有关判断变量是否为空的疑问---新年也不忘写脚本啊有木有！

reyleon

回复 5# wwr


    [ ! -z "$var" ] 跟 [ -n "$var" ] 是一个效果

1. [root@centos ~]# man test
   
2. TEST(1)                          User Commands                         TEST(1)
   
3. 
   
4. NAME
   
5.        test - check file types and compare values
   
6. 
   
7. SYNOPSIS
   
8.        test EXPRESSION
   
9.        test
   
10. 
    
11.        [ EXPRESSION ]
    
12.        [ ]
    
13.        [ OPTION
    
14. 
    
15. DESCRIPTION
    
16.        Exit with the status determined by EXPRESSION.
    
17. 
    
18.        --help display this help and exit
    
19. 
    
20.        --version
    
21.               output version information and exit
    
22. 
    
23.        An omitted EXPRESSION defaults to false.  Otherwise, EXPRESSION is true or false and sets exit status.  It is one of:
    
24. 
    
25.        ( EXPRESSION )
    
26.               EXPRESSION is true
    
27. 
    
28.        ! EXPRESSION
    
29.               EXPRESSION is false
    
30. 
    
31.        EXPRESSION1 -a EXPRESSION2
    
32.               both EXPRESSION1 and EXPRESSION2 are true
    
33. 
    
34.        EXPRESSION1 -o EXPRESSION2
    
35.               either EXPRESSION1 or EXPRESSION2 is true
    
36. 
    
37.        -n STRING
    
38.               the length of STRING is nonzero
    
39. 
    
40.        STRING equivalent to -n STRING
    
41. 
    
42.        -z STRING
    
43.               the length of STRING is zero
    
44. 
    
45.        STRING1 = STRING2
    
46.               the strings are equal
    
47. 
    
48.        STRING1 != STRING2
    
49.               the strings are not equal
    
50. 
    
51.        INTEGER1 -eq INTEGER2
    
52.               INTEGER1 is equal to INTEGER2
    
53. 
    
54.        INTEGER1 -ge INTEGER2
    
55.               INTEGER1 is greater than or equal to INTEGER2
    
56. 
    
57.        INTEGER1 -gt INTEGER2
    
58.               INTEGER1 is greater than INTEGER2
    
59. 
    
60.        INTEGER1 -le INTEGER2
    
61.               INTEGER1 is less than or equal to INTEGER2
    
62. 
    
63.        INTEGER1 -lt INTEGER2
    
64.               INTEGER1 is less than INTEGER2
    
65. 
    
66.        INTEGER1 -ne INTEGER2
    
67.               INTEGER1 is not equal to INTEGER2
    
68. 
    
69.        FILE1 -ef FILE2
    
70.               FILE1 and FILE2 have the same device and inode numbers
    
71. 
    
72.        FILE1 -nt FILE2
    
73.               FILE1 is newer (modification date) than FILE2
    
74. 
    
75.        FILE1 -ot FILE2
    
76.               FILE1 is older than FILE2
    
77. 
    
78.        -b FILE
    
79.               FILE exists and is block special
    
80. 
    
81.        -c FILE
    
82.               FILE exists and is character special
    
83. 
    
84.        -d FILE
    
85.               FILE exists and is a directory
    
86. 
    
87.        -e FILE
    
88.               FILE exists
    
89. 
    
90.        -f FILE
    
91.               FILE exists and is a regular file
    
92. 
    
93.        -g FILE
    
94.               FILE exists and is set-group-ID
    
95. 
    
96.        -G FILE
    
97.               FILE exists and is owned by the effective group ID
    
98. 
    
99.        -h FILE
    
100.               FILE exists and is a symbolic link (same as -L)
     
101. 
     
102.        -k FILE
     
103.               FILE exists and has its sticky bit set
     
104. 
     
105.        -L FILE
     
106.               FILE exists and is a symbolic link (same as -h)
     
107. 
     
108.        -O FILE
     
109.               FILE exists and is owned by the effective user ID
     
110. 
     
111.        -p FILE
     
112.               FILE exists and is a named pipe
     
113. 
     
114.        -r FILE
     
115.               FILE exists and read permission is granted
     
116. 
     
117.        -s FILE
     
118.               FILE exists and has a size greater than zero
     
119. 
     
120.        -S FILE
     
121.               FILE exists and is a socket
     
122. 
     
123.        -t FD  file descriptor FD is opened on a terminal
     
124. 
     
125.        -u FILE
     
126.               FILE exists and its set-user-ID bit is set
     
127. 
     
128.        -w FILE
     
129.               FILE exists and write permission is granted
     
130. 
     
131.        -x FILE
     
132.               FILE exists and execute (or search) permission is granted
     
133. 
     
134.        Except  for  -h and -L, all FILE-related tests dereference symbolic links.  Beware that parentheses need to be escaped (e.g., by back-
     
135.        slashes) for shells.  INTEGER may also be -l STRING, which evaluates to the length of STRING.
     
136. 
     
137.        NOTE: your shell may have its own version of test and/or [, which usually supersedes the version described here.  Please refer to your
     
138.        shell’s documentation for details about the options it supports.
     
139. 
     
140. AUTHOR
     
141.        Written by Kevin Braunsdorf and Matthew Bradburn.
     
142. 
     
143. REPORTING BUGS
     
144.        Report bugs to <bug-coreutils@gnu.org>.
     
145. 
     
146. COPYRIGHT
     
147.        Copyright ? 2006 Free Software Foundation, Inc.
     
148.        This   is   free   software.    You   may   redistribute   copies   of   it  under  the  terms  of  the  GNU  General  Public  License
     
149.        <http://www.gnu.org/licenses/gpl.html>.  There is NO WARRANTY, to the extent permitted by law.
     
150. 
     
151. SEE ALSO
     
152.        The full documentation for test is maintained as a Texinfo manual.  If the info and test programs are properly installed at your site,
     
153.        the command
     
154. 
     
155.               info test
     
156. 
     
157.        should give you access to the complete manual.
     
158. 
     
159. test 5.97                        February 2010                         TEST(1)

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winway1988

回复 8# waker


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