I am aware of the bash internal command hash and how one can use hash -d or hash -r to forget remembered locations. Is there a way to instruct bash to automatically do this whenever it gets a "cache miss", i.e. when the remembered location goes away (no such file or directory) bash would clear the remembered location and try again?


You can achieve this with the checkhash option:

shopt -s checkhash

    If set, bash checks that a command found in the hash table exists
    before trying to execute it.  If  a  hashed  command  no longer
    exists, a normal path search is performed.

You can make that the option for all bash shells by putting it into the BASHOPTS environment variable:

    A colon-separated list of enabled shell options.
    Each word in the list is a valid argument for the
    -s option to the shopt builtin command.

Setting this option may slightly slow down bash execution, since almost all of the time, the extra test is unnecessary. However, I wouldn't think that the cost of the test is significant.

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    The cost of the test is relevant (each disk access == latency), but you are comparing that cost to the cost of searching the entire PATH for the file. Seems cheap for providing the feature the requester wanted. – Slartibartfast Mar 27 '14 at 5:55
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    @slartibartfast: agreed. As I said, the cost is probably not significant. – rici Mar 27 '14 at 6:10
  • Thanks, this is exactly what I wanted. I wonder if there are Linux dists with this option set as the default? – Gerry Lufwansa Mar 27 '14 at 6:17
  • @GerryLufwansa: I doubt it, but it hardly seems like a deciding feature for a selecting a distro. It's just one line to add to your bash startup file (although figuring out which file can be a challenge with some distributions). – rici Mar 27 '14 at 18:50

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