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+.. link:
+.. description: is a unix tool aiding the Telefonbuch project for export and search queries.
+.. tags: project
+.. date: 2015/02/01 19:10:08
+.. title: el
+.. subtitle: extract lines from text files
+.. slug: ../arts/software/el/index
+.. prio: 100
+
+.. contents::
+  :depth: 1
+  :class: ezjail-toc
+
+----
+
+Overview
+========
+
+*el* (from extract lines) is a unix tool to efficiently extract lines from a text file using a dynamic line end index. Its command line syntax is tuned to work with other posix tools – especially grep – to easily operate on poor man's databases where each of the database's columns is in a separate newline separated file.
+
+Since *el* mmaps the whole file, it does not work on streams.
+
+----
+
+Build instructions
+==================
+
+Get the source from my git repository ``git clone git://erdgeist.org/el`` and type ``make`` in the directory ``el``. *el* has no further dependencies and can just be copied to ``/usr/local/bin`` or wherever your binaries reside.
+
+----
+
+Invocation
+==========
+
+In its simplest form just run::
+
+  echo 1 2 3 4 5 6 7 8 9 10 | el file.txt
+
+to extract lines 1 to 10 from the file ``file.txt`` and print them to stdout. *el* also accepts white space separated line numbers with the ``-i`` parameter and can default to hexadecimal numbers with the ``-x`` switch::
+
+  el -i "10 11 12 13" -x file1.txt file2.txt
+
+extracts line 16 to 19 from the files ``file.txt`` and ``file2.txt``, each line separated by the tab character. If your line numbers start at ``0``, *el* will add 1, if it is run with the ``-0`` switch.
+
+The reason reading line numbers from stdin and not from command line by default becomes apparent, when you use the combining features of *el*, as it can parse and generate output as the ``grep`` posix tool does.
+
+If you use the ``-n`` switch, each extracted line is prefixed by it's line number and a colon, just as ``grep`` does. If you use the ``-g`` switch, *el* will also **expect** the line numbers on stdin to be terminated by a colon followed by garbage until next newline. So you can feed results from ``grep -n`` directly to it. With the ``-G`` option, not only will *el* parse the line numbers from ``grep``'s output, but also append the extracted lines from each file to the input line. In order to chain several ``grep`` and *el* commands, best combine the ``-Gn`` switches as in this example::
+
+  grep -n Manager positions.txt | el -Gn firstname.txt lastname.txt | grep Jon | el -Gn salary.txt
+
+This will produce, an output like this::
+
+  17:Manager\tJon\tMiller\t$1200
+  23:Manager\tJon\tDoe\t$1600
+
+given that all the text files contain corresponding rows of information about the staff.
+
+----
+
+Author
+======
+
+*el* was written by `Dirk Engling <mailto:erdgeist@erdgeist.org>`_, who likes to hear from happy customers.
+
+----
+
+License
+=======
+
+*el* is considered `beer ware </beerware.html>`_.
+
+