When I execute below script it works fine:
if [[ "[1,2,3]" =~ .*1.* ]]; then
techStatus=1
else
techStatus=0;
fi
echo $techStatus
Output is 1
But when we changes it to variable it does not work.
var1=[1,2,3]
var2=1
if [[ "$var1" =~ .*"$var2".* ]]; then
techStatus=1
else
techStatus=0;
fi
echo $techStatus
Output is 0.
Please help me figure out what is wrong here.
A better & readable approach would be to convert var1 to array and loop through var1.
var1=(1 2 3)
var2=1
for elem in "${var1[#]}"; do
if [[ "$elem" -eq "$var2" ]]; then
techStatus=1
break
else
techStatus=0
fi
done
echo "$techStatus"
Related
$var=1545334345
The $var is dynamic. How do I check if it starts with 15? I tried:
if [[ $var == 15* ]]; then
echo "Yes"
fi
and
if (( $var -eq 15* )); then
echo "Yes"
fi
Neither works.
Remove the $ from the assignment.
var=1545334345
The first if statement you wrote is correct.
if [[ $var == 15* ]]; then
echo "Yes"
fi
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.
I want an if/then statement in Bash and I can't seem to get it to work. I would like to say "If the line begins with > character, then do this, else do something else".
I have:
while IFS= read -r line
do
if [[$line == ">"*]]
then
echo $line'first'
else
echo $line'second'
fi
done
But it isn't working.
I also tried to escape the ">" by saying:
if [[$line == ^\>*]]
Which didn't work either.
Both ways I am getting this error:
line 27: [[>blah: command not found
Suggestions?
Spaces are needed inside [[ and ]] as follows:
if [[ "$line" == ">"* ]]; then
echo "found"
else
echo "not found"
fi
This attempt attempt uses a regex:
line="> line"
if [[ $line =~ ^\> ]] ; then
echo "found"
else
echo "not found"
fi
This one uses a glob pattern:
line="> line"
if [[ $line == \>* ]] ; then
echo "found"
else
echo "not found"
fi
Spacing is important.
$ [[ ">test" == ">"* ]]; echo $?
0
$ [[ "test" == ">"* ]]; echo $?
1
if grep -q '>' <<<$line; then
..
else
..
fi
using grep is much better :)
I try to test if a string starts with a certain prefix. But my script seems not work (I would expect the "if" branch will not get run). Can some Bash expert help to take a look? thanks!
Here is my code and test result:
$ cat testb.bash
#!/bin/bash
my_var="abcdefg";
if [[ "${my_var:0:5}"=="order" ]]; then
echo "value of my_var is ${my_var}.";
fi;
if [[ "${my_var:0:5}" -eq "order" ]]; then
echo "value of my_var is ${my_var}.";
fi;
if [ "${my_var:0:5}"="order" ]; then
echo "value of my_var is ${my_var}.";
fi;
$ bash -x testb.bash
+ my_var=abcdefg
+ [[ -n abcde==order ]]
+ echo 'value of my_var is abcdefg.'
value of my_var is abcdefg.
+ [[ abcde -eq order ]]
+ echo 'value of my_var is abcdefg.'
value of my_var is abcdefg.
+ '[' abcde=order ']'
+ echo 'value of my_var is abcdefg.'
value of my_var is abcdefg.
$
Whitespace is significant in this case. As you can see in the -x output, it understands the first condition as
[[ -n "${my_var:0:5}==order" ]]
Moreover, to test for a prefix, you can use a pattern:
[[ $my_var == order* ]]
To test the existence of substring, you can use either of these:
if [[ "$j" =~ string1 ]]; then
if [[ $j == *string1* ]]; then
In your particular case, you miss a space surounding ==, so instead of
if [[ "${my_var:0:5}"=="order" ]]; then
it should be
if [[ "${my_var:0:5}" == "order" ]]; then
^ ^
Finally, note that your condition was evaluated as true because it was evaluating if [ "string" ], which is true if string is not empty:
$ [ "a" ] && echo "yes"
yes
Test
$ cat a
#!/bin/bash
my_var="abcdefg";
if [[ "${my_var:0:5}" == "order" ]]; then
echo "value of my_var is ${my_var}."
elif [[ "${my_var:0:5}" == "abcde" ]]; then
echo "yeahaa"
else
echo "is not"
fi
$ ./a
yeahaa
Ok, i tested your code, you shoud such as the following code:
prefix="pre_order";
pre="pre_"
len=${#pre}
echo $len
if [[ "${prefix:0:len}" == "blahvlah" ]] ; then
echo "dddd"
fi;
Notes:
use == for string comparation
for ${} you should initilize a string variable before ${}
use len=${#pre} for lenght of string.
A POSIX-compliant way to test for a prefix is to attempt to remove the prefix, and compare the result to the original string. If the two are the same, the prefix is not present, the removal fails, and the expression expands to the original string.
prefix=foo
string=foobar
if [ "${string#$prefix}" = "$string" ]; then
printf "$string does not start with $prefix\n"
else
printf "$string starts with $prefix\n"
fi
if [[ $line == *"option 1"* ]]
then
CURRENT_OPTION=1
fi
if [[ $line == *"option 2"* ]]
then
CURRENT_OPTION=2
fi
if [[ $line =~ "What i want" ]]
then
if [[ $CURRENT_OPTION -eq 1 ]]
then
MEM1=$(awk '/Used heap/ { gsub(/M/, " "); print $4 }')
elif [[ $CURRENT_OPTION -eq 2 ]]
then
MEM2=$(awk '/Used heap/ { gsub(/M/, " "); print $4 }')
fi
fi
Because CURRENT_OPTION is defined within an if, its value is not correct when checked in the third if. How do I pass it out so that it is?
Just declare CURRENT_OPTION at the top, something like:
declare -i CURRENT_OPTION=0
i to declare it as an int.
In all of your if statements you should enclose the variables in double quotes. If the variable is an empty string (or if the variable doesn't exist) then the if statement will not contain enough arguments and will throw an error.
Here is an example:
if [[ $var -eq 1 ]]
then
echo yes
else
echo no
fi
If var is uninitialised, bash will expand the statement to look like this:
if [[ -eq 1 ]]
then
echo yes
else
echo no
fi
There are not enough arguments to make the if statement valid here, and bash will throw an error:
bash: conditional binary operator expected
bash: syntax error near `1'
By wrapping the variable in quotes, this situation is avoided. This statement:
if [[ "$var" -eq 1 ]]
...
is expanded to:
if [[ "" -eq 1 ]]
...
and now the if statement has enough arguments (the first one being an empty string) to parse.