Linux Shell if [n] Use method correctly __linux

if [str1 = str2] When two strings have the same content, the length is true
If [str1!= str2] True when string str1 and str2 are unequal
If [-N str1] is true when the length of the string is greater than 0 (string non-empty)
If [-Z str1] is true when the length of the string is 0 (empty string)
If [str1] is true when string str1 is Non-null

The shell uses-N to determine that the string is non-null.

Error usage:

args=$*

If [-N $ARGS]

Then

Print "with argument"

Fi

print "Without argument"

Regardless of the pass parameter, always enter the if inside.

Reason: Because the IF statement is equivalent to if [-N],shell will treat it as if [str1] without "", n is not null, so it is positive.

Correct usage: You need to add double quotes, or "$ARGS", to the $args.

args=$*

If [-N "$ARGS"]

Then

Print "with argument"

Fi

print "Without argument"

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