_chapter 13.htm

linux、unix初学者的必读书籍 详细讲述了shell编程方法与技巧

2      setenv PATH "${PATH}:/usr/X11R6/bin"
   else
3       setenv PATH "/bin:/usr/bin:/usr/local/bin:/usr/X11R6/bin"
   endif

4  if ($?prompt) then
5       [ "$SHELL" = /bin/tcsh ]
6       if  ($status == 0) then
7            set prompt='[%n@%m %c]$ '
8       else
9            set prompt=\['id -nu'@'hostname -s'\]\$\
10      endif
   endif
11 limit coredumpsize 1000000

12  [ 'id -gn' = 'id -un' -a 'id -u' -gt 14 ]
13  if $status then
14      umask 022
    else
15      umask 002
    endif

16  setenv HOSTNAME '/bin/hostname'
17  set history=1000

18  test -d /etc/profile.d
19    if ($status == 0) then
20      set nonomatch
21        foreach i ( /etc/profile.d/*.csh )
22           test -f $i
             if ($status == 0) then
23                    source $i
             endif
        end
24     unset nonomatch
      endif</pre>
<table cellSpacing="0" width="90%" border="1" align="center">
  <tr>
    <td>
    <h2 class="docSidebarTitle">EXPLANATION</h2>
    <span style="font-weight: bold">
    <ol class="docList" type="1">
      <li><span style="font-weight: normal">
      <p class="docList"><span class="docEmphasis">$?PATH</span> is a test to
      see if the <span class="docEmphasis">PATH</span> variable has been set; it
      returns <span class="docEmphasis">1</span> if true.</span></li>
      <li><span style="font-weight: normal">
      <p class="docList">If the <span class="docEmphasis">PATH</span> variable
      has been set, <span class="docEmphasis">/usr/X11R6/bin</span> is appended
      to it. This is a directory that contains the <span class="docEmphasis">X</span>
      windows files.</span></li>
      <li><span style="font-weight: normal">
      <p class="docList">If the <span class="docEmphasis">PATH</span> variable
      has not been previously set, this line sets it to
      <span class="docEmphasis">/bin:/usr/bin:/usr/local/bin:/usr/X11R6/bin</span></span></li>
      <li><span style="font-weight: normal">
      <p class="docList">This line checks to see if the prompt has been set.</span></li>
      <li><span style="font-weight: normal">
      <p class="docList">When you place the expression in square brackets, the
      expression will be tested and if the result of the expression is true, a
      zero exit status is returned; otherwise a nonzero exit status is returned.
      If the value of the <span class="docEmphasis">SHELL</span> environment
      variable is <span class="docEmphasis">/bin/tcsh,</span> the exit status
      will be <span class="docEmphasis">0.</span></span></li>
      <li><span style="font-weight: normal">
      <p class="docList">The <span class="docEmphasis">status</span> variable
      contains the exit status of the last command executed, which in this
      example, is the previous test on line 5.</span></li>
      <li><span style="font-weight: normal">
      <p class="docList">If the status from the last command was zero, the
      prompt for the <span class="docEmphasis">/bin/tcsh</span> is set. The
      prompt will be set to the user's name followed by an @ symbol, the
      hostname, and the current working directory (all enclosed in
      <span class="docEmphasis">[ ]</span> ), followed by a dollar sign; e.g.,
      <span class="docEmphasis">[ ellie@homebound ~ ]$</span></span></li>
      <li><span style="font-weight: normal">
      <p class="docList">If the status was nonzero, the
      <span class="docEmphasis">else</span> branches program control to line 9.</span></li>
      <li><span style="font-weight: normal">
      <p class="docList">This line sets the prompt for the standard
      <span class="docEmphasis">csh</span> program. It will print the user's
      name (<span class="docEmphasis">id -un</span>), an
      <span class="docEmphasis">@</span> symbol, and the short name for his host
      machine, i.e., the hostname cut at the first dot, and a
      <span class="docEmphasis">$.</span></span></li>
      <li><span style="font-weight: normal">
      <p class="docList">The <span class="docEmphasis">endif</span> terminates
      the inner <span class="docEmphasis">if</span> block.</span></li>
      <li><span style="font-weight: normal">
      <p class="docList">The size of core files (usually created when a program
      crashes for some illegal system operation) is limited to 1,000,000 bytes.
      Core files are created if you abort a running program with Control-\.</span></li>
      <li><span style="font-weight: normal">
      <p class="docList">If the group ID number and the user ID number are the
      same, and the user ID number is greater than 14, then the next line will
      be executed; otherwise, the line under the <span class="docEmphasis">else</span>
      will be executed. Typically, user IDs below 14 are for special users, such
      as <span class="docEmphasis">root, daemon, adm,</span>
      <span class="docEmphasis">lp,</span> etc. (See <span class="docEmphasis">
      /etc/passwd.</span> The user ID is in field number 3.)</span></li>
      <li><span style="font-weight: normal">
      <p class="docList">If the test in the previous line returned a nonzero
      exit status, line 14 is executed, else line 15 is executed.</span></li>
      <li><span style="font-weight: normal">
      <p class="docList">The <span class="docEmphasis">umask</span> command sets
      the file creation mask; i.e., the initial permissions for files and
      directories when created. Directories will get <span class="docEmphasis">
      755</span> (<span class="docEmphasis">rwxr-xr-x</span>) and files will get
      <span class="docEmphasis">644</span> (<span class="docEmphasis">rw-r--r--</span>)
      when they are created.</span></li>
      <li><span style="font-weight: normal">
      <p class="docList"><span class="docEmphasis">Umask</span> is set so that
      when a directory is created, its permissions will be
      <span class="docEmphasis">775</span> (<span class="docEmphasis">rwxrwxr-x</span>)
      and files will get <span class="docEmphasis">664</span> (<span class="docEmphasis">rw-rw-r--</span>).
      </span></li>
      <li><span style="font-weight: normal">
      <p class="docList">The environment variable <span class="docEmphasis">
      HOSTNAME</span> is assigned the output of the <span class="docEmphasis">
      /bin/hostname</span> command.</span></li>
      <li><span style="font-weight: normal">
      <p class="docList">The <span class="docEmphasis">history</span> variable
      is set to <span class="docEmphasis">1000.</span> When commands are typed
      at the command line, they are saved in a history list. When you set the
      history variable to <span class="docEmphasis">1000,</span> no more than
      1,000 commands will be displayed when the <span class="docEmphasis">
      history</span> command is typed.</span></li>
      <li><span style="font-weight: normal">
      <p class="docList">The <span class="docEmphasis">test</span> command
      returns zero exit status if the <span class="docEmphasis">/etc/profile.d</span>
      directory exists, and nonzero if it doesn't.</span></li>
      <li><span style="font-weight: normal">
      <p class="docList">If the status is <span class="docEmphasis">0,</span>
      the directory exists, and the program branches to line 20.</span></li>
      <li><span style="font-weight: normal">
      <p class="docList">The <span class="docEmphasis">nonomatch</span> variable
      is set to prevent the shell from sending an error message if any of its
      special metacharacters (<span class="docEmphasis">*,</span>
      <span class="docEmphasis">?,</span> <span class="docEmphasis">[]</span>)
      cannot be matched.</span></li>
      <li><span style="font-weight: normal">
      <p class="docList">The <span class="docEmphasis">foreach</span> loop
      assigns each file with a <span class="docEmphasis">.csh</span> extension (<span class="docEmphasis">*.csh</span>)
      in the <span class="docEmphasis">/etc/profile.d</span> directory to the
      variable <span class="docEmphasis">i,</span> in turn, looping until each
      file has been tested (lines 22