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I am fixing some old bash scripts I often see
if [[ -n $VARIABLE ]]; then
syntax I tried to google it but could find why "-n" is used for, following is what I know
Comparisons:
-eq equal to
-ne not equal to
-lt less than
-le less than or equal to
-gt greater than
-ge greater than or equal to
File Operations:
-s file exists and is not empty
-f file exists and is not a directory
-d directory exists
-x file is executable
-w file is writable
-r file is readable
would anyone let me know what -n do ?
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The [[ ... ]] part allows to test a condition using operators. Think of it as an if statement. In your example, you're using the -s operator, which tests that the referenced file is not empty. Copy link CC BY-SA 3.0.
The closing bracket tells test where the expression ends. The double brackets ([[) are a bash built in and can replace the external call to test.
The -z flag is a parameter that checks if the length of a variable is zero and returns true if it is zero. In the example below, the -z flag is used with the test command, and it is tested whether the given string is empty. Bash.
The special shell variable IFS determines how Bash recognizes word boundaries while splitting a sequence of character strings. The default value of IFS is a three-character string comprising a space, tab, and newline: $ echo "$IFS" | cat -et ^I$ $
help test would tell you:
String operators:
....
-n STRING
STRING True if string is not empty.
If $VARIABLE is a string, then [ -n $VARIABLE ] is true if the length of $VARIABLE is non-zero.
Also, [ -n $VARIABLE ] is equivalent with: [ $VARIABLE ], when and only when $VARIABLE is a string.
More about: Introduction to if
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