Document distinction between file and tail inputs (#7353)

plugins/inputs/file/README.md

@@ -1,22 +1,18 @@
 # File Input Plugin
 
-The file plugin updates a list of files every interval and parses the contents
-using the selected [input data format](/docs/DATA_FORMATS_INPUT.md).
+The file plugin parses the **complete** contents of a file **every interval** using
+the selected [input data format][].
 
-Files will always be read in their entirety, if you wish to tail/follow a file
-use the [tail input plugin](/plugins/inputs/tail) instead.
+**Note:** If you wish to parse only newly appended lines use the [tail][] input
+plugin instead.
 
 ### Configuration:
 
 ```toml
 [[inputs.file]]
-  ## Files to parse each interval.
-  ## These accept standard unix glob matching rules, but with the addition of
-  ## ** as a "super asterisk". ie:
-  ##   /var/log/**.log     -> recursively find all .log files in /var/log
-  ##   /var/log/*/*.log    -> find all .log files with a parent dir in /var/log
-  ##   /var/log/apache.log -> only read the apache log file
-  files = ["/var/log/apache/access.log"]
+  ## Files to parse each interval.  Accept standard unix glob matching rules,
+  ## as well as ** to match recursive files and directories.
+  files = ["/tmp/metrics.out"]
 
   ## Data format to consume.
   ## Each data format has its own unique set of configuration options, read
@@ -28,3 +24,6 @@ use the [tail input plugin](/plugins/inputs/tail) instead.
   ## to disable.
   # file_tag = ""
 ```
+
+[input data format]: /docs/DATA_FORMATS_INPUT.md
+[tail]: /plugins/inputs/tail

plugins/inputs/file/file.go

@@ -20,13 +20,9 @@ type File struct {
 }
 
 const sampleConfig = `
-  ## Files to parse each interval.
-  ## These accept standard unix glob matching rules, but with the addition of
-  ## ** as a "super asterisk". ie:
-  ##   /var/log/**.log     -> recursively find all .log files in /var/log
-  ##   /var/log/*/*.log    -> find all .log files with a parent dir in /var/log
-  ##   /var/log/apache.log -> only read the apache log file
-  files = ["/var/log/apache/access.log"]
+  ## Files to parse each interval.  Accept standard unix glob matching rules,
+  ## as well as ** to match recursive files and directories.
+  files = ["/tmp/metrics.out"]
 
   ## The dataformat to be read from files
   ## Each data format has its own unique set of configuration options, read
@@ -45,7 +41,7 @@ func (f *File) SampleConfig() string {
 }
 
 func (f *File) Description() string {
-	return "Reload and gather from file[s] on telegraf's interval."
+	return "Parse a complete file each interval"
 }
 
 func (f *File) Gather(acc telegraf.Accumulator) error {

plugins/inputs/tail/tail.go

@@ -100,7 +100,7 @@ func (t *Tail) SampleConfig() string {
 }
 
 func (t *Tail) Description() string {
-	return "Stream a log file, like the tail -f command"
+	return "Parse the new lines appended to a file"
 }
 
 func (t *Tail) Init() error {