get-values name Error: get-values does not support 'str' type. Please provide or select a sequence or struct.
YAML input can be a stream of documents, the action will then be applied to each document:
$ i=0; while true; do
((i++))
echo "ingests:"
echo " - data: xxx"
echo " id: tag-$i"
if ((i >= 3)); then
break
fi
echo "---"
done | shyaml get-value ingests.0.id | tr '\0' '&'
tag-1&tag-2&tag-3
Notice that NUL char is used by default for separating output
iterations if not used in -y mode. You can use that to separate
each output. -y mode will use conventional YAML way to separate
documents (which is ---).
So:
$ i=0; while true; do
((i++))
echo "ingests:"
echo " - data: xxx"
echo " id: tag-$i"
if ((i >= 3)); then
break
fi
echo "---"
done | shyaml get-value -y ingests.0.id ## docshtest: ignore-if LIBYAML
tag-1
...
---
tag-2
...
---
tag-3
...
Notice that it is not supported to use any query that can output more than one
value (like all the query that can be suffixed with *-0) with a multi-document
YAML:
$ i=0; while true; do
((i++))
echo "ingests:"
echo " - data: xxx"
echo " id: tag-$i"
if ((i >= 3)); then
break
fi
echo "---"
done | shyaml keys ingests.0 >/dev/null
Error: Source YAML is multi-document, which doesn't support any other action than get-type, get-length, get-value
You'll probably notice also, that output seems buffered. The previous
content is displayed as a whole only at the end. If you need a
continuous flow of YAML document, then the command line option -L
is required to force a non-buffered line-by-line reading of the file
so as to ensure that each document is properly parsed as soon as
possible. That means as soon as either a YAML document end is detected
(--- or EOF):
Without the -L, if we kill our shyaml process before the end:
$ i=0; while true; do
((i++))
echo "ingests:"
echo " - data: xxx"
echo " id: tag-$i"
if ((i >= 2)); then
break
fi
echo "---"
sleep 10
done 2>/dev/null | shyaml get-value ingests.0.id & pid=$! ; sleep 2; kill $pid
With the -L, if we kill our shyaml process before the end:
$ i=0; while true; do
((i++))
echo "ingests:"
echo " - data: xxx"
echo " id: tag-$i"
if ((i >= 2)); then
break
fi
echo "---"
sleep 10
done 2>/dev/null | shyaml get-value -L ingests.0.id & pid=$! ; sleep 2; kill $pid
tag-1
Using -y is required to force a YAML output that will be also parseable as a stream,
which could help you chain shyaml calls:
$ i=0; while true; do
((i++))
echo "ingests:"
echo " - data: xxx"
echo " id: tag-$i"
if ((i >= 3)); then
break
fi
echo "---"
sleep 0.2
done | shyaml get-value ingests.0 -L -y | shyaml get-value id | tr '\0' '\n'
tag-1
tag-2
tag-3
An empty string will be still considered as an empty YAML document:
$ echo | shyaml get-value "toto" Error: invalid path 'toto', can't query subvalue 'toto' of a leaf (leaf value is None).
Use and \\ to access keys with \ and \. to access keys
with literal . in them. Just be mindful of shell escaping (example
uses single quotes):
$ cat test.yaml | shyaml get-value 'subvalue\.how-much' 1.2 $ cat test.yaml | shyaml get-value 'subvalue\.how-much\\more' 1.3 $ cat test.yaml | shyaml get-value 'subvalue\.how-much\\.more' default default
This last one didn't escape correctly the last ., this is the
correct version:
$ cat test.yaml | shyaml get-value 'subvalue\.how-much\\\.more' default 1.4
Yep, shyaml supports empty stringed keys. You might never have use
for this one, but it's in YAML specification. So shyaml supports
it:
$ cat <<EOF > test.yaml
empty-sub-key:
"":
a: foo
"": bar
"": wiz
EOF
$ cat test.yaml | shyaml get-value empty-sub-key..
bar
$ cat test.yaml | shyaml get-value ''
wiz
Please notice that one empty string is different than no string at all:
$ cat <<EOF > test.yaml "": a: foo b: bar "x": wiz EOF $ cat test.yaml | shyaml keys x $ cat test.yaml | shyaml keys '' a b
The first asks for keys of the root YAML, the second asks for keys of the content of the empty string named element located in the root YAML.
There is a third argument on the command line of shyaml which is the
DEFAULT argument. If the given KEY was not found in the YAML
structure, then shyaml would return what you provided as DEFAULT.
As of version < 0.3, this argument was defaulted to the empty string. For all version above 0.3 (included), if not provided, then an error message will be printed:
$ echo "a: 3" | shyaml get-value a mydefault 3 $ echo "a: 3" | shyaml get-value b mydefault mydefault $ echo "a: 3" | shyaml get-value b Error: invalid path 'b', missing key 'b' in struct.
You can emulate pre v0.3 behavior by specifying explicitly an empty string as third argument:
$ echo "a: 3" | shyaml get-value b ''
Starting with version 0.6, you can also use the -q or --quiet to fail
silently in case of KEY not found in the YAML structure:
$ echo "a: 3" | shyaml -q get-value b; echo "errlvl: $?" errlvl: 1 $ echo "a: 3" | shyaml -q get-value a; echo "errlvl: $?" 3errlvl: 0
Currently, using shyaml in a shell script involves happily taking
YAML inputs and outputting YAML outputs that will further be processed.
And this works very well.
Before version 0.4.0, shyaml would boldly re-order (sorting them
alphabetically) the keys in mappings. If this should be considered
harmless per specification (mappings are indeed supposed to be
unordered, this means order does not matter), in practical, YAML users
could feel wronged by shyaml when there YAML got mangled and they
wanted to give a meaning to the basic YAML mapping.
Who am I to forbid such usage of YAML mappings ? So starting from
version 0.4.0, shyaml will happily keep the order of your
mappings:
$ cat <<EOF > test.yaml mapping: a: 1 c: 2 b: 3 EOF
For shyaml version before 0.4.0:
# shyaml get-value mapping < test.yaml a: 1 b: 3 c: 2
For shyaml version including and after 0.4.0:
$ shyaml get-value mapping < test.yaml a: 1 c: 2 b: 3
Processing yaml can be done recursively and extensively through using
the output of shyaml into shyaml. Most of its output is itself
YAML. Most ? Well, for ease of use, literal keys (string, numbers) are
outputed directly without YAML quotes, which is often convenient.
But this has the consequence of introducing inconsistent behavior. So
when processing YAML coming out of shyaml, you should probably think
about using the --yaml (or -y) option to output only strict YAML.
With the drawback that when you'll want to output string, you'll need to
call a last time shyaml get-value to explicitly unquote the YAML.
YAML spec allows object tags which allows you to map local data to objects in your application.
When using shyaml, we do not want to mess with these tags, but still
allow parsing their internal structure.
get-type will correctly give you the type of the object:
$ cat <<EOF > test.yaml %TAG !e! tag:example.com,2000:app/ --- - !e!foo "bar" EOF $ shyaml get-type 0 < test.yaml tag:example.com,2000:app/foo
get-value with -y (see section Strict YAML) will give you the
complete yaml tagged value:
$ shyaml get-value -y 0 < test.yaml ## docshtest: ignore-if LIBYAML !<tag:example.com,2000:app/foo> 'bar'
Another example:
$ cat <<EOF > test.yaml
%TAG ! tag:clarkevans.com,2002:
--- !shape
# Use the ! handle for presenting
# tag:clarkevans.com,2002:circle
- !circle
center: &ORIGIN {x: 73, y: 129}
radius: 7
- !line
start: *ORIGIN
finish: { x: 89, y: 102 }
- !label
start: *ORIGIN
color: 0xFFEEBB
text: Pretty vector drawing.
EOF
$ shyaml get-type 2 < test.yaml
tag:clarkevans.com,2002:label
And you can still traverse internal value:
$ shyaml get-value -y 2.start < test.yaml x: 73 y: 129
Note that all global tags will be resolved and simplified (as
!!map, !!str, !!seq), but not unknown local tags:
$ cat <<EOF > test.yaml
%YAML 1.1
---
!!map {
? !!str "sequence"
: !!seq [ !!str "one", !!str "two" ],
? !!str "mapping"
: !!map {
? !!str "sky" : !myobj "blue",
? !!str "sea" : !!str "green",
},
}
EOF
$ shyaml get-value < test.yaml ## docshtest: ignore-if LIBYAML
sequence:
- one
- two
mapping:
sky: !myobj 'blue'
sea: green
When provided with an empty document, shyaml will consider the
document to hold a null value:
$ echo | shyaml get-value -y ## docshtest: ignore-if LIBYAML null ...
A quick reminder of what is available will be printed when calling
shyaml without any argument:
$ shyaml
Error: Bad number of arguments.
Usage:
shyaml {-h|--help}
shyaml {-V|--version}
shyaml [-y|--yaml] [-q|--quiet] ACTION KEY [DEFAULT]
<BLANKLINE>
The full help is available through the usage of the standard -h or
-help:
$ shyaml --help
Parses and output chosen subpart or values from YAML input.
It reads YAML in stdin and will output on stdout it's return value.
Usage:
shyaml {-h|--help}
shyaml {-V|--version}
shyaml [-y|--yaml] [-q|--quiet] ACTION KEY [DEFAULT]
Options:
-y, --yaml
Output only YAML safe value, more precisely, even
literal values will be YAML quoted. This behavior
is required if you want to output YAML subparts and
further process it. If you know you have are dealing
with safe literal value, then you don't need this.
(Default: no safe YAML output)
-q, --quiet
In case KEY value queried is an invalid path, quiet
mode will prevent the writing of an error message on
standard error.
(Default: no quiet mode)
-L, --line-buffer
Force parsing stdin line by line allowing to process
streamed YAML as it is fed instead of buffering
input and treating several YAML streamed document
at once. This is likely to have some small performance
hit if you have a huge stream of YAML document, but
then you probably don't really care about the
line-buffering.
(Default: no line buffering)
ACTION Depending on the type of data you've targetted
thanks to the KEY, ACTION can be:
These ACTIONs applies to any YAML type:
get-type ## returns a short string
get-value ## returns YAML
These ACTIONs applies to 'sequence' and 'struct' YAML type:
get-values{,-0} ## returns list of YAML
get-length ## returns an integer
These ACTION applies to 'struct' YAML type:
keys{,-0} ## returns list of YAML
values{,-0} ## returns list of YAML
key-values,{,-0} ## returns list of YAML
Note that any value returned is returned on stdout, and
when returning ``list of YAML``, it'll be separated by
a newline or ``NUL`` char depending of you've used the
``-0`` suffixed ACTION.
KEY Identifier to browse and target subvalues into YAML
structure. Use ``.`` to parse a subvalue. If you need
to use a literal ``.`` or ``\``, use ``\`` to quote it.
Use struct keyword to browse ``struct`` YAML data and use
integers to browse ``sequence`` YAML data.
DEFAULT if not provided and given KEY do not match any value in
the provided YAML, then DEFAULT will be returned. If no
default is provided and the KEY do not match any value
in the provided YAML, shyaml will fail with an error
message.
Examples:
## get last grocery
cat recipe.yaml | shyaml get-value groceries.-1
## get all words of my french dictionary
cat dictionaries.yaml | shyaml keys-0 french.dictionary
## get YAML config part of 'myhost'
cat hosts_config.yaml | shyaml get-value cfgs.myhost
<BLANKLINE>
Using invalid keywords will issue an error and the usage message:
$ shyaml get-foo
Error: 'get-foo' is not a valid action.
Usage:
shyaml {-h|--help}
shyaml {-V|--version}
shyaml [-y|--yaml] [-q|--quiet] ACTION KEY [DEFAULT]
<BLANKLINE>
You can get useful information (in case of a bug) or if you want to
check if shyaml is using the libyaml C bindings, thanks to
shyaml --version (or -V):
# shyaml -V ## Example of possible output version: unreleased PyYAML: 3.13 libyaml available: 0.1.6 libyaml used: True Python: 2.7.8 (default, Oct 20 2014, 15:05:19) [GCC 4.9.1]
Note that you can force to use the python implementation even if
libyaml is available using FORCE_PYTHON_YAML_IMPLEMENTATION:
$ FORCE_PYTHON_YAML_IMPLEMENTATION=1 shyaml --version | grep "^libyaml used:" libyaml used: False
shyaml can be used from within python if you need so:
>>> import shyaml
>>> try:
... from StringIO import StringIO
... except ImportError:
... from io import StringIO
>>> yaml_content = StringIO("""
... a: 1.1
... b:
... x: foo
... y: bar
... """)
>>> for out in shyaml.do(stream=yaml_content,
... action="get-type",
... key="a"):
... print(repr(out))
'float'
Please note that shyaml.do(..) outputs a generator iterating
through all the yaml documents of the stream. In most usage case,
you'll have only one document.
You can have a peek at the code, the do(..) function has a documented
prototype.
Any suggestion or issue is welcome. Push request are very welcome, please check out the guidelines.
You can send any code. I'll look at it and will integrate it myself in the code base and leave you as the author. This process can take time and it'll take less time if you follow the following guidelines:
- check your code with PEP8 or pylint. Try to stick to 80 columns wide.
- separate your commits per smallest concern.
- each commit should pass the tests (to allow easy bisect)
- each functionality/bugfix commit should contain the code, tests, and doc.
- prior minor commit with typographic or code cosmetic changes are
very welcome. These should be tagged in their commit summary with
!minor. - the commit message should follow gitchangelog rules (check the git log to get examples)
- if the commit fixes an issue or finished the implementation of a feature, please mention it in the summary.
If you have some questions about guidelines which is not answered here,
please check the current git log, you might find previous commit that
would show you how to deal with your issue.
Copyright (c) 2020 Valentin Lab.
Licensed under the BSD License.
