Difference between revisions of "Diff"

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=General description of diff=
 
'''diff''' is a command line utility that compares two sources (usually files) and displays the differences. In CS courses context, '''diff''' is often used to compare the output the student program with the output of the school solution, both provided with the same input, for debugging purposes.
 
'''diff''' is a command line utility that compares two sources (usually files) and displays the differences. In CS courses context, '''diff''' is often used to compare the output the student program with the output of the school solution, both provided with the same input, for debugging purposes.
  
===Using md5sum as a diff replacement===
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==usage==
md5sum is a common shell utility that gives the md5-hash of a file. Skipping some interesting details, files with the same hash code are completely identical. Since comparing large files stored in different computers is slightly impractical due to the time needed to transfer the files, '''md5sum''' is often used to create a md5-hash of a file in each computer, than comparing them. This technique
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  '''echo "Labaneh" > a'''
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  '''echo "Labaneh" > b'''
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  '''diff a b''' // No output - files are identical.
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  '''rm a'''
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  '''echo "labaneh" > a''' // Note the difference
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  '''diff a b'''
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  1c1
 +
  < labaneh
 +
  ---
 +
  > Labaneh
  
===External Links===
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=diff frontends and variants=
 +
==diff frontends==
 +
'''diff''' has some GUI frontends. The frontends are most useful trying to understand the specific whereabouts and nature of a textual '''diff''' output the yielded differences; The differences are nicely highlighted for the user, including whitespaces. Common frontends are tkdiff and xxdiff.
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 +
==diff-ing 3 files==
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'''diff3''' is used for comparing 3 files.
 +
 
 +
=Using md5sum as a diff replacement=
 +
md5sum is a common shell utility that gives the md5-hash of a file. Skipping some interesting details, files with the same hash code are completely identical. Since comparing large files stored in different computers is slightly impractical due to the time needed to transfer the files, '''md5sum''' is often used to create a md5-hash of a file in each computer, than comparing them. This technique is also used to assure that files are identical to the bit, as '''diff''' may be configured to skip white spaces.
 +
 
 +
==usage==
 +
Creating a file, checking its md5sum:
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  $ '''echo "Labaneh" > a'''
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  $ '''md5sum a'''
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  b83c24f2d3cf387845cb7fde205a3a87 *a
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  $ '''echo "Labaneh" > b'''
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  $ '''md5sum b'''
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  b83c24f2d3cf387845cb7fde205a3a87 *b
 +
 
 +
Checking the md5 has of two files:
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  $ '''md5sum a b'''
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  b83c24f2d3cf387845cb7fde205a3a87 *a
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  b83c24f2d3cf387845cb7fde205a3a87 *b  // Identical hash codes, Identical files
 +
 
 +
Applying changes to the files:
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  $ '''echo "Humus" >> a'''
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  $ '''cat a'''
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  Labaneh
 +
  Humus
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  '''$ md5sum a b'''
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  3763552bf8bd868dec3e321ecc7886ea *a
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  b83c24f2d3cf387845cb7fde205a3a87 *b  // Note the difference!
 +
  $ '''echo "Humus" >> b'''
 +
  $ '''md5sum a b'''
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  3763552bf8bd868dec3e321ecc7886ea *a
 +
  3763552bf8bd868dec3e321ecc7886ea *b  // Once again, identical.
 +
 
 +
 
 +
=External Links=
  
 
[http://en.wikipedia.org/wiki/Diff Wikipedia's '''diff''' page]
 
[http://en.wikipedia.org/wiki/Diff Wikipedia's '''diff''' page]

Revision as of 17:04, 30 November 2006

General description of diff

diff is a command line utility that compares two sources (usually files) and displays the differences. In CS courses context, diff is often used to compare the output the student program with the output of the school solution, both provided with the same input, for debugging purposes.

usage

 echo "Labaneh" > a
 echo "Labaneh" > b
 diff a b // No output - files are identical.
 rm a
 echo "labaneh" > a // Note the difference
 diff a b
 1c1
 < labaneh
 ---
 > Labaneh

diff frontends and variants

diff frontends

diff has some GUI frontends. The frontends are most useful trying to understand the specific whereabouts and nature of a textual diff output the yielded differences; The differences are nicely highlighted for the user, including whitespaces. Common frontends are tkdiff and xxdiff.

diff-ing 3 files

diff3 is used for comparing 3 files.

Using md5sum as a diff replacement

md5sum is a common shell utility that gives the md5-hash of a file. Skipping some interesting details, files with the same hash code are completely identical. Since comparing large files stored in different computers is slightly impractical due to the time needed to transfer the files, md5sum is often used to create a md5-hash of a file in each computer, than comparing them. This technique is also used to assure that files are identical to the bit, as diff may be configured to skip white spaces.

usage

Creating a file, checking its md5sum:

 $ echo "Labaneh" > a
 $ md5sum a
 b83c24f2d3cf387845cb7fde205a3a87 *a
 $ echo "Labaneh" > b
 $ md5sum b
 b83c24f2d3cf387845cb7fde205a3a87 *b

Checking the md5 has of two files:

 $ md5sum a b
 b83c24f2d3cf387845cb7fde205a3a87 *a
 b83c24f2d3cf387845cb7fde205a3a87 *b  // Identical hash codes, Identical files

Applying changes to the files:

 $ echo "Humus" >> a
 $ cat a
 Labaneh
 Humus
 $ md5sum a b
 3763552bf8bd868dec3e321ecc7886ea *a
 b83c24f2d3cf387845cb7fde205a3a87 *b  // Note the difference!
 $ echo "Humus" >> b
 $ md5sum a b
 3763552bf8bd868dec3e321ecc7886ea *a
 3763552bf8bd868dec3e321ecc7886ea *b  // Once again, identical.


External Links

Wikipedia's diff page