Basic usage of strings in the shell

Objective

Today, when writing a script, found that the previous phase used some of the usage is still need to go to Baidu Search, and find the answer also need to filter, delay writing script time, this article on the comparison between the string and logical judgments are very detailed, reference to other people's work, resource sharing.

This film mainly describes some of the considerations in string comparisons

The main include string equality, unequal, length, empty string, and logical and logical, or the content, see the following script:

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2. #!/bin/bash
4. # test String Order
8. A= "SS"
10. b= "ABC"
12. c= "SS"
16. echo "----------------------------------------------------------------------------"
18. echo "Test for string compare with \"!=\ ", \" =\ ", \"-z\ ", \"-n\ ", was a null str; test string is \" $a \ "and \" $b \ ""
20. echo "----------------------------------------------------------------------------"
24. echo "*************----------*********************"
28. echo "-----------"
30. echo "Test \" =\ "equals arithmetic, compares two strings equal"
32. echo "-----------"
34. echo "if [\ $a = \ $b]; Then use = to compare two strings are equal, note is not the = = symbol, note that the space symbol in the statement must be reserved, some of the following statements in the space format and the sentence similar to the "
36. if [$a = $b]; Then
38. echo "$a = = $b: a = B"
40. Else
42. echo "-----------"
44. echo "Test \" "!=\", not Equal, compares two strings of unequal "
46. echo "-----------"
48. if [$a! = $c]; Then
50. echo "$a = = $c: a!=c"
52. Else
54. echo "$a = = $c: a ==c"
56. Fi
58. Fi
60. echo "-----------"
62. echo "Test \"-z\ ", string length is 0 operation, 0 returns True"
64. echo "-----------"
66. If [-Z $a]
68. Then
70. echo "-Z $a: string length 0"
72. Else
74. echo "-Z $a: string length is not 0"
76. Fi
78. echo "-----------"
80. echo "Test \"-n\, string length not 0 operation, not 0 return true "
82. echo "-----------"
84. If [-N $a]
86. Then
88. echo "-N $a: string length not 0"
90. Else
92. echo "-N $a: string length 0"
94. Fi
96. echo "-----------"
98. echo "Test is a null str"
100. echo "-----------"
102. If [$a]
104. Then
106. echo "$a: String not empty"
108. Else
110. echo "$a: string is empty"
112. Fi
124. A= "AAA"
126. b= "BBB"
128. echo "----------------------------------------------------------------------------"
130. echo "test string with \" &&\ ", \" | | \ "; Test string is \" $a \ "and \" $b \ ""
132. echo "----------------------------------------------------------------------------"
134. echo "-----------"
136. echo "Test \" &&\ ", Logic and Operations"
138. echo "-----------"
140. if [[$a = $a && $b = $b]]
142. Then
144. echo "[[\ $a = \ $a && \ $b = \ $b]] returns True"
146. Else
148. echo "[[\ $a = \ $a && \ $b = \ $b]] returns false"
150. Fi
154. echo "-----------"
156. echo "Test \" | | \ ", logical OR operation"
158. echo "-----------"
160. if [[$a = $b | | $b = $b]]
162. Then
164. echo "[[\ $a = \ $b | | \ $b = \ $b]] returns True "
166. Else
168. echo "[[\ $a = \ $b | | \ $b = \ $b]] returns false "
170. Fi
178. echo "*************----------*********************"

Basic string usage in the shell