initial version of diff command wrapper

tools/diff/.shed.yml

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+categories:
+- Text Manipulation
+description: GNU diff tool that calculates the differences between two files.
+homepage_url: http://www.gnu.org/software/diffutils/
+long_description: |
+  The diff utility is a data comparison tool that calculates and displays the differences between two files. 
+  Unlike edit distance notions used for other purposes, diff is line-oriented rather than character-oriented,
+  but it is like Levenshtein distance in that it tries to determine the smallest set of deletions and insertions
+  to create one file from the other. The diff command displays the changes made in a standard format, such that
+  both humans and machines can understand the changes and apply them: given one file and the changes, the other
+  file can be created.
+name: diff
+owner: bgruening
+remote_repository_url: https://github.com/bgruening/galaxytools/tree/master/tools/diff
+type: unrestricted

tools/diff/diff.xml

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+<tool id="diff" name="diff" version="3.6+galaxy0">
+
+    <description>analyzes two files and generates a text file with information about the lines that are different.</description>
+
+    <stdio>
+        <exit_code range="2:" level="fatal" description="Something went wrong trying to check differences in files. Please check output log for more details." />
+        <regex match="diff: memory exhausted" source="stdout" level="fatal_oom" description="Out of memory error occurred" />
+    </stdio>
+
+    <command ><![CDATA[
+        diff -u '$input1' '$input2' > '$output1'
+    ]]>
+    </command>
+
+    <inputs>
+        <param name="input1" type="data" format="txt" label="First input file" />
+        <param name="input2" type="data" format="txt" label="Second input file" />
+    </inputs>
+
+    <outputs>
+        <data name="output1" format="txt" />
+    </outputs>
+
+    <tests>
+        <test expect_exit_code="0" expect_failure="false">
+            <param name="input1" value="file1.txt" />
+            <param name="input2" value="file1.txt" />
+            <output name="output1">
+                <assert_contents>
+                    <has_n_lines n="0" />
+                </assert_contents>
+            </output>
+        </test>
+        <test expect_exit_code="1" expect_failure="false">
+            <param name="input1" value="file1.txt" />
+            <param name="input2" value="file2.txt" />
+            <output name="output1">
+                <assert_contents>
+                    <has_n_lines n="5" />
+                    <has_line line=" a" />
+                    <has_line line="+b" />
+                </assert_contents>
+            </output>
+        </test>
+    </tests>
+
+    <help><![CDATA[
+.. class:: infomark
+
+**Purpose**
+
+The **diff** utility is a data comparison tool that calculates and displays the differences between two files.
+
+Unlike edit distance notions used for other purposes, diff is line-oriented rather than character-oriented, but it is like Levenshtein distance in that it tries to determine the smallest set of deletions and insertions to create one file from the other.
+
+The diff command displays the changes made in a standard format, such that both humans and machines can understand the changes and apply them: given one file and the changes, the other file can be created.
+
+.. class:: infomark
+
+**Input**
+
+Two text files to be checked for differences line by line.
+
+.. class:: infomark
+
+**Output**
+
+A *single text file*, either:
+
+- containing the lines differences in **unified format** (*unidiff*),
+
+- or an **empty** file if the two input files are the same.
+    ]]>
+    </help>
+
+    <citations>
+        <citation type="bibtex">
+            @misc{gnudiffutils,
+            author = {The Free Software Foundation (FSF), Inc},
+            year = {2017},
+            title = {diff (GNU diffutils)},
+            publisher = {The Free Software Foundation (FSF), Inc},
+            url = {http://www.gnu.org/software/diffutils/},
+            }
+        </citation>
+    </citations>
+</tool>

tools/diff/test-data/file1.txt

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+a

tools/diff/test-data/file2.txt

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+a
+b