[请教]如何随机的生成一个字符串？[请教]

小鹭

1. #!/bin/bash
   
2. # May need to be invoked with #!/bin/bash2 on older machines.
   
3. #
   
4. # Random password generator for bash 2.x by Antek Sawicki <tenox@tenox.tc>,
   
5. # who generously gave permission to the document author to use it here.
   
6. #
   
7. # ==> Comments added by document author ==>
   
8. MATRIX="0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz"
   
9. LENGTH="8"
   
10. # ==> May change 'LENGTH' for longer password, of course.
    
11. while [ "${n:=1}" −le "$LENGTH" ]
    
12. # ==> Recall that := is "default substitution" operator.
    
13. # ==> So, if 'n' has not been initialized, set it to 1.
    
14. do
    
15. PASS="$PASS${MATRIX:$(($RANDOM%${#MATRIX})):1}"
    
16. # ==> Very clever, but tricky.
    
17. # ==> Starting from the innermost nesting...
    
18. # ==> ${#MATRIX} returns length of array MATRIX.
    
19. # ==> $RANDOM%${#MATRIX} returns random number between 1
    
20. # ==> and length of MATRIX − 1.
    
21. # ==> ${MATRIX:$(($RANDOM%${#MATRIX})):1}
    
22. # ==> returns expansion of MATRIX at random position, by length 1.
    
23. # ==> See {var:pos:len} parameter substitution in Section 3.3.1
    
24. # ==> and following examples.
    
25. # ==> PASS=... simply pastes this result onto previous PASS (concatenation).
    
26. # ==> To visualize this more clearly, uncomment the following line
    
27. # ==> echo "$PASS"
    
28. # ==> to see PASS being built up,
    
29. # ==> one character at a time, each iteration of the loop.
    
30. let n+=1
    
31. # ==> Increment 'n' for next pass.
    
32. done
    
33. echo "$PASS" # ==> Or, redirect to file, as desired.
    
34. exit 0

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