I would like to test both variable in the same if condition.
Currently I am using [[ $var ]] to test one but the same for two variable do not work.
In order to do that I tried :
if [[ &var1 && &var2 ]]; then
or
if [[ &ipAddress ]] && [[ &bcastAddress ]]; then
Is there a limitation ?
You can use this combined test:
[[ -z "${var1}${var2}" ]]
OR separate tests in same if condition:
[[ -z "$var1" && -z "$var2" ]]
I often use arithmetic for these sorts of things. For example:
case "$(((!${#var1}&&!${#var2})*${#ip}))" in
(0) ! echo ERROR;;
(${#bcast}) echo '$ips len is equal to $bcasts and neither are zero';;
esac
Of course, you don't need the case there:
[ "${#var1}${#var2}" -eq "$(((${#ip}&&${#bcast})?0:-1))" ] || handle_it
Related
my if condition with gt compare value and also if the value is null, but I want that gt compare null value, I just want that he compare only value
res=''
toto=5
if [[ "$toto" -gt "$res" ]]; then
...
else
...
fi
fi
solution is that, but not very good
if [[ ! -z "$res" ]]; then
if [[ "$toto" -gt "$res" ]]; then
...
else
...
fi
fi
Use &&.
if [[ ! -z "$res" && "$toto" -gt "$res" ]]
Other improvements you could make:
Replace ! -z with -n.
Remove unnecessary quotes.
Use ((...)) for numerical comparisons.
if [[ -n $res ]] && ((toto > res))
This Shellcheck-clean code handles empty $res in another way:
#! /bin/bash
res=''
toto=5
if [[ -z $res ]] ; then
: # $res is empty so don't compare with $toto
elif (( toto > res )); then
echo 'toto is greater than res'
else
echo 'toto is less than or equal to res'
fi
However, it's debatable whether it's better or worse than the "not very good" option suggested in the question. Deeper nesting is usually worse, but if-the-else chains are best avoided. The only advantage I would claim for the code in this answer is that it has a convenient place to put a helpful comment if one is useful.
I am writing a bash script that sometimes will use environment variables GIT_DIR and GIT_WORK_TREE. The bash script can only operate correctly if either both variables exist or neither exist. In case there's a technical difference, it makes no difference
This works, but there has to be a better way:
if [[ -z "${GIT_DIR}" ]]; then
_GIT_DIR_EXISTS=0
else
_GIT_DIR_EXISTS=1
fi
if [[ -z "${GIT_WORK_TREE}" ]]; then
_GIT_WORK_TREE_EXISTS=0
else
_GIT_WORK_TREE_EXISTS=1
fi
if [[ "${_GIT_DIR_EXISTS}" -ne "${_GIT_WORK_TREE_EXISTS}" ]]; then
echo "GIT_DIR is ${GIT_DIR}"
echo "GIT_WORK_TREE is ${GIT_WORK_TREE}"
echo "Both or none must exist"
exit 1
fi
I tried:
if [[ (-z "${GIT_DIR}") -ne (-z "${GIT_WORK_TREE}") ]]; then
But that gives this error:
bash: syntax error in conditional expression
bash: syntax error near '-ne'
I then resorted to trying semi-random things, with varying errors:
if [[ -z "${GIT_DIR}" -ne -z "${GIT_WORK_TREE}" ]]; then
if [[ [-z "${GIT_DIR}"] -ne [-z "${GIT_WORK_TREE}"] ]]; then
if [[ [[-z "${GIT_DIR}"]] -ne [[-z "${GIT_WORK_TREE}"]] ]]; then
if [[ -z "${GIT_DIR}" ]] ^ [[ -z "${GIT_WORK_TREE}" ]]; then
if { [[ -z "${GIT_DIR}" ]] } -ne { [[ -z "${GIT_WORK_TREE}" ]] }; then
if [[ (( -z "${GIT_DIR}" )) -ne (( -z "${GIT_WORK_TREE}" )) ]]; then
I tried:
if [[ $(test -z "${GIT_DIR}") -ne $(test -z "${GIT_WORK_TREE}") ]]; then
But realized that doesn't work because it's a sub-process, and they'd need to be exported. as Socowl comments, this compares the outputs of the test commands which output nothing, not their exit statuses.
I apologize if this is a duplicate. I've searched here and google for a while, and must not be using the right terminology.
How about this:
if [[ "${GIT_DIR:+set}" != "${GIT_WORK_TREE:+set}" ]]; then
echo "GIT_DIR is '${GIT_DIR}'"
echo "GIT_WORK_TREE is '${GIT_WORK_TREE}'"
echo "Both or none must exist"
exit 1
fi
Explanation: ${var:+value} is a variant of parameter expansion that gives "value" if var is set to a nonempty string, or the empty string if var is unset or empty. So if both vars are unset/empty, it becomes if [[ "" != "" ]]; then, and if they're both set it becomes if [[ "set" != "set" ]]; then etc.
BTW, if you want to test whether the variables are set at all (even if to the empty string), use ${var+value} (note the lack of colon). The bash manual lists the :+ version, but not the + version.
I'm trying to write an if statement in bash that will exit if the variable supplied is not an integer. I will eventually be nesting this if statement within a while loop.
When I do run this I am getting an syntax error.
#!/bin/bash
if [ $f1 != ^[0-9]+$ ]
then
exit 1
fi
I have always like the integer test using the equality test construct:
[ $var -eq $var 2>/dev/null ] || exit 1
If var is not an integer, the equality fails due to the error generated. It is also POSIX compliant as it doesn't rely on character classes or the bash [[ construct.
You better negate the condition like this:
if [[ ! "$f1" =~ ^[0-9]+$ ]]; then
exit 1
fi
note the [[ and ]] syntax for the regular expressions, together with ! to negate it. Then, we use =~ for regexs.
Test
$ r=23a
$ [[ ! "$r" =~ ^[0-9]+$ ]] && echo "no digit" || echo "digit"
no digit
$ r=23
$ [[ ! "$r" =~ ^[0-9]+$ ]] && echo "no digit" || echo "digit"
digit
I am attempting to run a block of code if one flag is set to true and the other is set to false. ie
var1=true
var2=false
if [[ $var1 && ! $var2 ]]; then var2="something"; fi
Since that did not evaluate the way that I expected I wrote several other test cases and I am having a hard time understanding how they are being evaluated.
aa=true
bb=false
cc="python"
if [[ "$aa" ]]; then echo "Test0" ; fi
if [[ "$bb" ]]; then echo "Test0.1" ; fi
if [[ !"$aa" ]]; then echo "Test0.2" ; fi
if [[ ! "$aa" ]]; then echo "Test0.3" ; fi
if [[ "$aa" && ! "$bb" ]]; then echo "Test1" ; fi
if [[ "$aa" && ! "$aa" ]]; then echo "Test2" ; fi
if [[ "$aa" ]] && ! [[ "$bb" ]]; then echo "test3" ; fi
if [[ "$aa" ]] && ! [[ "$cc" ]]; then echo "test4" ; fi
if [[ $aa && ! $bb ]]; then echo "Test5" ; fi
if [[ $aa && ! $aa ]]; then echo "Test6" ; fi
if [[ $aa ]] && ! [[ $bb ]]; then echo "test7" ; fi
if [[ $aa ]] && ! [[ $cc ]]; then echo "test8" ; fi
When I run the preceding codeblock the only output I get is
Test0
Test0.1
Test0.2
however, my expectation is that I would get
Test0
Test1
Test3
Test5
Test7
I have tried to understand the best way to run similar tests, however most examples I have found are set up in the format of
if [[ "$aa" == true ]];
which is not quite what I want to do. So my question is what is the best way to make comparisons like this, and why do several of the test cases that I would expect to pass simply not?
Thank you!
Without any operators, [[ only checks if the variable is empty. If it is, then it is considered false, otherwise it is considered true. The contents of the variables do not matter.
Your understanding of booleans in shell context is incorrect.
var1=true
var2=false
Both the above variables are true since those are non-empty strings.
You could instead make use of arithmetic context:
$ a=1
$ b=0
$ ((a==1 && b==0)) && echo y
y
$ ((a==0 && b==0)) && echo y
$
$ ((a && !(b))) && echo y; # This seems to be analogous to what you were attempting
y
The shell does not have Boolean variables, per se. However, there are commands named true and false whose exit statuses are 0 and 1, respectively, and so can be used similarly to Boolean values.
var1=true
var2=false
if $var1 && ! $var2; then var2="something"; fi
The difference is that instead of testing if var1 is set to a true value, you expand it to the name of a command, which runs and succeeds. Likewise, var2 is expanded to a command name which runs and fails, but because it is prefixed with ! the exit status is inverted to indicate success.
(Note that unlike most programming languages, an exit status of 0 indicates success because while most commands have 1 way to succeed, there are many different ways they could fail, so different non-zero values can be assigned different meanings.)
true and false are evaluated as strings ;)
[[ $var ]] is an equivalent of [[ -n $var ]] that check if $var is empty or not.
Then, no need to quote your variables inside [[. See this reminder.
Finally, here is an explication of the difference between && inside brackets and outside.
The closest you can come seems to be use functions instead of variables because you can use their return status in conditionals.
$ var1() { return 0; }
$ var2() { return 1; } # !0 = failure ~ false
and we can test this way
$ var1 && echo "it's true" || echo "it's false"
it's true
$ var2 && echo "it's true" || echo "it's false"
it's false
or this way
$ if var1; then echo "it's true"; else echo "it's false"; fi
it's true
$ if var2; then echo "it's true"; else echo "it's false"; fi
it's false
Hope this helps.
Unfortunately i tried this and it doesn't work, i must use the [[ ]]
read input
for i in input
do
if [[ i = "$input" ]]
then
echo "i"
fi
done
when I run this nothing happens, it only reads my input
This line:
if [[ i = "$input" ]]
should be:
if [[ "$i" = "$input" ]]
OR:
if [[ "$i" == "$input" ]]
PS: Same thing for input also.
Remember that variables in shell are accessed with $ prefix.
May be you can re-factor your script to this:
read input
for i in $input
do
[[ "$i" == "something" ]] && echo "$i"
done
I think when you use only numbers you can also try:
for i in input
do
if [[ $i -eq "$input" ]]
then
echo "$i"
fi
done