webghostx · December 20, 2024 08:30 · Jun 4, 2015
diff --git a/yaml_parser.md b/yaml_parser.md
@@ -0,0 +1,97 @@
+Found [here](http://stackoverflow.com/questions/5014632/how-can-i-parse-a-yaml-file-from-a-linux-shell-script/21189044#21189044) by [Stephan Farestam](http://stackoverflow.com/users/1792684/stefan-farestam)
+
+Here is a bash-only YAML parser that leverages sed and awk to parse simple yaml files:
+
+    function parse_yaml {
+       local prefix=$2
+       local s='[[:space:]]*' w='[a-zA-Z0-9_]*' fs=$(echo @|tr @ '\034')
+       sed -ne "s|^\($s\):|\1|" \
+            -e "s|^\($s\)\($w\)$s:$s[\"']\(.*\)[\"']$s\$|\1$fs\2$fs\3|p" \
+            -e "s|^\($s\)\($w\)$s:$s\(.*\)$s\$|\1$fs\2$fs\3|p"  $1 |
+       awk -F$fs '{
+          indent = length($1)/2;
+          vname[indent] = $2;
+          for (i in vname) {if (i > indent) {delete vname[i]}}
+          if (length($3) > 0) {
+             vn=""; for (i=0; i<indent; i++) {vn=(vn)(vname[i])("_")}
+             printf("%s%s%s=\"%s\"\n", "'$prefix'",vn, $2, $3);
+          }
+       }'
+    }
+
+It understands files such as:
+
+    ## global definitions
+    global:
+      debug: yes
+      verbose: no
+      debugging:
+        detailed: no
+        header: "debugging started"
+
+    ## output
+    output:
+       file: "yes"
+
+
+Which, when parsed using:
+
+    parse_yaml sample.yml
+
+will output: 
+
+    global_debug="yes"
+    global_verbose="no"
+    global_debugging_detailed="no"
+    global_debugging_header="debugging started"
+    output_file="yes"
+
+it also understands yaml files, generated by ruby which may include ruby symbols, like:
+
+    ---
+    :global:
+      :debug: 'yes'
+      :verbose: 'no'
+      :debugging:
+        :detailed: 'no'
+        :header: debugging started
+      :output: 'yes'
+
+and will output the same as in the previous example.
+
+typical use within a script is:
+
+    eval $(parse_yaml sample.yml)
+
+parse_yaml accepts a prefix argument so that imported settings all have a common prefix (which will reduce the risk of namespace collisions).
+
+    parse_yaml sample.yml "CONF_"
+
+yields:
+
+    CONF_global_debug="yes"
+    CONF_global_verbose="no"
+    CONF_global_debugging_detailed="no"
+    CONF_global_debugging_header="debugging started"
+    CONF_output_file="yes"
+
+Note that previous settings in a file can be referred to by later settings:
+
+    ## global definitions
+    global:
+      debug: yes
+      verbose: no
+      debugging:
+        detailed: no
+        header: "debugging started"
+
+    ## output
+    output:
+       debug: $global_debug
+
+Another nice usage is to first parse a defaults file and then the user settings, which works since the latter settings overrides the first ones:
+
+    eval $(parse_yaml defaults.yml)
+    eval $(parse_yaml project.yml)
+
+
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