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I was reading this post and trying out all of the commands in the first answer... I don't really have anything else better to do right now.

Anyways, I ran through them all in regards to rm. What piqued my interest is this:

root@headdesk:~# type ls
ls is /bin/ls
root@headdesk:~# hash ls
root@headdesk:~# type ls
ls is hashed (/bin/ls)
root@headdesk:~#

Running help/man hash is not very helpful, and help type isn't really either (it does not mention hash anywhere). Since I can't seem to find a relation in the man/info/help pages unless I am missing something, could someone please explain what hashing is doing in regards to the type command?

Community
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cutrightjm
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    your shell remembers where it finds a command. a $PATH search is brute forced otherwise, but if it finds a command it stores its location in a hash table (supposed to be, anyway) so it can call it up next time. if you do PATH=$PATH or hash -r it will forget all executables in the hash table. it doesnt usually affect anything, but it can make a difference for weird lookup tables compiled out of a list of empty files in the current directory, for instance. it used to make things a lot faster, but i dunno if its so true anymore. maybe if $PATH is huge,... – mikeserv Dec 27 '15 at 06:38

2 Answers2

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It means stored in a hash table for quicker reference next time around.

Michael Durrant
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In bash: just type help hash and you will get a help about the built-in command hash.

Determine and remember the full pathname of each command NAME.

What that means is that after finding the location of a command the first time (or when hash is invoked), its location is remembered (hashed).

  • Makes sense - little bit of a different question, but it says obsolete at the bottom of the help page for type. Are there any other commands that you can view if a command is hashed besides type? – cutrightjm Dec 27 '15 at 20:26
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    @ekaj If you do hash cat to get cat hashed, hash -t cat will print the hashed directory. If cat is not hashed hash -d cat, the command hash -t cat will print not found. The Obsolete part apply to the command typeset which happens to also be printed at the end of type in older bash help versions. Does not apply to type. –  Dec 27 '15 at 21:19