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Okay, so within my script (this is my first time working with Bash) I am being met with two unary operator expected errors. The code itself is actually working fine, but it's presenting me with these errors at runtime:
[: !=: unary operator expected
For the line:
if [ ${netmask[1]} != "" ]; do
So for the first error, it's thrown when ${netmask[1]} is "" (null). I have tried multiple ideas and still can't get it to work without returning that error in the process.
I solved it by adding quotation marks (grrr)
if [ "${netmask[1]}" != "" ]; do
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Here, due to the blank value in the variable, the left side of the comparison expression disappears. In effect, we're left with a single argument for the equality check (eq) operator. The eq operator is a binary operator and needs two arguments, therefore, Bash complains with “unary operator expected”.
How to Use the Bash Sleep Command. Sleep is a very versatile command with a very simple syntax. It is as easy as typing sleep N . This will pause your script for N seconds, with N being either a positive integer or a floating point number.
The not equal function in Ubuntu bash is denoted by the symbol “-ne,” which would be the initial character of “not equal.” Also included is the “! =” operator that is used to indicate the not equal condition.
To find out if a bash variable is empty: Return true if a bash variable is unset or set to the empty string: if [ -z "$var" ]; Another option: [ -z "$var" ] && echo "Empty" Determine if a bash variable is empty: [[ ! -z "$var" ]] && echo "Not empty" || echo "Empty"
If you want to check for the null value for a variable, use the -z operator:
if [ -z "${netmask[1]}" ]; then
On example:
VAR=""
if [ -z "$VAR" ]; then
echo This will get printed
fi
Please note the parentheses around the variable: "$VAR".
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