Macでのwhereisコマンドとwhichコマンドの違い

Mac

whereisもwhichも、どちらもコマンドのパスを調べるコマンドです。
MacPortsで入れたコマンドに対してwhereisしても、なぜか反応がなく、不思議だったので調べてみました。

結論

whereisは/usr/bin:/bin:/usr/sbin:/sbinにあるコマンドのみ調べられる。
whichは環境変数のPATHにあるコマンドから調べられる。
通常はwhichを主に使ったほうが良いみたい。

whereisコマンド

$ man whereis

WHEREIS(1)                BSD General Commands Manual               WHEREIS(1)

NAME
     whereis -- locate programs

SYNOPSIS
     whereis [program ...]

DESCRIPTION
     The whereis utility checks the standard binary directories for the specified programs, printing out the paths of any it finds.

     The path searched is the string returned by the sysctl(8) utility for the ``user.cs_path'' string.

SEE ALSO
     sysctl(8)

COMPATIBILITY
     The historic flags and arguments for the whereis utility are no longer available in this version.

HISTORY
     The whereis command appeared in 3.0BSD.

3rd Berkeley Distribution       April 27, 1995       3rd Berkeley Distribution

The path searched is the string returned by the sysctl(8) utility for the ``user.cs_path'' string.

whereisコマンドのmanページを見ると、こんな一文があります。

$ sysctl user.cs_path
user.cs_path = /usr/bin:/bin:/usr/sbin:/sbin

実際にsysctlを使ってみると、こんなパスが出てきます。
どうやら、whereisコマンドは'checks the standard binary directories'という事のようです。

名称
sysctl - カーネル状態の取得や設定

http://www.jp.freebsd.org/cgi/mroff.cgi?subdir=man&lc=1&cmd=&man=sysctl&dir=jpman-5.4.0%2Fman§=0

ちなみに、sysctlコマンドはこういうものらしい。

whichコマンド

$ man which

WHICH(1)                  BSD General Commands Manual                 WHICH(1)

NAME
     which -- locate a program file in the user's path

SYNOPSIS
     which [-as] program ...

DESCRIPTION
     The which utility takes a list of command names and searches the path for each executable file that would be run had these commands actually been invoked.

     The following options are available:

     -a      List all instances of executables found (instead of just the first one of each).

     -s      No output, just return 0 if any of the executables are found, or 1 if none are found.

     Some shells may provide a builtin which command which is similar or identical to this utility.  Consult the builtin(1) manual page.

SEE ALSO
     builtin(1), csh(1), find(1), locate(1), whereis(1)

HISTORY
     The which command first appeared in FreeBSD 2.1.

AUTHORS
     The which utility was originally written in Perl and was contributed by Wolfram Schneider <wosch@FreeBSD.org>.  The current version of which was rewritten in C by Daniel Papasian
     <dpapasia@andrew.cmu.edu>.

BSD                              June 21, 2002                             BSD

locate a program file in the user's path

この一文から、PATHを見てコマンドのパスを調べてくれることが伺えます。
実際にMacPortsで入れたコマンドのパスも調べられました。