[chmod(1)] has a potentially very convenient switch: <tt>-R</tt>, which, as you'll suspect if you've used other [UNIX] tools, means "recurse into directories and apply the change to the entire directory tree." However, because directories need to be executable before you can refer to any of the files inside them, it would sometimes seem that this convenient switch cannot be used. F.ex., saying <tt>chmod -R a-x ./foo/</tt> isn't very useful because that will make everything inside <tt>foo</tt> non-executable, including directories, which means you can't access any of it. 

  

 However, modern [chmod(1)]s understand a special pseudo-permission, called <tt>X</tt> (eg. uppercase X as opposed to <tt>x</tt>). It means "executable, but only when operating on a directory; no change otherwise". That way, you can say <tt>chmod -R a-x,a+X ./foo/</tt>, which will make [chmod(1)] remove the executable bit from every file but then also ''set'' the executable bit if it's a directory. 

  

  

 !!! See also 

  

 * [An excellent guide to permissions at Greg's wiki | http://wooledge.org/mywiki/Permissions] 

 * [A Linux Focus article about file permissions | http://www.linuxfocus.org/English/January1999/article77.html] 

  

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