On Fri, Nov 11, 2011 at 03:31:02PM -0700, Eric Blake wrote: > On 11/11/2011 03:23 PM, Peng Yu wrote: > > I'm not aware if there is any cache mechanism > > to save the run time (but even so, different terminals still can not > > see the same cache, hence each terminal has the overhead to create the > > cache).
Bash *does* cache paths. imadev:~$ type comm comm is /usr/bin/comm imadev:~$ comm -? comm: illegal option -- ? usage: comm [ -[123] ] file1 file2 imadev:~$ type comm comm is hashed (/usr/bin/comm) > > When there are many files in PATH, it is going to slow down > > the performance. You mean directories? Then put the most popular directories first. > Bash isn't doing the resolution so much as libc (read 'man execvp') > (well, technically, bash may be manually repeating some of the same > resolution code as in execvp for other reasons, but the same principles > apply). Bash does indeed perform the PATH lookup itself in order to cache the results. > If you want to search fewer directories, then nothing is stopping you from: > > mkdir ~/mycache > for every executable you want cached: > ln -s executable ~/mycache/ > PATH=$HOME/mycache:$PATH > Meanwhile, per POSIX, bash DOES provide hashing once it learns where an > executable lives, so that future invocations can rely on the hash (the > hash is invalidated when you assign to $PATH). Read up on 'help hash'.
