README.md
1jWalterWeatherman
2=================
3
4Seamless printing to the terminal (stdout) and logging to a io.Writer
5(file) that’s as easy to use as fmt.Println.
6
7
8Graphic by [JonnyEtc](http://jonnyetc.deviantart.com/art/And-That-s-Why-You-Always-Leave-a-Note-315311422)
9
10JWW is primarily a wrapper around the excellent standard log library. It
11provides a few advantages over using the standard log library alone.
12
131. Ready to go out of the box.
142. One library for both printing to the terminal and logging (to files).
153. Really easy to log to either a temp file or a file you specify.
16
17
18I really wanted a very straightforward library that could seamlessly do
19the following things.
20
211. Replace all the println, printf, etc statements thoughout my code with
22 something more useful
232. Allow the user to easily control what levels are printed to stdout
243. Allow the user to easily control what levels are logged
254. Provide an easy mechanism (like fmt.Println) to print info to the user
26 which can be easily logged as well
275. Due to 2 & 3 provide easy verbose mode for output and logs
286. Not have any unnecessary initialization cruft. Just use it.
29
30# Usage
31
32## Step 1. Use it
33Put calls throughout your source based on type of feedback.
34No initialization or setup needs to happen. Just start calling things.
35
36Available Loggers are:
37
38 * TRACE
39 * DEBUG
40 * INFO
41 * WARN
42 * ERROR
43 * CRITICAL
44 * FATAL
45
46These each are loggers based on the log standard library and follow the
47standard usage. Eg.
48
49```go
50 import (
51 jww "github.com/spf13/jwalterweatherman"
52 )
53
54 ...
55
56 if err != nil {
57
58 // This is a pretty serious error and the user should know about
59 // it. It will be printed to the terminal as well as logged under the
60 // default thresholds.
61
62 jww.ERROR.Println(err)
63 }
64
65 if err2 != nil {
66 // This error isn’t going to materially change the behavior of the
67 // application, but it’s something that may not be what the user
68 // expects. Under the default thresholds, Warn will be logged, but
69 // not printed to the terminal.
70
71 jww.WARN.Println(err2)
72 }
73
74 // Information that’s relevant to what’s happening, but not very
75 // important for the user. Under the default thresholds this will be
76 // discarded.
77
78 jww.INFO.Printf("information %q", response)
79
80```
81
82NOTE: You can also use the library in a non-global setting by creating an instance of a Notebook:
83
84```go
85notepad = jww.NewNotepad(jww.LevelInfo, jww.LevelTrace, os.Stdout, ioutil.Discard, "", log.Ldate|log.Ltime)
86notepad.WARN.Println("Some warning"")
87```
88
89_Why 7 levels?_
90
91Maybe you think that 7 levels are too much for any application... and you
92are probably correct. Just because there are seven levels doesn’t mean
93that you should be using all 7 levels. Pick the right set for your needs.
94Remember they only have to mean something to your project.
95
96## Step 2. Optionally configure JWW
97
98Under the default thresholds :
99
100 * Debug, Trace & Info goto /dev/null
101 * Warn and above is logged (when a log file/io.Writer is provided)
102 * Error and above is printed to the terminal (stdout)
103
104### Changing the thresholds
105
106The threshold can be changed at any time, but will only affect calls that
107execute after the change was made.
108
109This is very useful if your application has a verbose mode. Of course you
110can decide what verbose means to you or even have multiple levels of
111verbosity.
112
113
114```go
115 import (
116 jww "github.com/spf13/jwalterweatherman"
117 )
118
119 if Verbose {
120 jww.SetLogThreshold(jww.LevelTrace)
121 jww.SetStdoutThreshold(jww.LevelInfo)
122 }
123```
124
125Note that JWW's own internal output uses log levels as well, so set the log
126level before making any other calls if you want to see what it's up to.
127
128
129### Setting a log file
130
131JWW can log to any `io.Writer`:
132
133
134```go
135
136 jww.SetLogOutput(customWriter)
137
138```
139
140
141# More information
142
143This is an early release. I’ve been using it for a while and this is the
144third interface I’ve tried. I like this one pretty well, but no guarantees
145that it won’t change a bit.
146
147I wrote this for use in [hugo](https://gohugo.io). If you are looking
148for a static website engine that’s super fast please checkout Hugo.
149
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