SPRINTF in shell scripting?

Question

I have an auto-generated file each day that gets called by a shell script. But, the problem I'm facing is that the auto-generated file has a form of: ``` FILE_MM_DD.dat ``` ... where MM and DD are 2-digit month and day-of-the-month strings. I did some research and banged it at on my own, but I don't know how to create these custom strings using only shell scripting. To be clear, I am aware of the DATE function in Bash, but what I'm looking for is the equivalent of the SPRINTF function in C.

Accepted Answer

In Bash:

```
var=$(printf 'FILE=_%s_%s.dat' "$val1" "$val2")
```

or, the equivalent, and closer to `sprintf`:

```
printf -v var 'FILE=_%s_%s.dat' "$val1" "$val2"
```

If your variables contain decimal values with leading zeros, you can remove the leading zeros:

```
val1=008; val2=02
var=$(printf 'FILE=_%d_%d.dat' $((10#$val1)) $((10#$val2)))
```

or

```
printf -v var 'FILE=_%d_%d.dat' $((10#$val1)) $((10#$val2))
```

The `$((10#$val1))` coerces the value into base 10 so the `%d` in the format specification doesn't think that "08" is an invalid octal value.

If you're using `date` (at least for GNU `date`), you can omit the leading zeros like this:

```
date '+FILE_%-m_%-d.dat'
```

For completeness, if you want to add leading zeros, padded to a certain width:

```
val1=8; val2=2
printf -v var 'FILE=_%04d_%06d.dat' "$val1" "$val2"
```

or with dynamic widths:

```
val1=8; val2=2
width1=4; width2=6
printf -v var 'FILE=_%0*d_%0*d.dat' "$width1" "$val1" "$width2" "$val2"
```

Adding leading zeros is useful for creating values that sort easily and align neatly in columns.

SPRINTF in shell scripting?

Solution

Problem