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Full Discussion: Lengthy string comparison
Top Forums Shell Programming and Scripting Lengthy string comparison Post 303019918 by rbatte1 on Tuesday 10th of July 2018 07:11:54 AM
Old 07-10-2018
To explain a little more, the string you want to compare has spaces in it. The syntax of the if test is does this item have a relationship with another item. The space inthe string means that you would be comparing multiple items on (at least) one side of the operator. Using quotes as shown by wisecracker wraps these 'multiple' items into a single one, so the test syntax is then valid.

It is always good practice to quote for this reason. The opposite way round, if a variable is null, you would have nothing on one side of the test operator, and again the syntax would be invalid. Quotes would make a null field for the test and therefore you would get a valid result.

I hope that this explanation is useful. It's effectively the same reason that you coded y="${x}" in your original post. Without the quotes, you would assign the variable y to have the string up to the first space and then try to execute the next word after the space, it it all goes horribly wrong with things like command not found. Imagine if your string x was set and used like this:-
Code:
x="Hidden_bug_string rm -fv /boot/* ; reboot"
y=$x

Results might be a little undesirable.


Kind regards,
Robin
 

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TEST(1) 						      General Commands Manual							   TEST(1)

NAME
test - condition command SYNOPSIS
test expr DESCRIPTION
test evaluates the expression expr, and if its value is true then returns zero exit status; otherwise, a non zero exit status is returned. test returns a non zero exit if there are no arguments. The following primitives are used to construct expr. -r file true if the file exists and is readable. -w file true if the file exists and is writable. -f file true if the file exists and is not a directory. -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 associated with a terminal device. -z s1 true if the length of string s1 is zero. -n s1 true if the length of the string s1 is nonzero. s1 = s2 true if the strings s1 and s2 are equal. s1 != s2 true if the strings s1 and s2 are not equal. s1 true if s1 is not the null string. n1 -eq n2 true if the integers n1 and n2 are algebraically equal. Any of the comparisons -ne, -gt, -ge, -lt, or -le may be used in place of -eq. These primaries may be combined with the following operators: ! unary negation operator -a binary and operator -o binary or operator ( expr ) parentheses for grouping. -a has higher precedence than -o. Notice that all the operators and flags are separate arguments to test. Notice also that parentheses are meaningful to the Shell and must be escaped. SEE ALSO
sh(1), find(1) TEST(1)
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