Another complex combination.  To list line numbers on a file the cat command has an option, but the “nl” command has multiple formating options, something that the “cat” command doesnt.The -n specifies a format and “rz” right justifies with not leading zeros.
cat sourcefile.php | nl -n rz
To see the last 3 lines of any text [...]

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The scenario is that you have a compressed file with ZIP, and this is a raw text log file that you have to unzip and then to cat.
$ zcat messages.gz
You want to see only the first lines of a text file, for that is the head command.
$ head messages.log
And if you want to see the [...]

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Removing repeated lines in a text, the strategy to remove repeated lines in a text is not very intuitive at the first, the operation is divided in parts:
1) convert if possible all the lines to lowercase.2) sort the lines so repeated lines are together.3) remove repeated lines.

$ cat file1.txt file2.txt file3.txt | tr [A-Z] [a-z] [...]

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