What effect does the -d/--minimal option have with diff?

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The diff implementation on OpenBSD has a non-standard -d option with the following documentation:




-d



Try very hard to produce a diff as small as possible. This may
consume a lot of processing power and memory when processing
large files with many changes.




The GNU diff implementation has the same option with the shorter documentation




-d, --minimal



try hard to find a smaller set of changes




From time to time I've used this option just to see if it generates output that is in any shape or form different from the same diff command without the option, but I've never seen any difference (no pun intended).



Could someone provide or point to an example where this option actually produces a different result from the same command without -d? Alternatively, if someone could explain the circumstances required for this option to kick in. I'm also uncertain whether "minimal" means "fewer lines of output" or "fewer hunks".



An uneducated guess is that it has to do with very large hunks.






diff







share|improve this question























  • unix.stackexchange.com/questions/472528 piqued your curiosity did it? (-:
    – JdeBP
    18 hours ago










  • @JdeBP Yes indeed. It reminded me about this flag and the fact that I simply don't know what it does since I've never seen it do anything.
    – Kusalananda
    18 hours ago






  • 1




    info diff performance explains it IIRC
    – Stéphane Chazelas
    18 hours ago














up vote
19
down vote

favorite
1












The diff implementation on OpenBSD has a non-standard -d option with the following documentation:




-d



Try very hard to produce a diff as small as possible. This may
consume a lot of processing power and memory when processing
large files with many changes.




The GNU diff implementation has the same option with the shorter documentation




-d, --minimal



try hard to find a smaller set of changes




From time to time I've used this option just to see if it generates output that is in any shape or form different from the same diff command without the option, but I've never seen any difference (no pun intended).



Could someone provide or point to an example where this option actually produces a different result from the same command without -d? Alternatively, if someone could explain the circumstances required for this option to kick in. I'm also uncertain whether "minimal" means "fewer lines of output" or "fewer hunks".



An uneducated guess is that it has to do with very large hunks.






diff







share|improve this question























  • unix.stackexchange.com/questions/472528 piqued your curiosity did it? (-:
    – JdeBP
    18 hours ago










  • @JdeBP Yes indeed. It reminded me about this flag and the fact that I simply don't know what it does since I've never seen it do anything.
    – Kusalananda
    18 hours ago






  • 1




    info diff performance explains it IIRC
    – Stéphane Chazelas
    18 hours ago












up vote
19
down vote

favorite
1









up vote
19
down vote

favorite
1






1





The diff implementation on OpenBSD has a non-standard -d option with the following documentation:




-d



Try very hard to produce a diff as small as possible. This may
consume a lot of processing power and memory when processing
large files with many changes.




The GNU diff implementation has the same option with the shorter documentation




-d, --minimal



try hard to find a smaller set of changes




From time to time I've used this option just to see if it generates output that is in any shape or form different from the same diff command without the option, but I've never seen any difference (no pun intended).



Could someone provide or point to an example where this option actually produces a different result from the same command without -d? Alternatively, if someone could explain the circumstances required for this option to kick in. I'm also uncertain whether "minimal" means "fewer lines of output" or "fewer hunks".



An uneducated guess is that it has to do with very large hunks.






diff







share|improve this question















The diff implementation on OpenBSD has a non-standard -d option with the following documentation:




-d



Try very hard to produce a diff as small as possible. This may
consume a lot of processing power and memory when processing
large files with many changes.




The GNU diff implementation has the same option with the shorter documentation




-d, --minimal



try hard to find a smaller set of changes




From time to time I've used this option just to see if it generates output that is in any shape or form different from the same diff command without the option, but I've never seen any difference (no pun intended).



Could someone provide or point to an example where this option actually produces a different result from the same command without -d? Alternatively, if someone could explain the circumstances required for this option to kick in. I'm also uncertain whether "minimal" means "fewer lines of output" or "fewer hunks".



An uneducated guess is that it has to do with very large hunks.






diff




diff






share|improve this question















share|improve this question













share|improve this question




share|improve this question








edited 4 mins ago









muru

33.8k577146




33.8k577146










asked 19 hours ago









Kusalananda

108k14209332




108k14209332











  • unix.stackexchange.com/questions/472528 piqued your curiosity did it? (-:
    – JdeBP
    18 hours ago










  • @JdeBP Yes indeed. It reminded me about this flag and the fact that I simply don't know what it does since I've never seen it do anything.
    – Kusalananda
    18 hours ago






  • 1




    info diff performance explains it IIRC
    – Stéphane Chazelas
    18 hours ago
















  • unix.stackexchange.com/questions/472528 piqued your curiosity did it? (-:
    – JdeBP
    18 hours ago










  • @JdeBP Yes indeed. It reminded me about this flag and the fact that I simply don't know what it does since I've never seen it do anything.
    – Kusalananda
    18 hours ago






  • 1




    info diff performance explains it IIRC
    – Stéphane Chazelas
    18 hours ago















unix.stackexchange.com/questions/472528 piqued your curiosity did it? (-:
– JdeBP
18 hours ago




unix.stackexchange.com/questions/472528 piqued your curiosity did it? (-:
– JdeBP
18 hours ago












@JdeBP Yes indeed. It reminded me about this flag and the fact that I simply don't know what it does since I've never seen it do anything.
– Kusalananda
18 hours ago




@JdeBP Yes indeed. It reminded me about this flag and the fact that I simply don't know what it does since I've never seen it do anything.
– Kusalananda
18 hours ago




1




1




info diff performance explains it IIRC
– Stéphane Chazelas
18 hours ago




info diff performance explains it IIRC
– Stéphane Chazelas
18 hours ago










1 Answer
1






active

oldest

votes

















up vote
12
down vote



accepted










In GNU diff, also used on FreeBSD, the --minimal flag triggers an algorithm variation by Paul Eggert that causes it "to limit the cost to O(N**1.5 log N) at the price of producing suboptimal output for large inputs with differences". More specifically, it causes it to not apply several heuristics that deal in finding merely close to optimal solutions and in throwing out "confusing" lines as extra differences.



In OpenBSD diff, which uses the older Unix diff algorithm from the 1970s, the algorithm employed is credited to Harold Stone, and the --minimal flag triggers a search that is (effectively un-) bounded by the maximum value of an unsigned integer instead of by the square root of the size of the range of lines being compared (or 256 if it is greater).



Further reading



  • Eugene W. Myers (November 1986). "An O(ND) difference algorithm and its variations". Algorithmica. Volume 1. Issue 1–4. pp. 251–266. DOI 10.1007/BF01840446.

  • J. W. Hunt and M. D. McIlroy (June 1976). "An Algorithm for Differential File Comparison". Report 41. Computing Science. Bell Laboratories.

  • Richard Hartman (1988-01-13). Unix diff(1) algorithm.
    23225@cca.CCA.COM. comp.unix.questions.

  • https://github.com/openbsd/src/blob/d1e24f318523607c98dc6fbe5a06a5d9e5c87293/usr.bin/diff/diffreg.c#L93

  • https://github.com/freebsd/freebsd/blob/40ec4fdc9a74bfdb83f13672acdb88af5c91ab46/contrib/diff/src/analyze.c#L23

  • Comprehensive review of diff algorithms, their history and implementations





share|improve this answer






















  • When I created a better diff from the UNIX sources, I checked that OpenBSD enhancement and could not find any better results. Note that the original stone() function uses: ` } while ((y = b[++j]) > 0);` and BTW: for normal file sizes, my enhanced UNIX diff is faster than GNU diff.
    – schily
    17 hours ago










  • Thanks for the references!
    – Kusalananda
    13 hours ago










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1 Answer
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active

oldest

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1 Answer
1






active

oldest

votes









active

oldest

votes






active

oldest

votes








up vote
12
down vote



accepted










In GNU diff, also used on FreeBSD, the --minimal flag triggers an algorithm variation by Paul Eggert that causes it "to limit the cost to O(N**1.5 log N) at the price of producing suboptimal output for large inputs with differences". More specifically, it causes it to not apply several heuristics that deal in finding merely close to optimal solutions and in throwing out "confusing" lines as extra differences.



In OpenBSD diff, which uses the older Unix diff algorithm from the 1970s, the algorithm employed is credited to Harold Stone, and the --minimal flag triggers a search that is (effectively un-) bounded by the maximum value of an unsigned integer instead of by the square root of the size of the range of lines being compared (or 256 if it is greater).



Further reading



  • Eugene W. Myers (November 1986). "An O(ND) difference algorithm and its variations". Algorithmica. Volume 1. Issue 1–4. pp. 251–266. DOI 10.1007/BF01840446.

  • J. W. Hunt and M. D. McIlroy (June 1976). "An Algorithm for Differential File Comparison". Report 41. Computing Science. Bell Laboratories.

  • Richard Hartman (1988-01-13). Unix diff(1) algorithm.
    23225@cca.CCA.COM. comp.unix.questions.

  • https://github.com/openbsd/src/blob/d1e24f318523607c98dc6fbe5a06a5d9e5c87293/usr.bin/diff/diffreg.c#L93

  • https://github.com/freebsd/freebsd/blob/40ec4fdc9a74bfdb83f13672acdb88af5c91ab46/contrib/diff/src/analyze.c#L23

  • Comprehensive review of diff algorithms, their history and implementations





share|improve this answer






















  • When I created a better diff from the UNIX sources, I checked that OpenBSD enhancement and could not find any better results. Note that the original stone() function uses: ` } while ((y = b[++j]) > 0);` and BTW: for normal file sizes, my enhanced UNIX diff is faster than GNU diff.
    – schily
    17 hours ago










  • Thanks for the references!
    – Kusalananda
    13 hours ago














up vote
12
down vote



accepted










In GNU diff, also used on FreeBSD, the --minimal flag triggers an algorithm variation by Paul Eggert that causes it "to limit the cost to O(N**1.5 log N) at the price of producing suboptimal output for large inputs with differences". More specifically, it causes it to not apply several heuristics that deal in finding merely close to optimal solutions and in throwing out "confusing" lines as extra differences.



In OpenBSD diff, which uses the older Unix diff algorithm from the 1970s, the algorithm employed is credited to Harold Stone, and the --minimal flag triggers a search that is (effectively un-) bounded by the maximum value of an unsigned integer instead of by the square root of the size of the range of lines being compared (or 256 if it is greater).



Further reading



  • Eugene W. Myers (November 1986). "An O(ND) difference algorithm and its variations". Algorithmica. Volume 1. Issue 1–4. pp. 251–266. DOI 10.1007/BF01840446.

  • J. W. Hunt and M. D. McIlroy (June 1976). "An Algorithm for Differential File Comparison". Report 41. Computing Science. Bell Laboratories.

  • Richard Hartman (1988-01-13). Unix diff(1) algorithm.
    23225@cca.CCA.COM. comp.unix.questions.

  • https://github.com/openbsd/src/blob/d1e24f318523607c98dc6fbe5a06a5d9e5c87293/usr.bin/diff/diffreg.c#L93

  • https://github.com/freebsd/freebsd/blob/40ec4fdc9a74bfdb83f13672acdb88af5c91ab46/contrib/diff/src/analyze.c#L23

  • Comprehensive review of diff algorithms, their history and implementations





share|improve this answer






















  • When I created a better diff from the UNIX sources, I checked that OpenBSD enhancement and could not find any better results. Note that the original stone() function uses: ` } while ((y = b[++j]) > 0);` and BTW: for normal file sizes, my enhanced UNIX diff is faster than GNU diff.
    – schily
    17 hours ago










  • Thanks for the references!
    – Kusalananda
    13 hours ago












up vote
12
down vote



accepted







up vote
12
down vote



accepted






In GNU diff, also used on FreeBSD, the --minimal flag triggers an algorithm variation by Paul Eggert that causes it "to limit the cost to O(N**1.5 log N) at the price of producing suboptimal output for large inputs with differences". More specifically, it causes it to not apply several heuristics that deal in finding merely close to optimal solutions and in throwing out "confusing" lines as extra differences.



In OpenBSD diff, which uses the older Unix diff algorithm from the 1970s, the algorithm employed is credited to Harold Stone, and the --minimal flag triggers a search that is (effectively un-) bounded by the maximum value of an unsigned integer instead of by the square root of the size of the range of lines being compared (or 256 if it is greater).



Further reading



  • Eugene W. Myers (November 1986). "An O(ND) difference algorithm and its variations". Algorithmica. Volume 1. Issue 1–4. pp. 251–266. DOI 10.1007/BF01840446.

  • J. W. Hunt and M. D. McIlroy (June 1976). "An Algorithm for Differential File Comparison". Report 41. Computing Science. Bell Laboratories.

  • Richard Hartman (1988-01-13). Unix diff(1) algorithm.
    23225@cca.CCA.COM. comp.unix.questions.

  • https://github.com/openbsd/src/blob/d1e24f318523607c98dc6fbe5a06a5d9e5c87293/usr.bin/diff/diffreg.c#L93

  • https://github.com/freebsd/freebsd/blob/40ec4fdc9a74bfdb83f13672acdb88af5c91ab46/contrib/diff/src/analyze.c#L23

  • Comprehensive review of diff algorithms, their history and implementations





share|improve this answer














In GNU diff, also used on FreeBSD, the --minimal flag triggers an algorithm variation by Paul Eggert that causes it "to limit the cost to O(N**1.5 log N) at the price of producing suboptimal output for large inputs with differences". More specifically, it causes it to not apply several heuristics that deal in finding merely close to optimal solutions and in throwing out "confusing" lines as extra differences.



In OpenBSD diff, which uses the older Unix diff algorithm from the 1970s, the algorithm employed is credited to Harold Stone, and the --minimal flag triggers a search that is (effectively un-) bounded by the maximum value of an unsigned integer instead of by the square root of the size of the range of lines being compared (or 256 if it is greater).



Further reading



  • Eugene W. Myers (November 1986). "An O(ND) difference algorithm and its variations". Algorithmica. Volume 1. Issue 1–4. pp. 251–266. DOI 10.1007/BF01840446.

  • J. W. Hunt and M. D. McIlroy (June 1976). "An Algorithm for Differential File Comparison". Report 41. Computing Science. Bell Laboratories.

  • Richard Hartman (1988-01-13). Unix diff(1) algorithm.
    23225@cca.CCA.COM. comp.unix.questions.

  • https://github.com/openbsd/src/blob/d1e24f318523607c98dc6fbe5a06a5d9e5c87293/usr.bin/diff/diffreg.c#L93

  • https://github.com/freebsd/freebsd/blob/40ec4fdc9a74bfdb83f13672acdb88af5c91ab46/contrib/diff/src/analyze.c#L23

  • Comprehensive review of diff algorithms, their history and implementations






share|improve this answer














share|improve this answer



share|improve this answer








edited 9 hours ago









bishop

1,7932719




1,7932719










answered 17 hours ago









JdeBP

29.9k462137




29.9k462137











  • When I created a better diff from the UNIX sources, I checked that OpenBSD enhancement and could not find any better results. Note that the original stone() function uses: ` } while ((y = b[++j]) > 0);` and BTW: for normal file sizes, my enhanced UNIX diff is faster than GNU diff.
    – schily
    17 hours ago










  • Thanks for the references!
    – Kusalananda
    13 hours ago
















  • When I created a better diff from the UNIX sources, I checked that OpenBSD enhancement and could not find any better results. Note that the original stone() function uses: ` } while ((y = b[++j]) > 0);` and BTW: for normal file sizes, my enhanced UNIX diff is faster than GNU diff.
    – schily
    17 hours ago










  • Thanks for the references!
    – Kusalananda
    13 hours ago















When I created a better diff from the UNIX sources, I checked that OpenBSD enhancement and could not find any better results. Note that the original stone() function uses: ` } while ((y = b[++j]) > 0);` and BTW: for normal file sizes, my enhanced UNIX diff is faster than GNU diff.
– schily
17 hours ago




When I created a better diff from the UNIX sources, I checked that OpenBSD enhancement and could not find any better results. Note that the original stone() function uses: ` } while ((y = b[++j]) > 0);` and BTW: for normal file sizes, my enhanced UNIX diff is faster than GNU diff.
– schily
17 hours ago












Thanks for the references!
– Kusalananda
13 hours ago




Thanks for the references!
– Kusalananda
13 hours ago

















 

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