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Top Forums Shell Programming and Scripting Explain How ":=" works in shell scrpting Post 302395458 by Scott on Tuesday 16th of February 2010 06:45:37 AM
Old 02-16-2010
Hi.

I think the shell man page can explain it better than me Smilie

ksh description:
Quote:
${parameter:=word}
If parameter is not set or is null then set it to word; the value of the parameter is then substituted.
Positional parameters may not be assigned to in this way.
bash description:
Code:
${parameter:=word}
              Assign Default Values.  If parameter is unset or null, the expansion of word is assigned  to  parameter.
              The  value  of  parameter  is then substituted.  Positional parameters and special parameters may not be
              assigned to in this way.

 

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randomword(3)						     Library Functions Manual						     randomword(3)

NAME
randomword, randomchars, randomletters - Generate random passwords (Enhanced Security) LIBRARY
Security Library - libsecurity.so SYNOPSIS
int randomchars( char *string, unsigned short int minlen, unsigned short int maxlen, boolean restrict, long seed); int randomletters( char *string, unsigned short int minlen, unsigned short int maxlen, boolean restrict, long seed); int randomword( char *word, char *hyphenated_word, unsigned short int minlen, unsigned short int maxlen, boolean restrict, long seed); PARAMETERS
Points at a user-supplied space to contain a null-terminated password. Specifies the minimum length that a generated word can have. Spec- ifies the maximum length that a generated word can have. Specifies whether restrictions are to be imposed on the generated word. This is a boolean integer, where a non-zero integer indications restrictions and a 0 (zero) indicates no restrictions. Specifies an initial seed for the random number generator. Points at a user-supplied space to contain a null-terminated random pronounceable password. Contains the hyphenated version of the generated word. DESCRIPTION
These functions generate random passwords for use in password selection. All of them are generated by the system, based on seeds and set in the function. Such seeds can be created with the drand48(), rand(), or random() functions. The randomchars() function places a null-terminated password composed of random printable ASCII characters into the string parameter and returns the length of the generated string. The minlen parameter can equal maxlen, but cannot be greater than maxlen, and cannot be nega- tive. The user space preallocated is at least maxlen for string. The smaller minlen and maxlen are, the smaller the selection space of random words. The restrict parameter is 0 (zero) when no restrictions are placed on the generated word. It is nonzero when the words generated pass the tests of the acceptable_password() function. The seed parameter is used by the function only on the first time it is called; the parameter is ignored on subsequent calls. The randomletters() function places a null-terminated password composed of random lower-case letters into the string parameter and returns the length of the generated word. The minlen, maxlen, restrict, and seed parameters are the same as for the randomchars() function. The randomword() function places a null-terminated random pronounceable password into the word parameter and returns the length of the gen- erated word. The minlen, maxlen, restrict, and seed parameters are the same as for the randomchars() and randomletters() functions. The user space preallocated is at least 2*max - 1 for hyphenated_word. NOTES
The password generator relies on a random number generator that produces uniformly distributed integers. Because the password generator invokes the random number generator many times even for one word, the random number generator has to produce a uniform distribution. The period (distinct numbers produced given a particular seed) and number space (range of possible numbers) must both be large. The drand48() functions are used for this purpose. Programs using these functions must be compiled with -lsecurity. FILES
System password file. System group file. RELATED INFORMATION
Functions: acceptable_password(3), drand48(3), rand(3), random(3). Commands: login(1), passwd(1). delim off randomword(3)
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