# underscore

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## 1 latex underscore

Setting an underscore _ in LaTeX is not that easy. Since this is a reserved special character. The underscore is used within math mode for setting indices, so \$a_{i}\$ becomes ai. To use the underscore within the normal text mode, it must be masked with a backslash, then the underscore _ is set with \_. If the underscore is not masked, the following error message is displayed:
```!Missing \$ inserted.
<inserted text>
\$
```
In the event that the underscore is often used at the document, masking can become quite cumbersome. In such a case you can use the package underscore.

## 2 underscore Package

The underscore package (version 1.0) from 2006 provides a modified version of the underscore.
The package is integrated with: \usepackage{underscore}

The advantage of the package is that the underscore can now be used as a simple keyboard character _ within text mode and the underscore can still be used in math mode to introduce the indices.

Input:
```Word_Word \$a_{i}\$
```
Output:
Word_Word ai

Using the underscore package has the disadvantage that no external file (images, additional tex file) can be included if it contains a _ in file names. This means that within the commands \input{filename}, \include{filename} and \includegraphics{filename} no filename with an underscore can be used. In addition, problems can also be expected with other commands if an underscore is used.

#### 2.2.1 Option strings

If the package option strings is set, some of the above problems will be fixed and at \input{filename} and \include{filename} filenames with underscore can be used again.

Set the option strings: \usepackage[strings]{underscore}

### 2.3 Conclusion

Bepart from the new problem, i.e. the limited use of the underscore in file names and commands, the package is a viable alternative to masking each underscore.

## 3 latex underline

Eng related to the question nor the underscore is the underlining of words, words and paragraphs. If a word is to be underlined, the default LaTeX command \underline{word} can be used, or the \ul{word} command from the soul package. If a whole paragraph is to be underlined, the \uline{paragraph} from the ulem package can be used.

Source:https://www.ctan.org/pkg/underscore