all: implement command to set environment value with "env-set"

The env-set command set the value of environment file. Syntax,

	<file> <key> <value>

The "file" argument define path to environment file.
The "key" argument define the key to be set using "section:sub:name"
format.
The "value" argument define the value key.

For example, to set the value for "name" under section "host" to
"myhost" in file "awwan.env" run

	$ awwan env-set awwan.env host::name myhost

To set the value for key "pass" under section "user" subsection "database"
to value "s3cret" in file "awwan.env" run

	$ awwan env-set awwan.env user:database:pass s3cret

1 files changed, 26 insertions, 0 deletions

diff --git a/testdata/env_set_test.data b/testdata/env_set_test.data
new file mode 100644
index 0000000..861a817
--- /dev/null
+++ b/testdata/env_set_test.data
@@ -0,0 +1,26 @@
+Test input and output for EnvSet.
+
+<<< withEmptyFile:error
+EnvSet: empty file argument
+
+<<< withEmptyKey:error
+EnvSet: empty key
+
+<<< withEmptyValue:error
+EnvSet: empty value
+
+<<< withMissingSection:error
+EnvSet: missing section in key
+
+<<< withMissingName:error
+EnvSet: missing name in key
+
+<<< withFileNotExist
+[host]
+name = awwan
+
+
+<<< withOverwriteValue
+[host]
+name = overwrite
+