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Shell编程 之 条件表达式
1 #!/bin/bash -
2 #===============================================================================
3 #
4 # FILE: condition_expression_test.sh
5 #
6 # USAGE: ./condition_expression_test.sh
7 #
8 # DESCRIPTION:
9 #
10 # OPTIONS: ---
11 # REQUIREMENTS: ---
12 # BUGS: ---
13 # NOTES: ---
14 # AUTHOR: daojoo, daojoo@qq.com
15 # ORGANIZATION: lit
16 # CREATED: 2012年03月10日 22时55分23秒 CST
17 # REVISION: ---
18 #===============================================================================
19
20 set -o nounset # Treat unset variables as an error
21
22 #以下内容来源于bash的man手册 [man bash]
23
24 #CONDITIONAL EXPRESSIONS
25 #Conditional expressions are used by the [[ compound
26 #command and the test and [ builtin commands to test file attributes and perform
27 #string and arithmetic comparisons. Expressions are formed from the following
28 #unary or binary primaries. If any file argument to one of the primaries is of
29 #the form /dev/fd/n, then file descriptor n is checked. If the file argument to
30 #one of the primaries is one of /dev/stdin, /dev/stdout, or /dev/stderr, file
31 #descriptor 0, 1, or 2, respectively, is checked.
32 #条件表达式
33 #1.用于何处？
34 # 用于[[组合命令中
35 # 用于test和[这两个内建命令中
36 #2.用来干什么？
37 # 测试文件属性
38 # 字符串和算术比较
39 #3.如何构建？
40 # 由参数、unary primaries、binary primaries构建
41 #
42 #Unless otherwise specified, primaries that operate on files follow symbolic
43 #links and operate on the target of the link, rather than the link itself.
44 #如果primaries后面的参数是一个符号链接，除非另行指明，否则运算符将作用于目标文件，
45 #而非链接本身
46 #
47 #When used with [[, The < and > operators sort lexicographically using the
48 #current locale.
49 #当使用[[p这个组合命令时，< 和 > 这两个二元操作符会使用当前locale将它的两个按字典排序
50 #
51 #See the description of the test builtin command (section SHELL BUILTIN COMMANDS
52 #below) for the handling of parameters (i.e. missing parameters).
53
54 #以下是primaries及测试
55
56 #-a file
57 # True if file exists.
58 # [all 只要文件存在]文件存在时为true
59 #-e file
60 # True if file exists.
61 # [exist 存在]作用同-a，存在即为true
62 touch test.txt;
63 if [ -a test.txt ]; then
64 echo "test.txt exists.";
65 fi
66 rm -f test.txt;
67 if [ ! -a test.txt ]; then
68 echo "test.txt not exists.";
69 fi
70 #output:
71 #test.txt exists.
72 #test.txt not exists.
73
74 #-b file
75 # True if file exists and is a block special file.
76 # [block 块]文件存在且是块文件时为true
77 BLOCK_FILE=/dev/sda;
78 if [ -b $BLOCK_FILE ]; then
79 echo "$BLOCK_FILE is a block file.";
80 fi
81 unset BLOCK_FILE;
82 #output:
83 #/dev/sda is a block file.
84
85 #-c file
86 # True if file exists and is a character special file.
87 # [character 字符]存在且是字符文件时为true
88
89
90 #-d file
91 # True if file exists and is a directory.
92 # [directory 目录]存在且是目录时为true
93 DIR=/
94 if [ -d $DIR ]; then
95 echo "$DIR is a directory.";
96 fi
97 unset DIR;
98 #output:
99 #/ is a directory.
100
101 #-f file
102 # True if file exists and is a regular file.
103 # [file 普通文件]存在且是普通文件时为true
104 REGULAR_FILE=/etc/profile ;
105 NONREGULAR_FILE=/dev/sda ;
106 if [ -f $REGULAR_FILE ]; then
107 echo "$REGULAR_FILE is a regular file." ;
108 else
109 echo "$REGULAR_FILE is not a regular file." ;
110 fi
111 if [ -f $NONREGULAR_FILE ]; then
112 echo "$NONREGULAR_FILE is a regular file." ;
113 else
114 echo "$NONREGULAR_FILE is not a regular file." ;
115 fi
116 unset REGULAR_FILE ;
117 unset NONREGULAR_FILE ;
118 #output:
119 #/etc/profile is a regular file.
120 #/dev/sda is not a regular file.
121
122 #-g file
123 # True if file exists and is set-group-id.
124 # [setgid]存在且文件属性为"......s..."时为true，其中.代表-,r,w,x中的任意一个
125 touch setgid.txt ;
126 chmod 6755 setgid.txt ;
127 if [ -g setgid.txt ]; then
128 echo "setgid.txt is set-group-id."
129 else
130 echo "setuid.txt is not set-user-id."
131 fi
132 chmod 0755 setgid.txt ;
133 if [ -g setgid.txt ]; then
134 echo "setgid.txt is set-group-id."
135 else
136 echo "setuid.txt is not set-user-id."
137 fi
138 rm -f setgid.txt ;
139 #output:
140 #setgid.txt is set-group-id.
141 #setuid.txt is not set-user-id.
142
143 #-L file
144 # True if file exists and is a symbolic link.
145 # [link 链接]同-h，存在且是符号链接时为true
146 #-h file
147 # True if file exists and is a symbolic link.
148 # 存在且是符号链接时为true
149 touch source.txt ;
150 ln -s source.txt target.txt ;
151 SOURCE=source.txt ;
152 TARGET=target.txt ;
153 if [ -h $SOURCE ] ; then
154 echo "$SOURCE is a symbolic link." ;
155 else
156 echo "$SOURCE is not a symbolic link." ;
157 fi
158 if [ -h $TARGET ] ; then
159 echo "$TARGET is a symbolic link." ;
160 else
161 echo "$TARGET is not a symbolic link." ;
162 fi
163 rm -f $SOURCE $TARGET ;
164 unset SOURCE TARGET ;
165 #output:
166 #source.txt is not a symbolic link.
167 #target.txt is a symbolic link.
168
169
170 #-k file
171 # True if file exists and its ``sticky‘‘ bit is set.
172 # 存在且文件属性中设置了t位时为true
173 TMP=/tmp ;
174 if [ -k $TMP ] ; then
175 echo "$TMP‘s \"sticky\" bit is set."
176 else
177 echo "$TMP‘s \"sticky\" bit is not set."
178 fi
179 unset TMP ;
180
181 #-p file
182 # True if file exists and is a named pipe (FIFO).
183 # [pipe 命名管道]存在且是命名管道时为true
184 #以下脚本需要以root身份执行
185 if [ $USER = "root" ]; then
186 FIFO=/proc/1/fd/4 ;
187 if [ -p $FD ] ; then
188 echo "$FD is a named pipe."
189 else
190 echo "$FD is not a named pipe."
191 fi
192 unset FIFO;
193 fi
194
195
196 #-r file
197 # True if file exists and is readable.
198 # [readable 可读]存在且可读时为true，注意不是只读
199 touch readable.txt ;
200 touch unreadable.txt ;
201 chmod 444 readable.txt ;
202 chmod 000 unreadable.txt ;
203 READABLE=readable.txt ;
204 UNREADABLE=unreadable.txt ;
205 if [ -r $READABLE ] ; then
206 echo "$READABLE is readable."
207 else
208 echo "$READABLE is unreadable."
209 fi
210 if [ -r $UNREADABLE ] ; then
211 echo "$UNREADABLE is readable."
212 else
213 echo "$UNREADABLE is unreadable."
214 fi
215 rm -f $READABLE $UNREADABLE ;
216 unset READABLE ;
217 unset UNREADABLE ;
218 #output:
219 #readable.txt is readable.
220 #unreadable.txt is unreadable.
221
222 #-s file
223 # True if file exists and has a size greater than zero.
224 # 存在且不为空时为true
225 touch test_file ;
226 TEST_FILE=test_file ;
227 if [ -s $TEST_FILE ] ; then
228 echo "$TEST_FILE has something."
229 else
230 echo "$TEST_FILE has nothing."
231 fi
232 echo "something" > $TEST_FILE ;
233 if [ -s $TEST_FILE ] ; then
234 echo "$TEST_FILE has something."
235 else
236 echo "$TEST_FILE has nothing."
237 fi
238 rm -f $TEST_FILE ;
239 unset TEST_FILE ;
240 #output:
241 #test_file has nothing.
242 #test_file has something.
243
244 #-t fd
245 # True if file descriptor fd is open and refers to a terminal.
246 # [terminal 终端]文件描述符已打开且关联了一个终端时为true
247 # 可用于判断一个脚本是运行于交互模式（终端模式）还是非交互模式（cron或at）
248 if [ $USER = "root" ]; then
249 FD=/proc/1/fd/4
250 if [ -t 0 ] ; then
251 echo "File descriptor $FD is open and refers to a terminal."
252 else
253 echo "File descriptor $FD is not open or not refers to a terminal."
254 fi
255 unset FD ;
256 fi
257 if [ -t 1 ] ; then
258 echo "File descriptor 1 is open and refers to a terminal."
259 else
260 echo "File descriptor 1 is not open or not refers to a terminal."
261 fi
262
263 #-u file
264 # True if file exists and its set-user-id bit is set.
265 # [setuid]存在且文件属性为"...s......"时为true，其中.代表-,r,w,x中的任意一个
266 SETUID=/usr/bin/passwd ;
267 if [ -u $SETUID ] ; then
268 echo "$SETUID‘s set-user-id bit is set." ;
269 else
270 echo "$SETUID‘s set-user-id bit is not set." ;
271 fi
272 unset SETUID ;
273 #output:
274 #/usr/bin/passwd‘s set-user-id bit is set.
275
276 #-w file
277 # True if file exists and is writable.
278 # [writable 可写]存在且可写时为true
279 touch writable.txt unwritable.txt ;
280 WRITABLE=writable.txt ;
281 chmod 666 $WRITABLE ;
282 UNWRITABLE=unwritable.txt ;
283 chmod 444 $UNWRITABLE ;
284 if [ -w $WRITABLE ] ; then
285 echo "$WRITABLE is writable."
286 else
287 echo "$WRITABLE is not writable."
288 fi
289 if [ -w $UNWRITABLE ] ; then
290 echo "$UNWRITABLE is writable."
291 else
292 echo "$UNWRITABLE is not writable."
293 fi
294 rm $WRITABLE $UNWRITABLE ;
295 unset WRITABLE UNWRITABLE ;
296 #output:
297 #writable.txt is writable.
298 #unwritable.txt is not writable.
299
300 #-x file
301 # True if file exists and is executable.
302 # [executable 可执行]存在且可执行时为true
303 if [ -x $0 ] ; then
304 echo "$0 is executable.";
305 else
306 echo "$0 is not executable.";
307 fi
308
309 #-O file
310 # True if file exists and is owned by the effective user id.
311 # [owner 属于]存在且文件的所有者为执行脚本的用户时为true
312 if [ -O $HOME ] ; then
313 echo -e "$HOME is owned by the effective user \"$USER\".";
314 else
315 echo -e "$HOME is not owned by the effective user \"$USER\".";
316 fi
317
318 #-G file
319 # True if file exists and is owned by the effective group id.
320 # [group 所属组]存在且文件的所属组为执行脚本的用户所在的组时为true
321 EFFECTIVE_GROUP=`groups | cut -f1 -d ‘ ‘` ;
322 if [ -G $HOME ] ; then
323 echo "$HOME is owned by the effective group \"$EFFECTIVE_GROUP\"." ;
324 else
325 echo "$HOME is not owned by the effective group \"$EFFECTIVE_GROUP\"." ;
326 fi
327 unset EFFECTIVE_GROUP ;
328
329
330 #-S file
331 # True if file exists and is a socket.
332 # [socket 套接字]存在且是套接字文件时为true
333
334 #-N file
335 # True if file exists and has been modified since it was last read.
336 # 存在且最后一次读取该文件时改变了文件的内容时为true
337 touch test.txt ;
338 TEST_FILE=test.txt ;
339 echo "test.txt" > $TEST_FILE ;
340 if [ -N $TEST_FILE ] ; then
341 echo "$TEST_FILE exists and has been modified since it was last read. "
342 else
343 echo "$TEST_FILE not exists or has not been modified since it was last read. "
344 fi
345 sleep 1 ; # 休眠1秒钟，否则看不出效果。
346 cat $TEST_FILE > /dev/null ;
347 if [ -N $TEST_FILE ] ; then
348 echo "$TEST_FILE exists and has been modified since it was last read. "
349 else
350 echo "$TEST_FILE not exists or has not been modified since it was last read. "
351 fi
352 rm $TEST_FILE ;
353 unset TEST_FILE ;
354 #output:
355 #test.txt exists and has been modified since it was last read.
356 #test.txt not exists or has not been modified since it was last read.
357
358 #file1 -nt file2
359 # True if file1 is newer (according to modification date) than file2, or if
360 # file1 exists and file2 does not.
361 # 当file1比file2新或file1存在而file2不存在时为true
362
363 #file1 -ot file2
364 # True if file1 is older than file2, or if file2 exists and file1 does not.
365 # 当file1比file2旧或file2存在而file1不存在时为true
366
367 #file1 -ef file2
368 # True if file1 and file2 refer to the same device and inode numbers.
369 # 当file1和file2引用相同的设备或具有相同的节点号时为true
370
371 #-o optname
372 # True if shell option optname is enabled. See the list of options under the
373 # description of the -o option to the set builtin below.
374
375 #-z string
376 # True if the length of string is zero.
377 # [zero]字符串长度等于0时为true
378
379 #string
380 #-n string
381 # True if the length of string is non-zero.
382 # 字符串不为空时为true
383
384 #string1 == string2
385 #string1 = string2
386 # True if the strings are equal. = should be used with the test command for
387 # POSIX conformance.
388 # string1和string2相同时为true
389
390 #string1 != string2
391 # True if the strings are not equal.
392 # string1和string2不同时为true
393
394 #string1 < string2
395 # True if string1 sorts before string2 lexicographically.
396 # string1在字典中排在string2之前时为true
397
398 #string1 > string2
399 # True if string1 sorts after string2 lexicographically.
400 # string1在字典中排在string2之后时为true
401
402 #arg1 OP arg2
403 # OP is one of -eq, -ne, -lt, -le, -gt, or -ge. These arithmetic binary
404 # operators return true if arg1 is equal to, not equal to, less than, less
405 # than or equal to, greater than, or greater than or equal to arg2,
406 # respectively. Arg1 and arg2 may be positive or negative integers.
407 # -eq equal to 等于
408 # -ne not equal to 不等于
409 # -lt less than 小于
410 # -le less than or equal to 小于或等于
411 # -gt greater than 大于
412 # -ge greater than or equal to 大于或等于
2 #===============================================================================
3 #
4 # FILE: condition_expression_test.sh
5 #
6 # USAGE: ./condition_expression_test.sh
7 #
8 # DESCRIPTION:
9 #
10 # OPTIONS: ---
11 # REQUIREMENTS: ---
12 # BUGS: ---
13 # NOTES: ---
14 # AUTHOR: daojoo, daojoo@qq.com
15 # ORGANIZATION: lit
16 # CREATED: 2012年03月10日 22时55分23秒 CST
17 # REVISION: ---
18 #===============================================================================
19
20 set -o nounset # Treat unset variables as an error
21
22 #以下内容来源于bash的man手册 [man bash]
23
24 #CONDITIONAL EXPRESSIONS
25 #Conditional expressions are used by the [[ compound
26 #command and the test and [ builtin commands to test file attributes and perform
27 #string and arithmetic comparisons. Expressions are formed from the following
28 #unary or binary primaries. If any file argument to one of the primaries is of
29 #the form /dev/fd/n, then file descriptor n is checked. If the file argument to
30 #one of the primaries is one of /dev/stdin, /dev/stdout, or /dev/stderr, file
31 #descriptor 0, 1, or 2, respectively, is checked.
32 #条件表达式
33 #1.用于何处？
34 # 用于[[组合命令中
35 # 用于test和[这两个内建命令中
36 #2.用来干什么？
37 # 测试文件属性
38 # 字符串和算术比较
39 #3.如何构建？
40 # 由参数、unary primaries、binary primaries构建
41 #
42 #Unless otherwise specified, primaries that operate on files follow symbolic
43 #links and operate on the target of the link, rather than the link itself.
44 #如果primaries后面的参数是一个符号链接，除非另行指明，否则运算符将作用于目标文件，
45 #而非链接本身
46 #
47 #When used with [[, The < and > operators sort lexicographically using the
48 #current locale.
49 #当使用[[p这个组合命令时，< 和 > 这两个二元操作符会使用当前locale将它的两个按字典排序
50 #
51 #See the description of the test builtin command (section SHELL BUILTIN COMMANDS
52 #below) for the handling of parameters (i.e. missing parameters).
53
54 #以下是primaries及测试
55
56 #-a file
57 # True if file exists.
58 # [all 只要文件存在]文件存在时为true
59 #-e file
60 # True if file exists.
61 # [exist 存在]作用同-a，存在即为true
62 touch test.txt;
63 if [ -a test.txt ]; then
64 echo "test.txt exists.";
65 fi
66 rm -f test.txt;
67 if [ ! -a test.txt ]; then
68 echo "test.txt not exists.";
69 fi
70 #output:
71 #test.txt exists.
72 #test.txt not exists.
73
74 #-b file
75 # True if file exists and is a block special file.
76 # [block 块]文件存在且是块文件时为true
77 BLOCK_FILE=/dev/sda;
78 if [ -b $BLOCK_FILE ]; then
79 echo "$BLOCK_FILE is a block file.";
80 fi
81 unset BLOCK_FILE;
82 #output:
83 #/dev/sda is a block file.
84
85 #-c file
86 # True if file exists and is a character special file.
87 # [character 字符]存在且是字符文件时为true
88
89
90 #-d file
91 # True if file exists and is a directory.
92 # [directory 目录]存在且是目录时为true
93 DIR=/
94 if [ -d $DIR ]; then
95 echo "$DIR is a directory.";
96 fi
97 unset DIR;
98 #output:
99 #/ is a directory.
100
101 #-f file
102 # True if file exists and is a regular file.
103 # [file 普通文件]存在且是普通文件时为true
104 REGULAR_FILE=/etc/profile ;
105 NONREGULAR_FILE=/dev/sda ;
106 if [ -f $REGULAR_FILE ]; then
107 echo "$REGULAR_FILE is a regular file." ;
108 else
109 echo "$REGULAR_FILE is not a regular file." ;
110 fi
111 if [ -f $NONREGULAR_FILE ]; then
112 echo "$NONREGULAR_FILE is a regular file." ;
113 else
114 echo "$NONREGULAR_FILE is not a regular file." ;
115 fi
116 unset REGULAR_FILE ;
117 unset NONREGULAR_FILE ;
118 #output:
119 #/etc/profile is a regular file.
120 #/dev/sda is not a regular file.
121
122 #-g file
123 # True if file exists and is set-group-id.
124 # [setgid]存在且文件属性为"......s..."时为true，其中.代表-,r,w,x中的任意一个
125 touch setgid.txt ;
126 chmod 6755 setgid.txt ;
127 if [ -g setgid.txt ]; then
128 echo "setgid.txt is set-group-id."
129 else
130 echo "setuid.txt is not set-user-id."
131 fi
132 chmod 0755 setgid.txt ;
133 if [ -g setgid.txt ]; then
134 echo "setgid.txt is set-group-id."
135 else
136 echo "setuid.txt is not set-user-id."
137 fi
138 rm -f setgid.txt ;
139 #output:
140 #setgid.txt is set-group-id.
141 #setuid.txt is not set-user-id.
142
143 #-L file
144 # True if file exists and is a symbolic link.
145 # [link 链接]同-h，存在且是符号链接时为true
146 #-h file
147 # True if file exists and is a symbolic link.
148 # 存在且是符号链接时为true
149 touch source.txt ;
150 ln -s source.txt target.txt ;
151 SOURCE=source.txt ;
152 TARGET=target.txt ;
153 if [ -h $SOURCE ] ; then
154 echo "$SOURCE is a symbolic link." ;
155 else
156 echo "$SOURCE is not a symbolic link." ;
157 fi
158 if [ -h $TARGET ] ; then
159 echo "$TARGET is a symbolic link." ;
160 else
161 echo "$TARGET is not a symbolic link." ;
162 fi
163 rm -f $SOURCE $TARGET ;
164 unset SOURCE TARGET ;
165 #output:
166 #source.txt is not a symbolic link.
167 #target.txt is a symbolic link.
168
169
170 #-k file
171 # True if file exists and its ``sticky‘‘ bit is set.
172 # 存在且文件属性中设置了t位时为true
173 TMP=/tmp ;
174 if [ -k $TMP ] ; then
175 echo "$TMP‘s \"sticky\" bit is set."
176 else
177 echo "$TMP‘s \"sticky\" bit is not set."
178 fi
179 unset TMP ;
180
181 #-p file
182 # True if file exists and is a named pipe (FIFO).
183 # [pipe 命名管道]存在且是命名管道时为true
184 #以下脚本需要以root身份执行
185 if [ $USER = "root" ]; then
186 FIFO=/proc/1/fd/4 ;
187 if [ -p $FD ] ; then
188 echo "$FD is a named pipe."
189 else
190 echo "$FD is not a named pipe."
191 fi
192 unset FIFO;
193 fi
194
195
196 #-r file
197 # True if file exists and is readable.
198 # [readable 可读]存在且可读时为true，注意不是只读
199 touch readable.txt ;
200 touch unreadable.txt ;
201 chmod 444 readable.txt ;
202 chmod 000 unreadable.txt ;
203 READABLE=readable.txt ;
204 UNREADABLE=unreadable.txt ;
205 if [ -r $READABLE ] ; then
206 echo "$READABLE is readable."
207 else
208 echo "$READABLE is unreadable."
209 fi
210 if [ -r $UNREADABLE ] ; then
211 echo "$UNREADABLE is readable."
212 else
213 echo "$UNREADABLE is unreadable."
214 fi
215 rm -f $READABLE $UNREADABLE ;
216 unset READABLE ;
217 unset UNREADABLE ;
218 #output:
219 #readable.txt is readable.
220 #unreadable.txt is unreadable.
221
222 #-s file
223 # True if file exists and has a size greater than zero.
224 # 存在且不为空时为true
225 touch test_file ;
226 TEST_FILE=test_file ;
227 if [ -s $TEST_FILE ] ; then
228 echo "$TEST_FILE has something."
229 else
230 echo "$TEST_FILE has nothing."
231 fi
232 echo "something" > $TEST_FILE ;
233 if [ -s $TEST_FILE ] ; then
234 echo "$TEST_FILE has something."
235 else
236 echo "$TEST_FILE has nothing."
237 fi
238 rm -f $TEST_FILE ;
239 unset TEST_FILE ;
240 #output:
241 #test_file has nothing.
242 #test_file has something.
243
244 #-t fd
245 # True if file descriptor fd is open and refers to a terminal.
246 # [terminal 终端]文件描述符已打开且关联了一个终端时为true
247 # 可用于判断一个脚本是运行于交互模式（终端模式）还是非交互模式（cron或at）
248 if [ $USER = "root" ]; then
249 FD=/proc/1/fd/4
250 if [ -t 0 ] ; then
251 echo "File descriptor $FD is open and refers to a terminal."
252 else
253 echo "File descriptor $FD is not open or not refers to a terminal."
254 fi
255 unset FD ;
256 fi
257 if [ -t 1 ] ; then
258 echo "File descriptor 1 is open and refers to a terminal."
259 else
260 echo "File descriptor 1 is not open or not refers to a terminal."
261 fi
262
263 #-u file
264 # True if file exists and its set-user-id bit is set.
265 # [setuid]存在且文件属性为"...s......"时为true，其中.代表-,r,w,x中的任意一个
266 SETUID=/usr/bin/passwd ;
267 if [ -u $SETUID ] ; then
268 echo "$SETUID‘s set-user-id bit is set." ;
269 else
270 echo "$SETUID‘s set-user-id bit is not set." ;
271 fi
272 unset SETUID ;
273 #output:
274 #/usr/bin/passwd‘s set-user-id bit is set.
275
276 #-w file
277 # True if file exists and is writable.
278 # [writable 可写]存在且可写时为true
279 touch writable.txt unwritable.txt ;
280 WRITABLE=writable.txt ;
281 chmod 666 $WRITABLE ;
282 UNWRITABLE=unwritable.txt ;
283 chmod 444 $UNWRITABLE ;
284 if [ -w $WRITABLE ] ; then
285 echo "$WRITABLE is writable."
286 else
287 echo "$WRITABLE is not writable."
288 fi
289 if [ -w $UNWRITABLE ] ; then
290 echo "$UNWRITABLE is writable."
291 else
292 echo "$UNWRITABLE is not writable."
293 fi
294 rm $WRITABLE $UNWRITABLE ;
295 unset WRITABLE UNWRITABLE ;
296 #output:
297 #writable.txt is writable.
298 #unwritable.txt is not writable.
299
300 #-x file
301 # True if file exists and is executable.
302 # [executable 可执行]存在且可执行时为true
303 if [ -x $0 ] ; then
304 echo "$0 is executable.";
305 else
306 echo "$0 is not executable.";
307 fi
308
309 #-O file
310 # True if file exists and is owned by the effective user id.
311 # [owner 属于]存在且文件的所有者为执行脚本的用户时为true
312 if [ -O $HOME ] ; then
313 echo -e "$HOME is owned by the effective user \"$USER\".";
314 else
315 echo -e "$HOME is not owned by the effective user \"$USER\".";
316 fi
317
318 #-G file
319 # True if file exists and is owned by the effective group id.
320 # [group 所属组]存在且文件的所属组为执行脚本的用户所在的组时为true
321 EFFECTIVE_GROUP=`groups | cut -f1 -d ‘ ‘` ;
322 if [ -G $HOME ] ; then
323 echo "$HOME is owned by the effective group \"$EFFECTIVE_GROUP\"." ;
324 else
325 echo "$HOME is not owned by the effective group \"$EFFECTIVE_GROUP\"." ;
326 fi
327 unset EFFECTIVE_GROUP ;
328
329
330 #-S file
331 # True if file exists and is a socket.
332 # [socket 套接字]存在且是套接字文件时为true
333
334 #-N file
335 # True if file exists and has been modified since it was last read.
336 # 存在且最后一次读取该文件时改变了文件的内容时为true
337 touch test.txt ;
338 TEST_FILE=test.txt ;
339 echo "test.txt" > $TEST_FILE ;
340 if [ -N $TEST_FILE ] ; then
341 echo "$TEST_FILE exists and has been modified since it was last read. "
342 else
343 echo "$TEST_FILE not exists or has not been modified since it was last read. "
344 fi
345 sleep 1 ; # 休眠1秒钟，否则看不出效果。
346 cat $TEST_FILE > /dev/null ;
347 if [ -N $TEST_FILE ] ; then
348 echo "$TEST_FILE exists and has been modified since it was last read. "
349 else
350 echo "$TEST_FILE not exists or has not been modified since it was last read. "
351 fi
352 rm $TEST_FILE ;
353 unset TEST_FILE ;
354 #output:
355 #test.txt exists and has been modified since it was last read.
356 #test.txt not exists or has not been modified since it was last read.
357
358 #file1 -nt file2
359 # True if file1 is newer (according to modification date) than file2, or if
360 # file1 exists and file2 does not.
361 # 当file1比file2新或file1存在而file2不存在时为true
362
363 #file1 -ot file2
364 # True if file1 is older than file2, or if file2 exists and file1 does not.
365 # 当file1比file2旧或file2存在而file1不存在时为true
366
367 #file1 -ef file2
368 # True if file1 and file2 refer to the same device and inode numbers.
369 # 当file1和file2引用相同的设备或具有相同的节点号时为true
370
371 #-o optname
372 # True if shell option optname is enabled. See the list of options under the
373 # description of the -o option to the set builtin below.
374
375 #-z string
376 # True if the length of string is zero.
377 # [zero]字符串长度等于0时为true
378
379 #string
380 #-n string
381 # True if the length of string is non-zero.
382 # 字符串不为空时为true
383
384 #string1 == string2
385 #string1 = string2
386 # True if the strings are equal. = should be used with the test command for
387 # POSIX conformance.
388 # string1和string2相同时为true
389
390 #string1 != string2
391 # True if the strings are not equal.
392 # string1和string2不同时为true
393
394 #string1 < string2
395 # True if string1 sorts before string2 lexicographically.
396 # string1在字典中排在string2之前时为true
397
398 #string1 > string2
399 # True if string1 sorts after string2 lexicographically.
400 # string1在字典中排在string2之后时为true
401
402 #arg1 OP arg2
403 # OP is one of -eq, -ne, -lt, -le, -gt, or -ge. These arithmetic binary
404 # operators return true if arg1 is equal to, not equal to, less than, less
405 # than or equal to, greater than, or greater than or equal to arg2,
406 # respectively. Arg1 and arg2 may be positive or negative integers.
407 # -eq equal to 等于
408 # -ne not equal to 不等于
409 # -lt less than 小于
410 # -le less than or equal to 小于或等于
411 # -gt greater than 大于
412 # -ge greater than or equal to 大于或等于
来自为知笔记(Wiz)
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