Sed
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sed text editor
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To delete all lines matching a pattern:

.. code-block:: shell
    
    $cat file.txt | sed -e "/whatever/d"
    
Substituting a pattern by another

.. code-block:: shell
    
    $echo "pattern to chagne" | sed -e "s/gn/ng/g"

Some wildcards may be used, such as ^ that means the line start, $ that is the line end or that '.' means any character: