nl Command in Linux: Number Lines in Text Files in Terminal

The nl command in Linux (number lines) is used to number the lines of a file. The command considers special conditions for the header and footer of the file.

The frequently used options are:

• -h sub-option: Used to format the text header. The default is not to number the header;
• -b sub-option: Used to format the body of the text. The default is to number only non-empty lines;
• -f sub-option: Used to format the text footer. The default is not to number the footer.

The sub-options are:

• A: Number all lines;
• t: Number only the filled ones;
• n: Do not number the lines.

Example:

Suppose that arquivo.txt has the following content:

\:\:\:
Relatório de Notas e Frequência dos alunos de Engenharia de Software
—————————————————————————————————
Nome Nota Freq. Resultado
—————————————————————————————————
\:\:
Carlos Torres 8,5 80% Aprovado
José Antônio 10,0 100% Aprovado
Maria de Lourdes 10,0 100% Aprovado
Mário Cabral 9,5 100% Aprovado
\:
—————————————————————————————————

And using the nl command:

$ nl arquivo.txt

The result will be:

Relatório de Notas e Frequência dos alunos de Engenharia de Software—————————————————————————————————Nome Nota Freq. Resultado—————————————————————————————————1 Carlos Torres 8,5 80% Aprovado2 José Antônio 10,0 100% Aprovado3 Maria de Lourdes 10,0 100% Aprovado4 Mário Cabral 9,5 100% Aprovado—————————————————————————————————

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