方法一：

locate_library() { [ ! "$1*" = "`echo $1*`" ]; }

用法：

# Look for PAM (done weirdly due to distribution bugs (e.g. Debian) or the
# crypt library.
if find_func pam_start sysdeputil.o; then
  locate_library /lib/libpam.so.0 && echo "/lib/libpam.so.0";
  locate_library /usr/lib/libpam.so && echo
 
 "-lpam";
  locate_library /usr/lib64/libpam.so && echo "-lpam";
  # HP-UX ends shared libraries with .sl
  locate_library /usr/lib/libpam.sl && echo "-lpam";
  # AIX ends shared libraries with .a
  locate_library /usr/lib/libpam.a && echo "-lpam";
else
  locate_library /lib/libcrypt.so && echo
 
 "-lcrypt";
  locate_library /usr/lib/libcrypt.so && echo "-lcrypt";
  locate_library /usr/lib64/libcrypt.so && echo "-lcrypt";
fi

方法二：

#!/bin/sh  

myPath="/var/log/httpd/"  
myFile="/var/log/httpd/access.log"  

#這裡的-x 引數判斷$myPath是否存在並且是否具有可執行許可權  
if [ ! -x "$myPath"]; then  
　　mkdir "$myPath"  
fi
 
  

#這裡的-d 引數判斷$myPath是否存在  
if [ ! -d "$myPath"]; then  
　　mkdir "$myPath"  
fi  

#這裡的-f引數判斷$myFile是否存在  
if [ ! -f "$myFile" ]; then  
　　touch "$myFile"  
fi  

#其他引數還有-n,-n是判斷一個變數是否是否有值  
if [ ! -n "$myVar" ]; then  
　　echo "$myVar is empty"  
　　exit 0  
fi  

#兩個變數判斷是否相等  
if [ "$var1" = "$var2" ]; then  
　　echo '$var1 eq $var2'  
else  
　　echo '$var1 not eq $var2'  
fi  

各種判斷標識及含義如下：

-a file exists.
-b file exists and is a block special file.
-c file exists and is a character special file.
-d file exists and is a directory.
-e file exists (just the same as -a).
-f file exists and is a regular file.
-g file exists and has its setgid(2) bit set.
-G file exists and has the same group ID as this process.
-k file exists and has its sticky bit set.
-L file exists and is a symbolic link.
-n string length is not zero.
-o Named option is set on.
-O file exists and is owned by the user ID of this process.
-p file exists and is a first in, first out (FIFO) special file or
named pipe.
-r file exists and is readable by the current process.
-s file exists and has a size greater than zero.
-S file exists and is a socket.
-t file descriptor number fildes is open and associated with a
terminal device.
-u file exists and has its setuid(2) bit set.
-w file exists and is writable by the current process.
-x file exists and is executable by the current process.
-z string length is zero.