Added preliminary xargs presentation

kiloforce · Nov 14, 2010 · 604c915 · 604c915
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diff --git a/oalug_2011-02-22_xargs/presentation.rst b/oalug_2011-02-22_xargs/presentation.rst
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+===========================
+Ogden Area Linux User Group
+===========================
+xargs
+=====
+
+:Author:    Seth House <seth@eseth.com>
+:Date:      2011-02-22
+
+
+srs? A whole presentation just on xargs?
+========================================
+
+That’s right.
+
+Baby steps
+==========
+
+.. class:: handout
+
+    ``-t``
+        Synonym for --verbose. Output the command about to be executed.
+
+If not given a command, ``xargs`` assumes ``echo``::
+
+    ls *.foo | xargs
+    ls *.foo | xargs -t
+
+Prompt before running the command::
+
+    ls *.foo | xargs -p
+
+Why is that useful?
+===================
+
+Get a list of process IDs::
+
+    pgrep ssh
+
+Get info on a list of process IDs::
+
+    pgrep ssh | xargs ps
+
+Handle arguments in groups
+==========================
+
+All at once::
+
+    echo 1 2 3 4 | xargs
+
+One at a time::
+
+    echo 1 2 3 4 | xargs -n1
+
+In groups of two::
+
+    echo 1 2 3 4 | xargs -n2
+
+Call programs that take multiple arguments
+==========================================
+
+.. class:: handout
+
+    ``-I``
+        replace-string
+
+::
+
+    ls *.foo | xargs -n1 -I@ cp @ ~/mybackups
+
+On-the-fly shell scripts (that take arguments!)
+===============================================
+
+.. class:: handout
+
+    ``-n1``
+        Handle input one-at-a-time.
+    ``-``
+        Pass stdin as an argument to the script. This gives access to
+        shell-script positional parameters like ``$@`` and ``$*``.
+
+Use ``xargs`` to invoke ``sh -c`` and have access to positional parameters::
+
+    ls *.foo | xargs -n1 sh -c 'echo $1' -
+
+Parallel execution
+==================
+
+.. class:: handout
+
+    ``-P``
+        Specify the number of processes to start.
+    ``-d``
+        Specify the delimeter to look for in the input.
+
+    I used to just use a for-loop::
+
+        for ip in 192.168.0.{1..5}; do ssh $ip 'cd /some/path; git rev-list HEAD -n 1'; done
+
+    But executing in parallel is much faster for large numbers of machines::
+
+        echo -n 192.168.0.{1..50} | xargs -P10 ...
+
+Get the load for several machines::
+
+    echo -n 192.168.0.{1..5} | xargs -P5 -n1 -d" " -I"HOST" sh -c 'ssh -T HOST uptime'
+    echo -n 192.168.0.{1..5} | xargs -P5 -n1 -d" " -I"HOST" sh -c 'ssh -T HOST uptime | sed -e "s/^/HOST: /"'
+
+
+Parallelize grep
+================
+
+.. class:: handout
+
+    http://blog.labrat.info/20100429/using-xargs-to-do-parallel-processing/
+
+    Ideally you would calculate the number of cores for the -P argument::
+
+        cat /proc/cpuinfo | grep processor | wc -l
+
+If you need to grep though a large directory structure it can be parallelized!
+Create 4 processes each one looking at 10 files::
+
+    find /some/path -type f | xargs -P 4 -n 10 grep -H 'string-to-search'
+
+Convert several files to pdf simultaneously
+===========================================
+
+Regular::
+
+    find ./ -name "*.pdf" | xargs -Istr pdf2ps str
+
+Fast::
+
+    find ./ -name "*.pdf" | xargs -n 8 -Istr pdf2ps str