Would like to read multiple values from a property file using a shell script
My properties files looks something like below, the reason I added it following way was to make sure, if in future more students joins I just need to add in in the properties file without changing any thing in the shell script.
student.properties
total_student=6
student_name_1="aaaa"
student_name_2="bbbb"
student_name_3="cccc"
student_name_4="dddd"
student_name_5="eeee"
When I run below script I not getting the desired output, for reading the student names from properties file
student.sh
#!/bin/bash
. /student.properties
i=1
while [ $i -lt $total_student ]
do
{
std_Name=$student_name_$i
echo $std_Name
#****** my logic *******
} || {
echo "ERROR..."
}
i=`expr $i + 1`
done
Output is something like this
1
2
3
4
5
I understand the script is not getting anything for $student_name_ hence only $i value is getting printed.
Hence, wanted to know how to read values from the properties file.
You can do variable name interpolation with ${!foo}. If $foo is "bar", then ${!foo} gives you the value of $bar. In your code that means changing
std_Name=$student_name_$i
to
var=student_name_$i
std_Name=${!var}
Alternatively, you could store the names in an array. Then you wouldn't have to do any parsing.
student.properties
student_names=("aaaa" "bbbb" "cccc" "dddd" "eeee")
student.sh
#!/bin/bash
. /student.properties
for student_name in "${student_names[#]}"; do
...
done
You can use indirect expansion:
std_Name=student_name_$i
echo "${!std_Name}"
the expression ${!var} basically evaluates the variable twice:
first evaluation: student_name_1
second evaluation: foo
Note that this is rarely a good idea and that using an array is almost always preferred.
Related
I'm wondering if anyone can help. I've not managed to find much in the way of examples and I'm not sure where to start coding wise either.
I have a file with the following contents...
VarA=/path/to/a
VarB=/path/to/b
VarC=/path/to/c
VarD=description of program
...
The columns are delimited by the '=' and some of the items in the 2nd column may contain gaps as they aren't just paths.
Ideally I'd love to open this in my script once and store the first column as the variable and the second as the value, for example...
echo $VarA
...
/path/to/a
echo $VarB
...
/path/to/a
Is this possible or am I living in a fairy land?
Thanks
You might be able to use the following loop:
while IFS== read -r name value; do
declare "$name=$value"
done < file.txt
Note, though, that a line like foo="3 5" would include the quotes in the value of the variable foo.
A minus sign or a special character isn't allowed in a variable name in Unix.
You may consider using BASH associative array for storing key and value together:
# declare an associative array
declare -A arr
# read file and populate the associative array
while IFS== read -r k v; do
arr["$k"]="$v"
done < file
# check output of our array
declare -p arr
declare -A arr='([VarA]="/path/to/a" [VarC]="/path/to/c" [VarB]="/path/to/b" [VarD]="description of program" )'
What about source my-file? It won't work with spaces though, but will work for what you've shared. This is an example:
reut#reut-home:~$ cat src
test=123
test2=abc/def
reut#reut-home:~$ echo $test $test2
reut#reut-home:~$ source src
reut#reut-home:~$ echo $test $test2
123 abc/def
I am writing a bash script to loop through all the directories and rename the directory to the value of the array, but it seems my (i th) value is not incrementing correctly and it also says "(i th) command not found" when I run my bash script.
Here is my code: I replaced the values inside Unix with place holder values.
#!/bin/bash
declare -a Unix=(value1 value2 value3 .... );
i = 0
for d in */; do
echo ${Unix[$i]}
#mv $d ${Unix[$i]}
(($i+1))
done
You are doing two things wrong. Firstly , to answer your problem,
(($i+1))
should be
(($i+=1))
also, you should remove the spaces in the line
i = 0
so it looks like
i=0
Firstly, you might want to quote your directory names in the mv command, or you get into trouble with names containing spaces:
mv "$d" "${Unix[i]}"
As you see, it's not necessary to prepend the i in the index with $, as [] is an "arithmetic context" here and expands variable names.
Secondly, your increment does nothing: you just add 1 to i and throw the result away. You can use the increment operator instead:
(( ++i ))
Again, the $ is not needed.
I want to run a shell script that can simultaneously loop through two variables.
So that I can have an input and output file name. I feel like this isn't too hard of a concept but any help is appreciated.
Files = "File1,
File2,
...
FileN
"
Output = OutFile1,
Outfile2,
...
OutfileN
"
and I would in theory my code would be:
for File in $Files
do
COMMAND --file $File --ouput $Output
done
Obviously, there needs to be another loop but I'm stuck, any help is appreciated.
You don't really need to loop 2 variables, just use 2 BASH arrays:
input=("File1" "File2" "File3")
output=("OutFile1" "OutFile2" "OutFile3")
for ((i=0; i<${#input[#]}; i++)); do
echo "Processing input=${input[$i]} and output=${output[$i]}"
done
zsh enables multiple loop variables before the list.
#!/bin/zsh
input2output=(
'File1' 'Outfile1'
'File2' 'Outfile2'
)
for input ouput in $input2output
do
echo "[$input] --> [$ouput]"
done
quotes from zsh(5.9) manual or man zshmisc
for name ... [ in word ... ] term do list done
More than one parameter name can appear before the list of words. If N names are given, then on each execution of the loop the next N words are assigned to the corresponding parameters. If there are more names than remaining words, the remaining parameters are each set to the empty string.
Need to save content of nm function into variable. Files, which nm should run are arguments of script.
Currently I have:
while [ $i -le $#]
do
eval nm "\$$i"
i=$(( i+1 ))
done
which list me nm result of each file.
But I need to save result of nm file into variable.
I tried
eval CONTENT=$(nm "\$$i")
but this show me error "nm: '$1': No such file."
#devnull has solved your immediate problem (in his comment), but I suggest you rewrite your loop as follows:
for f
do
CONTENT=$(nm "$f")
# ... work with $CONTENT
done
A for loop without in ... implicitly loops over all arguments passed to the script.
Since f will then directly contain the value of each argument, there is no need to use eval.
(As an aside, your original code won't run as posted, because the [ ... ] conditional will break for 2 reasons: (a) $i is not initialized and (b) the closing ] must have a space before it.)
"eval" is part of the command you need to redirect:
CONTENT=$(eval nm "\$$i")
You will have to set up an array to store results tho:
CONTENT[$i]=$(eval nm "$\$$i")
After thoroughly searching for a way to create an associative array in bash, I found that declare -A array will do the trick. But the problem is, it is only for bash version 4 and the bash version the server has in our system is 3.2.16.
How can I achieve some sort of associative array-like hack in bash 3? The values will be passed to a script like
ARG=array[key];
./script.sh ${ARG}
EDIT: I know that I can do this in awk, or other tools but strict bash is needed for the scenario I am trying to solve.
Bash 3 has no associative arrays, so you're going to have to use some other language feature(s) for your purpose. Note that even under bash 4, the code you wrote doesn't do what you claim it does: ./script.sh ${ARG} does not pass the associative array to the child script, because ${ARG} expands to nothing when ARG is an associative array. You cannot pass an associative array to a child process, you need to encode it anyway.
You need to define some argument passing protocol between the parent script and the child script. A common one is to pass arguments in the form key=value. This assumes that the character = does not appear in keys.
You also need to figure out how to represent the associative array in the parent script and in the child script. They need not use the same representation.
A common method to represent an associative array is to use separate variables for each element, with a common naming prefix. This requires that the key name only consists of ASCII letters (of either case), digits and underscores. For example, instead of ${myarray[key]}, write ${myarray__key}. If the key is determined at run time, you need a round of expansion first: instead of ${myarray[$key]}, write
n=myarray__${key}; echo ${!n}
For an assignment, use printf -v. Note the %s format to printf to use the specified value. Do not write printf -v "myarray__${key}" %s "$value" since that would treat $value as a format and perform printf % expansion on it.
printf -v "myarray__${key}" %s "$value"
If you need to pass an associative array represented like this to a child process with the key=value argument representation, you can use ${!myarray__*} to enumerate over all the variables whose name begins with myarray__.
args=()
for k in ${!myarray__*}; do
n=$k
args+=("$k=${!n}")
done
In the child process, to convert arguments of the form key=value to separate variables with a prefix:
for x; do
if [[ $x != *=* ]]; then echo 1>&2 "KEY=VALUE expected, but got $x"; exit 120; fi
printf -v "myarray__${x%%=*}" %s "${x#*=}"
done
By the way, are you sure that this is what you need? Instead of calling a bash script from another bash script, you might want to run the child script in a subshell instead. That way it would inherit from all the variables of the parent.
Here is another post/explanation on associative arrays in bash 3 and older using parameter expansion:
https://stackoverflow.com/a/4444841
Gilles' method has a nice if statement to catch delimiter issues, sanitize oddball input ...etc. Use that.
If you are somewhat familiar with parameter expansion:
http://www.gnu.org/software/bash/manual/html_node/Shell-Parameter-Expansion.html
To use in your scenario [ as stated: sending to script ]:
Script 1:
sending_array.sh
# A pretend Python dictionary with bash 3
ARRAY=( "cow:moo"
"dinosaur:roar"
"bird:chirp"
"bash:rock" )
bash ./receive_arr.sh "${ARRAY[#]}"
Script 2: receive_arr.sh
argAry1=("$#")
function process_arr () {
declare -a hash=("${!1}")
for animal in "${hash[#]}"; do
echo "Key: ${animal%%:*}"
echo "Value: ${animal#*:}"
done
}
process_arr argAry1[#]
exit 0
Method 2, sourcing the second script:
Script 1:
sending_array.sh
source ./receive_arr.sh
# A pretend Python dictionary with bash 3
ARRAY=( "cow:moo"
"dinosaur:roar"
"bird:chirp"
"bash:rock" )
process_arr ARRAY[#]
Script 2: receive_arr.sh
function process_arr () {
declare -a hash=("${!1}")
for animal in "${hash[#]}"; do
echo "Key: ${animal%%:*}"
echo "Value: ${animal#*:}"
done
}
References:
Passing arrays as parameters in bash
If you don't want to handle a lot of variables, or keys are simply invalid variable identifiers, and your array is guaranteed to have less than 256 items, you can abuse function return values. This solution does not require any subshell as the value is readily available as a variable, nor any iteration so that performance screams. Also it's very readable, almost like the Bash 4 version.
Here's the most basic version:
hash_index() {
case $1 in
'foo') return 0;;
'bar') return 1;;
'baz') return 2;;
esac
}
hash_vals=("foo_val"
"bar_val"
"baz_val");
hash_index "foo"
echo ${hash_vals[$?]}
More details and variants in this answer
You can write the key-value pairs to a file and then grep by key. If you use a pattern like
key=value
then you can egrep for ^key= which makes this pretty safe.
To "overwrite" a value, just append the new value at the end of the file and use tail -1 to get just the last result of egrep
Alternatively, you can put this information into a normal array using key=value as value for the array and then iterator over the array to find the value.
This turns out to be ridiculously easy. I had to convert a bash 4 script that used a bunch of associative arrays to bash 3. These two helper functions did it all:
array_exp() {
exp=${#//[/__}
eval "${exp//]}"
}
array_clear() {
unset $(array_exp "echo \${!$1__*}")
}
I'm flabbergasted that this actually works, but that's the beauty of bash.
E.g.
((all[ping_lo] += counts[ping_lo]))
becomes
array_exp '((all[ping_lo] += counts[ping_lo]))'
Or this print statement:
printf "%3d" ${counts[ping_lo]} >> $return
becomes
array_exp 'printf "%3d" ${counts[ping_lo]}' >> $return
The only syntax that changes is clearing. This:
counts=()
becomes
array_clear counts
and you're set. You could easily tell array_exp to recognize expressions like "=()" and handle them by rewriting them as array_clear expressions, but I prefer the simplicity of the above two functions.