I am executing my url through shell script and storing the response in a variable.
http://hostname.domain.com:8080/beat
After hitting the above url, I will be getting the below response which I need to parse it and extract value of state from it
num_retries_allowed: 3 count: 30 count_behind: 100 state: POST_INIT num_rounds: 60 hour_col: 2 day_col: 0
Now I am extracting value of state variable from the above string using grep.
#send the request, put response in variable
DATA=$(wget -O - -q -t 1 http://hostname.domain.com:8080/beat)
#grep $DATA for state
state=$(grep -oP 'state: \K\S+' <<< "$DATA")
[[ -z "$state" ]] && state=0
echo $state
Also if in $DATA variable state: string is not there by any chance, then I want to assign 0 to state variable. After that I want to verify the conditionals and exit out of the script depending on that.
If state is equal to POST_INIT then exit successfully out of the shell script or if state is equal to 0, then exit successfully as well.
if [[ $state -eq "POST_INIT" || $state -eq "0" ]]; then exit 0; fi
So my above if condition is not working somehow. Since what I have noticed is if my state variable value is IN_INIT, then also it is exiting out of the shell script? Is there anything wrong I am doing here in the string comparison?
-eq is for comparing numbers. = is for comparing strings.
If you were using [ instead of [[ you would be getting an error for a value of POST_INIT and IN_INIT.
$ state=POST_INIT
$ [ $state -eq 0 ]
-bash: [: POST_INIT: integer expression expected
$ echo $?
2
What I believe [[ is doing is actually being more clever and more annoying.
I believe it is expanding the variable and then using the expanded value in an arithmetic context (in which variables are expanded even from bare words) and since the variable POST_INIT doesn't have a value that gets expanded to 0 by default and your check passes.
$ state=POST_INIT
$ [[ $state -eq 0 ]]; echo $?
0
$ POST_INIT=5
$ [[ $state -eq 0 ]]; echo $?
1
$ POST_INIT=0
$ [[ $state -eq 0 ]]; echo $?
0
trying this
if [[ "$state" == "POST_INIT" || "$state" == "0" ]];
will help because if you use something like [ $state == "POST_INIT" ] , it ignores $state if it is null and would rather read the statement as [ == "POST_INIT". including " " ,prevents that case.
Related
How can I check if a variable is empty in Bash?
In Bash at least the following command tests if $var is empty:
if [[ -z "$var" ]]; then
# $var is empty, do what you want
fi
The command man test is your friend.
Presuming Bash:
var=""
if [ -n "$var" ]; then
echo "not empty"
else
echo "empty"
fi
I have also seen
if [ "x$variable" = "x" ]; then ...
which is obviously very robust and shell independent.
Also, there is a difference between "empty" and "unset". See How to tell if a string is not defined in a Bash shell script.
if [ ${foo:+1} ]
then
echo "yes"
fi
prints yes if the variable is set. ${foo:+1} will return 1 when the variable is set, otherwise it will return empty string.
[ "$variable" ] || echo empty
: ${variable="value_to_set_if_unset"}
if [[ "$variable" == "" ]] ...
The question asks how to check if a variable is an empty string and the best answers are already given for that.
But I landed here after a period passed programming in PHP, and I was actually searching for a check like the empty function in PHP working in a Bash shell.
After reading the answers I realized I was not thinking properly in Bash, but anyhow in that moment a function like empty in PHP would have been soooo handy in my Bash code.
As I think this can happen to others, I decided to convert the PHP empty function in Bash.
According to the PHP manual:
a variable is considered empty if it doesn't exist or if its value is one of the following:
"" (an empty string)
0 (0 as an integer)
0.0 (0 as a float)
"0" (0 as a string)
an empty array
a variable declared, but without a value
Of course the null and false cases cannot be converted in bash, so they are omitted.
function empty
{
local var="$1"
# Return true if:
# 1. var is a null string ("" as empty string)
# 2. a non set variable is passed
# 3. a declared variable or array but without a value is passed
# 4. an empty array is passed
if test -z "$var"
then
[[ $( echo "1" ) ]]
return
# Return true if var is zero (0 as an integer or "0" as a string)
elif [ "$var" == 0 2> /dev/null ]
then
[[ $( echo "1" ) ]]
return
# Return true if var is 0.0 (0 as a float)
elif [ "$var" == 0.0 2> /dev/null ]
then
[[ $( echo "1" ) ]]
return
fi
[[ $( echo "" ) ]]
}
Example of usage:
if empty "${var}"
then
echo "empty"
else
echo "not empty"
fi
Demo:
The following snippet:
#!/bin/bash
vars=(
""
0
0.0
"0"
1
"string"
" "
)
for (( i=0; i<${#vars[#]}; i++ ))
do
var="${vars[$i]}"
if empty "${var}"
then
what="empty"
else
what="not empty"
fi
echo "VAR \"$var\" is $what"
done
exit
outputs:
VAR "" is empty
VAR "0" is empty
VAR "0.0" is empty
VAR "0" is empty
VAR "1" is not empty
VAR "string" is not empty
VAR " " is not empty
Having said that in a Bash logic the checks on zero in this function can cause side problems imho, anyone using this function should evaluate this risk and maybe decide to cut those checks off leaving only the first one.
This will return true if a variable is unset or set to the empty string ("").
if [ -z "$MyVar" ]
then
echo "The variable MyVar has nothing in it."
elif ! [ -z "$MyVar" ]
then
echo "The variable MyVar has something in it."
fi
You may want to distinguish between unset variables and variables that are set and empty:
is_empty() {
local var_name="$1"
local var_value="${!var_name}"
if [[ -v "$var_name" ]]; then
if [[ -n "$var_value" ]]; then
echo "set and non-empty"
else
echo "set and empty"
fi
else
echo "unset"
fi
}
str="foo"
empty=""
is_empty str
is_empty empty
is_empty none
Result:
set and non-empty
set and empty
unset
BTW, I recommend using set -u which will cause an error when reading unset variables, this can save you from disasters such as
rm -rf $dir
You can read about this and other best practices for a "strict mode" here.
To check if variable v is not set
if [ "$v" == "" ]; then
echo "v not set"
fi
I'm trying to do a script that is used with two arguments - a file and an integer. It should check if the arguments are valid, otherwise exit with 1. Then it should either return 0 if the file is smaller than second argument, or echo size of the file to stdout. The script keeps returning value 123 instead of 1 or 0. Where is the problem? Thanks.
#!/bin/bash
if [ $# -eq 2 ];
then
if test $2 -eq $2 > /dev/null 2>&1
then
if [ -f $1 ];
then
if [ $(stat -c %s $1) -ge $2 ];
then
echo $(stat -c %s $1)
else
exit 0
fi
else
exit 1
fi
else
exit 1
fi
else
echo 042f9
exit 1
fi
I do not know where the "123" output comes from, but I would do it like this:
#!/bin/bash
# Must have 2 arguments
if [[ $# -ne 2 ]]
then
printf "042f9\n"
exit 1
fi
# File must exist
if [[ ! -f "$1" ]]
then
exit 1
fi
# File size > $2 check
filesize=$(stat -c %s "$1")
if [[ $filesize -ge $2 ]]
then
printf "%d" "$filesize"
else
exit 1
fi
A couple notes for your scripts (IMHO):
Like Mat mentioned in the comments, test 1 condition and exit right away. When I read your script, I had to go to the end to see what happens if the number of arguments is wrong. Logically there is nothing wrong with your code, it is just making it easier to read.
For bash, use [[ ]] to test if conditions.
I try never to call a function or command twice. That is why I stored the result of the stat command in a variable. If you use it more than once, store it, do not call the command again.
No need for ; since you put your then on the next line anyway.
Always double-quote your variables, especially if they are filenames. Weird filenames break so many scripts!
Finally use printf instead of echo. For simple cases, its the same, but echo does have some issues (https://unix.stackexchange.com/questions/65803/why-is-printf-better-than-echo).
Possible return values:
the size of the file, and the exit value is 0 ($?). The file is larger than argument 2 value.
"042f9", and the exit value is 1 ($?). Arguments error.
nothing, and the exit value is 1 ($?). Missing file error, or the file is smaller than argument 2 value.
I have a simple script in Bash to read a number in a file and then compare it with a different threshold. The output is this:
: integer expression expected
: integer expression expected
OK: 3
My code is this:
#!/bin/bash
wget=$(wget http://10.228.28.8/ -O /tmp/wget.txt 2>/dev/null)
output=$(cat /tmp/wget.txt | awk 'NR==6')
#output=7
echo $output
if [ $output -ge 11 ];then
echo "CRITICAL: $output"
exit 2
elif [ $output -ge 6 ] && [ $output -lt 11 ];then
echo "WARNING: $output"
exit 1
else
echo "OK: $output"
exit 0
fi
rm /tmp/wget.txt
I know what is the problem, I know that I'm reading a string and I try to compare a int. But I don't know how can I do to read this file and convert the number to read in a int var..
Any ideas?
The problem occurs when $output is the empty string; whether or not you quote the expansion (and you should), you'll get the integer expression required error. You need to handle the empty string explictly, with a default value of zero (or whatever default makes sense).
wget=$(wget http://10.228.28.8/ -O /tmp/wget.txt 2>/dev/null)
output=$(awk 'NR==6' < /tmp/get.txt)
output=${output:-0}
if [ "$output" -ge 11 ];then
echo "CRITICAL: $output"
exit 2
elif [ "$output" -ge 6 ];then
echo "WARNING: $output"
exit 1
else
echo "OK: $output"
exit 0
fi
(If you reach the elif, you already know the value of $output is less than 11; there's no need to check again.)
The problem also occurs, and is consistent with the error message, if output ends with a carriage return. You can remove that with
output=${output%$'\r'}
There are a couple of suggestions from my side regarding your code.
You could explicitly tell bash the output is an integer
declare -i output # See [1]
Change
output=$(cat /tmp/wget.txt | awk 'NR==6') # See [2]
may be better written as
output=$(awk 'NR==6' /tmp/wget.txt )
Change
if [ $output -ge 11 ]
to
if [ "0$output" -ge 11 ] # See [4]
or
if (( output >= 11 )) # Better See [3]
References
Check bash [ declare ].
Useless use of cat. Check [ this ]
Quoting [ this ] answer :
((...)) enable you to omit the dollar signs on integer and array variables and include spaces around operators for readability. Also empty variable automatically defaults to 0 in such a statement.
The zero in the beginning of "0$output" help you deal with empty $output
Interesting
Useless use of cat is a phrase that has been resounding in SO for long. Check [ this ]
[ #chepner ] has dealt with the empty output fiasco using [ bash parameter expansion ] in his [ answer ], worth having a look at.
A simplified script:
#!/bin/bash
wget=$(wget http://10.228.28.8/ -O /tmp/wget.txt 2>/dev/null)
output=$(awk 'NR==6' </tmp/wget.txt )
output="$(( 10#${output//[^0-9]} + 0 ))"
(( output >= 11 )) && { echo "CRITICAL: $output"; exit 2; }
(( output >= 6 )) && { echo "WARNING: $output"; exit 1; }
echo "OK: $output"
The key line to cleanup any input is:
output="$(( 10#${output//[^0-9]} + 0 ))"
${output//[^0-9]} Will leave only digits from 0 to 9 (will remove all non-numeric chars).
10#${output//[^0-9]} Will convert output to a base 10 number.
That will correctly convert numbers like 0019
"$(( 10#${output//[^0-9]} + 0 ))" Will produce a zero for a missing value.
Then the resulting number stored in output will be compared to limits and the corresponding output will be printed.
In BASH, It is a good idea to use double brackets for strings:
if [[ testing strings ]]; then
<whatever>
else
<whatever>
fi
Or double parenthesis for integers:
if (( testing ints )); then
<whatever>
else
<whatever>
fi
For example try this:
var1="foo bar"
if [ $var1 == 'foo bar' ]; then
echo "ok"
fi
Result:
$ bash: [: too many arguments
Now, this:
var2="foo bar"
if [[ $a == "foo bar" ]]; then
echo "ok"
fi
Result:
ok
For that, your code in BASH:
if [[ $output -ge 11 ]]; then
echo "CRITICAL: $output"
exit 2
elif [[ $output -ge 6 ]]; then
echo "WARNING: $output"
exit 1
else
echo "OK: $output"
exit 0
fi
I'm confused by the the value of "$?" in my shell script. I wrote a demo script as follows:
#!/bin/bash
echo "good"
if [ $? -ne 0 ];then
echo "$? not equal 0"
else
echo "$? equal 0"
fi
echo "good"
ret=$?
if [ $ret -ne 0 ];then
echo "$ret not equal 0"
else
echo "$ret equal 0"
fi
I know,"$?" is used to save the return value of the last function or command, but why is the output as below?
good
1 equal 0
good
0 equal 0
Does it mean that [ $? -eq 0 ] is also a command or function? I'm puzzled!
Your original code could be rewritten as:
$ if echo "good"; then echo "$? equal 0"; fi
good
0 equal 0
Since your code is only checking the exit value of the echo command, it's almost always going to return 0 (e.g. "true") unless its file descriptor is closed. For example:
$ echo foo; echo $?
foo
0
$ echo bar >&- ; echo $?
-bash: echo: write error: Bad file descriptor
1
I am trying to perform a variable swap where the user enters 2 different numbers and a check is performed to make sure that the second number "end" is bigger then the first number "start". If the starting number is bigger then the end number it will perform a swap so that the later calculations will work.
The error that I am getting is:
./Boot.sh: line 94: [: -ne: unary operator expected
if [ $end -gt $start ]
then
start=$swapper
end=$start
swapper=$end
fi
This is the full code as I seem to have made a few mistakes by the comments, I have just tried double brackets and am still having the same error.
{
counter=0
while :
do
if [ $counter -gt '0' ]
then
printf "\nWould you like to continue terminating processes?\n"
echo "Type 1 to contiue or 0 to exit"
read endProgram
if [ $endProgram -ne '1' ]
then
break
fi
fi
echo "Welcome to Max process killer"
while :
do
echo "Enter the first number of the process range"
read start
echo "Enter the last number of the process range"
read end
if [ $start -le '3' -o $end -le '3' ]
then
echo "Your first and last pid IDs must be geater then 3"
read -n 1
break
if [[ $end -gt $start ]]
then
start=$swapper
end=$start
swapper=$end
fi
fi
printf "\nAre you sure you would like to terminate these processes?\n"
echo "Enter 1 to confirm or 0 to cancel"
read confirm
if [ $read -ne '1' ]
then
break
fi
while [ $start -le $end ]
do
kill -9 "$start"
echo "Process ID:"$start "has been terminated"
start=$(( $start + 1 ))
done
break
done
counter=$(($counter + 1))
done
}
Your code:
read confirm
if [ $read -ne '1' ]
You read input to variable confirm and not to variable read. Variable read is empty and you get the error:
./Boot.sh: line 94: [: -ne: unary operator expected
Hint: Use a default value (e.g. 0) to avoid an empty variable:
if [ "${confirm:-0}" -ne '1' ]
From man bash:
${parameter:-word}: Use Default Values. If parameter is unset or null, the expansion of word is substituted. Otherwise, the value of parameter is substituted.
${parameter:=word}: Assign Default Values. If parameter is unset or null, the expansion of word is assigned to parameter. The value of parameter is then substituted. Positional parameters and special parameters may not be assigned to in this way.
Try using double brackets. They are generally safer. Here's a good wiki page comparing [[]] to [].
if [[ $end -gt $start ]]
then
swapper=$start
start=$end
end=$swapper
fi