Why -z? I have no idea. I will also routinely forget the ]; then part. I believe, if you write the then onto the next line, then you don’t need the semicolon. And then someone’s probably gonna tell me to use double-brackets [[ ]] instead, which probably does something.
Arguably, I never fully learned Bash syntax, but it also is just a stupid if-statement. There shouldn’t be that much complexity in it.
-z means zero length and mostly [[ ]] are used when you want to add multiple conditions. But there are also few test cases which are only in bash so they also need double brackets
Arguably, I never fully learned Bash syntax, but it also is just a stupid if-statement. There shouldn’t be that much complexity in it.
There isn’t. The syntax is
if COMMANDthenCOMMAND(s)...elseCOMMAND(s)...fi
I believe, if you write the then onto the next line, then you don’t need the semicolon.
Yes, but that’s true of all commands.
foo; bar; baz
is the same as
foobarbaz
All the ] and -z stuff has nothing to do with if. In your example, the command you’re running is literally called [. You’re passing it three arguments: -z, "$var", and ]. The ] argument is technically pointless but included for aesthetic reasons to match the opening ] (if you wanted to, you could also write test -z "$var" because [ is just another name for the test command).
Since you can logically negate the exit status of every command (technically, every pipeline) by prefixing a !, you could also write this as:
if ! test"$var"; then ...
The default mode of test (if given one argument) is to check whether it is non-empty.
Now, if you don’t want to deal with the vagaries of the test command and do a “native” string check, that would be:
My god… I’m so confused by your comment XD ! OP’s command is something I already came across, so I somehow got it… But your comment put me in total brain rot !
Here’s an example, I have looked up many times (like just now), which checks whether a string is empty:
var="" if [ -z "$var" ]; then echo "empty" else echo "not empty" fiWhy
-z? I have no idea. I will also routinely forget the]; thenpart. I believe, if you write thethenonto the next line, then you don’t need the semicolon. And then someone’s probably gonna tell me to use double-brackets[[ ]]instead, which probably does something.Arguably, I never fully learned Bash syntax, but it also is just a stupid if-statement. There shouldn’t be that much complexity in it.
-zmeans zero length and mostly[[ ]]are used when you want to add multiple conditions. But there are also few test cases which are only in bash so they also need double bracketsThere isn’t. The syntax is
if COMMANDthenCOMMAND(s)...elseCOMMAND(s)...fiYes, but that’s true of all commands.
is the same as
All the
]and-zstuff has nothing to do withif. In your example, the command you’re running is literally called[. You’re passing it three arguments:-z,"$var", and]. The]argument is technically pointless but included for aesthetic reasons to match the opening](if you wanted to, you could also writetest -z "$var"because[is just another name for thetestcommand).Since you can logically negate the exit status of every command (technically, every pipeline) by prefixing a
!, you could also write this as:if ! test "$var"; then ...The default mode of
test(if given one argument) is to check whether it is non-empty.Now, if you don’t want to deal with the vagaries of the
testcommand and do a “native” string check, that would be:case "$var" in "") echo "empty";; *) echo "not empty";;esacMy god… I’m so confused by your comment XD ! OP’s command is something I already came across, so I somehow got it… But your comment put me in total brain rot !
Now this is enlightening
From
man test(note that[ <expr> ]is just sugar fortest <expr>):-n STRING the length of STRING is nonzero -z STRING the length of STRING is zeroSo,
-zstands for Zero.Hope this helps you remember it!
You could write that as 1 line:
[ -z "$var" ] && echo "empty" || echo "no it aint"Incidentally, this is an anti-pattern: http://mywiki.wooledge.org/BashPitfalls#cmd1_.26.26_cmd2_.7C.7C_cmd3
@Tangentism @Ephera Did you mean:
echo "${var:-empty}${var:+no it aint}"?