Why are my command line utilities running so slowly on my Mac?

I have just noticed that command line utilities such as ls (/bin/ls), touch (/usr/bin/touch), cat (/bin/cat), etc. are very slow when I run them from Terminal or iTerm on my MacBook. For example:

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  ls'ing while in an empty directory takes 1 second (it also takes 1 second in a non-empty directory, both with lots of files or with a few files);

  
  


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  touch'ing a new file takes 1 second (it also takes 1 second to touch an existing file);

  
  


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  cat'ing an empty file takes 1 second (there is also a 1 second lag before anything happens when I cat a non-empty file).

  
  

I have tried to diagnose this in many ways but to no avail. I do not think this is a filesystem issue, since:

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  I have run Disk Utility and it reports no problems.

  
  


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  Everything seems to be working just fine in Finder, e.g. directory contents are shown instantaneously in Finder.

  
  


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  I installed GNU coreutils using Homebrew and tried using gls, gtouch, gcat, etc., and all of the operations I listed above happen instantaneously when run with the GNU version instead.

  
  

Any ideas on what could be going on? Any ideas on how to fix this?

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EDIT: When I reboot the computer, or try a different user, these issues go away temporarily, but after a few minutes they seem to reappear again. Another strange thing that I noticed:

$ time date
Wed Jan 28 10:07:11 PST 2015

real    0m0.151s
user    0m0.001s
sys     0m0.003s

$ time date
Wed Jan 28 10:07:13 PST 2015

real    0m0.029s
user    0m0.001s
sys     0m0.002s

$ time date
Wed Jan 28 10:07:16 PST 2015

real    0m1.005s
user    0m0.001s
sys     0m0.002s

$ time date
Wed Jan 28 10:07:18 PST 2015

real    0m1.005s
user    0m0.001s
sys     0m0.002s

This happens for all the utilities I've tried, mkdir, scp, sftp, more, cat, etc.: The first time I run it after a reboot, it's medium-slow. The second time I run it, it's sorta-fast. All subsequent times I run it, it's slow.