100 CoolShell ch01 問(wèn)題

yanjerry9133

1. #!/bin/sh
   
2. # inpath - Verifies that a specified program is either valid as is,
   
3. #   or that it can be found in the PATH directory list.
   
4. 
   
5. in_path()
   
6. {
   
7.   # Given a command and the PATH, try to find the command. Returns
   
8.   # 0 if found and executable, 1 if not. Note that this temporarily modifies
   
9.   # the IFS (input field separator) but restores it upon completion.
   
10. 
    
11.   cmd=$1        path=$2         retval=1
    
12.   oldIFS=$IFS   IFS=":"
    
13. 
    
14.   for directory in $path
    
15.   do
    
16.     if [ -x $directory/$cmd ] ; then
    
17.       retval=0      # if we're here, we found $cmd in $directory
    
18.     fi
    
19.   done
    
20.   IFS=$oldIFS
    
21.   return $retval
    
22. }
    
23. 
    
24. checkForCmdInPath()
    
25. {
    
26.   var=$1
    
27. 
    
28.   # The variable slicing notation in the following conditional
    
29.   # needs some explanation: ${var#expr} returns everything after
    
30.   # the match for 'expr' in the variable value (if any), and
    
31.   # ${var%expr} returns everything that doesn't match (in this
    
32.   # case, just the very first character. You can also do this in
    
33.   # Bash with ${var:0:1}, and you could use cut too: cut -c1.
    
34. 
    
35.   if [ "$var" != "" ] ; then
    
36.     if [ "${var%${var#?}}" = "/" ] ; then
    
37.       if [ ! -x $var ] ; then
    
38.         return 1
    
39.       fi
    
40.     elif ! in_path $var $PATH ; then
    
41.       return 2
    
42.     fi
    
43.   fi
    
44. }
    
45. 
    

復(fù)制代碼

其中后那個(gè)elif ! in_path $var $PATH 看不懂啊，請(qǐng)教各位。。。

Shell_HAT

調(diào)用函數(shù)in_path，$var和$PATH傳到函數(shù)里面之后就是$1和$2
還有哪里不懂？