[SOLVED] [[ ! -w ${file} ]] - What is the "!" doing and what is the "-w" doing?

orri23 · 05-10-2017, 05:52 AM

if [[ ! -w ${file} ]] ; then
echo "You do not have write permission."

What is this doing? I don't seem to find much or anything at all about "-w", and little about "!". Thank you if someone helps.

hydrurga · 05-10-2017, 06:04 AM

File test operators: http://tldp.org/LDP/abs/html/fto.html

! is the negation operator

It's worth your while working through the Advanced Bash-scripting Guide:

http://tldp.org/LDP/abs/html/part1.html

For a gentler introduction:

https://www.howtoforge.com/tutorial/...pting-lessons/

pan64 · 05-10-2017, 06:12 AM

you may also try: man test (although it is not the same, but quite similar), and man bash (look for conditional expressions)

BW-userx · 05-10-2017, 09:04 AM

7.3. Other Comparison Operators

some more to look at ..

the use of the ! (not) in that example is correct logic. If you are checking for something that is 'not' to be true. In other words, if the value you're looking for is not there then it returns 'true' then act upon it accordingly.

Code:

if [[ ! -w ${file} ]] ; then

if it is not working then:
The question then is the code to get the value into your variable named 'file'. if the value within the variable is there and correct, then it is your logic that is now backwards.

Logical Not !

chrism01 · 05-10-2017, 08:38 PM

Actually "if $file is not writable (for user running the test) then ..."
See link provided by hydrurga