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Is possible, with fmt.Println("...") to print a string with center alignement of the shell?

sensorario
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    So do you know the width of the shell or is that part of what you need to work out how to do? – miltonb Dec 14 '16 at 02:06
  • This can tell you the width and height: http://stackoverflow.com/questions/263890/how-do-i-find-the-width-height-of-a-terminal-window – miltonb Dec 14 '16 at 02:53
  • @miltonb, your link is for bash, ... can I use bash from go? – sensorario Dec 14 '16 at 11:08
  • Yes, you can make a call to OS using `os/exec` package. It will take some lines of code based around `exec.Command()`. – miltonb Dec 14 '16 at 19:38

2 Answers2

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As an update to this long-answered question, the solution posted by @miltonb can be improved upon by using the * notation from the fmt package. From the package documentation:

In Printf, Sprintf, and Fprintf, the default behavior is for each formatting verb to format successive arguments passed in the call. However, the notation [n] immediately before the verb indicates that the nth one-indexed argument is to be formatted instead. The same notation before a '*' for a width or precision selects the argument index holding the value. After processing a bracketed expression [n], subsequent verbs will use arguments n+1, n+2, etc. unless otherwise directed.

So you can replace two of the fmt.Sprintf calls with a more concise format statement to achieve the same result:

s := "in the middle"
w := 110 // or whatever

fmt.Sprintf("%[1]*s", -w, fmt.Sprintf("%[1]*s", (w + len(s))/2, s))

See the code in action.

Additionally, as @chris-dennis mentioned, the [1] notation is superfluous in this example because the width of the string is already the first argument. This works as well:

fmt.Sprintf("%*s", -w, fmt.Sprintf("%*s", (w + len(s))/2, s))

See this example in action.

PaSTE
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This code is managing to centre the text as long as the shell width is a known value. Its not quite 'pixel perfect', but I hope it helps.

If we break it down there are two bits of code to produce the format strings to pad right and then left.

fmt.Sprintf("%%-%ds", w/2)  // produces "%-55s"  which is pad left string
fmt.Sprintf("%%%ds", w/2)   // produces "%55s"   which is right pad

So the final Printf statement becomes

fmt.Printf("%-55s", fmt.Sprintf("%55s", "my string to centre"))

The full code:

s := " in the middle"
w := 110 // shell width

fmt.Printf(fmt.Sprintf("%%-%ds", w/2), fmt.Sprintf(fmt.Sprintf("%%%ds", w/2),s))

Produces the following:

                                     in the middle

Link to play ground: play

miltonb
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  • I've seen. But could you explain a bit "%%-%ds"? Doc says `%% a literal percent sign; consumes no value` what exactly means? `%d is for digit`. – sensorario Dec 14 '16 at 11:21
  • Updated with better description of the code to produce the format strings. – miltonb Dec 14 '16 at 19:33
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    I think there's a bug in the solution code, as it does not take into account the width of the string `s`. See the modified playground code at https://play.golang.org/p/8L5IfEIKSS. I think you need to replace the first `w/2` with a `w` and the second with a `(w + len(s))/2`, as shown in my answer below. – PaSTE Dec 14 '17 at 23:20