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Top Forums Shell Programming and Scripting Change existing variable value only user enters non-empty string. Post 302422915 by kchinnam on Wednesday 19th of May 2010 06:53:49 PM
Old 05-19-2010
Murphy, your suggestion worked.

Code:
$>  test.sh  
Press Enter to select existing value 

uid[scott]:                                 # Selected Enter here.
uid --> scott

$>  test.sh
Press Enter to select existing value 

uid[scott]: aaaaa
0000000 141 141 141 141 141 012
           a   a   a   a   a  \n
            6161    6161    610a
0000006
uid --> aaaaa

I still could not understand why I can't use [ ! -n string ] instead of [ -z string ] or vice-versa .
Here is what the reference page I am looking at says about these two condition checking flags for ksh.

Code:
-z string	       --->         True if length of string is zero
-n string	       --->         True if length of string is non-zero

Can someone explain what are true differences between -z, -n flags !!? Where can I find true reference for this?

Last edited by kchinnam; 05-19-2010 at 08:02 PM.. Reason: formatting adjustments
 

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TEST(1) 						      General Commands Manual							   TEST(1)

NAME
test - set status according to condition SYNOPSIS
test expr DESCRIPTION
Test evaluates the expression expr. If the value is true the exit status is null; otherwise the exit status is non-null. If there are no arguments the exit status is non-null. The following primitives are used to construct expr. -r file True if the file exists (is accessible) and is readable. -w file True if the file exists and is writable. -x file True if the file exists and has execute permission. -e file True if the file exists. -f file True if the file exists and is a plain file. -d file True if the file exists and is a directory. -s file True if the file exists and has a size greater than zero. -t fildes True if the open file whose file descriptor number is fildes (1 by default) is the same file as /dev/cons. -A file True if the file exists and is append-only. -L file True if the file exists and is exclusive-use. -Tfile True if the file exists and is temporary. s1 = s2 True if the strings s1 and s2 are identical. s1 != s2 True if the strings s1 and s2 are not identical. s1 True if s1 is not the null string. (Deprecated.) -n s1 True if the length of string s1 is non-zero. -z s1 True if the length of string s1 is zero. n1 -eq n2 True if the integers n1 and n2 are arithmetically equal. Any of the comparisons -ne, -gt, -ge, -lt, or -le may be used in place of -eq. The (nonstandard) construct -l string, meaning the length of string, may be used in place of an integer. a -nt b True if file a is newer than (modified after) file b. a -ot b True if file a is older than (modified before) file b. f -older t True if file f is older than (modified before) time t. If t is a integer followed by the letters y(years), M(months), d(days), h(hours), m(minutes), or s(seconds), it represents current time minus the specified time. If there is no letter, it represents seconds since epoch. You can also concatenate mixed units. For example, 3d12h means three days and twelve hours ago. These primaries may be combined with the following operators: ! unary negation operator -o binary or operator -a binary and operator; higher precedence than -o ( expr ) parentheses for grouping. The primitives -b, -u, -g, and -s return false; they are recognized for compatibility with POSIX. Notice that all the operators and flags are separate arguments to test. Notice also that parentheses and equal signs are meaningful to rc and must be enclosed in quotes. EXAMPLES
Test is a dubious way to check for specific character strings: it uses a process to do what an rc(1) match or switch statement can do. The first example is not only inefficient but wrong, because test understands the purported string "-c" as an option. if (test $1 '=' "-c") echo OK # wrong! A better way is if (~ $1 -c) echo OK Test whether is in the current directory. test -f abc -o -d abc SOURCE
/src/cmd/test.c SEE ALSO
rc(1) TEST(1)
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