The script I'm writing will require me to pass some command line parameters. I would like to use these parameters within an array, but I'm not sure how.
A very basic example of this would be (script run as ./script.sh array1):
#!/bin/bash
array1=( a b c d )
echo ${#$1[#]}
The output should be 4, but I receive the following error:
line 5: ${#$1[#]}: bad substitution.
I don't have to use arrays, but would like to.
Thanks for any ideas
you need to get bash to substitute the value of $1 before evaluating the line, try this...
eval echo \${#$1[#]}
eval echo '${#'$1'[#]};'
Related
This question already has answers here:
Dynamic variable names in Bash
(19 answers)
Closed 6 years ago.
I want to declare a variable, the name of which comes from the value of another variable, and I wrote the following piece of code:
a="bbb"
$a="ccc"
but it didn't work. What's the right way to get this job done?
eval is used for this, but if you do it naively, there are going to be nasty escaping issues. This sort of thing is generally safe:
name_of_variable=abc
eval $name_of_variable="simpleword" # abc set to simpleword
This breaks:
eval $name_of_variable="word splitting occurs"
The fix:
eval $name_of_variable="\"word splitting occurs\"" # not anymore
The ultimate fix: put the text you want to assign into a variable. Let's call it safevariable. Then you can do this:
eval $name_of_variable=\$safevariable # note escaped dollar sign
Escaping the dollar sign solves all escape issues. The dollar sign survives verbatim into the eval function, which will effectively perform this:
eval 'abc=$safevariable' # dollar sign now comes to life inside eval!
And of course this assignment is immune to everything. safevariable can contain *, spaces, $, etc. (The caveat being that we're assuming name_of_variable contains nothing but a valid variable name, and one we are free to use: not something special.)
You can use declare and !, like this:
John="nice guy"
programmer=John
echo ${!programmer} # echos nice guy
Second example:
programmer=Ines
declare $programmer="nice gal"
echo $Ines # echos nice gal
This might work for you:
foo=bar
declare $foo=baz
echo $bar
baz
or this:
foo=bar
read $foo <<<"baz"
echo $bar
baz
You could make use of eval for this.
Example:
$ a="bbb"
$ eval $a="ccc"
$ echo $bbb
ccc
Hope this helps!
If you want to get the value of the variable instead of setting it you can do this
var_name1="var_name2"
var_name2=value_you_want
eval temp_var=\$$var_name1
echo "$temp_var"
You can read about it here indirect references.
You can assign a value to a variable using simple assignment using a value from another variable like so:
#!/usr/bin/bash
#variable one
a="one"
echo "Variable a is $a"
#variable two with a's variable
b="$a"
echo "Variable b is $b"
#change a
a="two"
echo "Variable a is $a"
echo "Variable b is $b"
The output of that is this:
Variable a is one
Variable b is one
Variable a is two
Variable b is one
So just be sure to assign it like this b="$a" and you should be good.
I'm stucked on a bash script.
I'm having a config.ini files like this :
#Username
username=user
#Userpassword
userpassword=password
And i'm looking in a bash script to extract this information and put it in a associative array. My script looks like :
declare -A array
OIFS=$IFS
IFS='='
grep -vE '^(\s*$|#)' file | while read -r var1 var2
do
array+=([$var1]=$var2)
done
echo ${array[#]}
But the array seems to be empty because the commande echo ${array[#]} gives no output.
Any idea why me script don't work ? Thanks for your help and sorry for my bad english.
Common error - "grep | while" causes the while loop to be executed in a separate shell and the variables inside the loop are not global to your shell. Use a here string instead:
while read -r var1 var2
do
array+=([$var1]=$var2)
done <<< $(grep -vE '^(\s*$|#)' file)
Assuming the file can be trusted (ie the content is regulated and known), the simplest method would be to source the ini file and then directly use the variable names within the script:
. config.ini
You can either use the period (.) as above or the source builtin command
I try to transfer the excellent example docker-haproxy from centos to alpine.
A shell script is used to process a list of values given as parameters to the script into an array, then write these values plus their index to some file.
The following construction works in bash:
ServerArray=${SERVERS:=$1}
...
for i in ${ServerArray[#]}
do
echo " " server SERVER_$COUNT $i >> /haproxy/haproxy.cfg
let "COUNT += 1"
done
but not in ash (or sh):
syntax error: bad substitution
The error refers to line
for i in ${ServerArray[#]}
What is the correct syntax here? I guess the line
ServerArray=${SERVERS:=$1}
does not define an array as intended, but googling for long did not help me.
bash to sh (ash) spoofing says
sh apparently has no arrays.
If so, how to solve the problem then?
I guess I can do with this construction:
#!/bin/sh
# test.sh
while [ $# -gt 0 ]
do
echo $1
shift
done
delivers
/ # ./test 172.17.0.2:3306 172.17.0.3:3306
172.17.0.2:3306
172.17.0.3:3306
which is what I need to proceed
I crawled through lots of boards but didn't find the final solution for my problem.
I have got an array, named "array0", the name is stored to a variable called arrayname. Also I've got a logged IP address, let's say 127.0.0.1, also stored in a variable, called ip.
Now I want to assign the IP to index 3 in the array like that:
"$arrayname"[3]="$ip"
So, this didn't work. I tried lots of ways how to solve that but none worked.
Is anyone out there who can tell me the final solution for this case?
Update: The given opportunities to handle the problem are great! But I forgot to mention that the array I'm working with is just sourced from another file (also written in bash). My goal is now to edit the array in the sourced file itself. Any more ideas for that?
Try
read ${arrayname}[3] <<<"$ip"
You'll need to use the declare command and indirect parameter expansion, but it's a little tricky to use with array names. It helps if you think of the index as part of the variable name, instead of an operator applied to the array name, like in most languages.
array0=(1 2 3 4 5)
arrayname=array0
name=$arrayname[3]
declare "$name=$ip"
echo "${!name}
And yet another way to do it, this time using the versatile printf.
printf -v "$arrayname[3]" %s "$ip"
demo
#!/bin/bash
array0=(a b c d e)
echo "${array0[#]}"
arrayname='array0'
ip='127.0.0.1'
printf -v "$arrayname[3]" %s "$ip"
echo "${array0[#]}"
output
a b c d e
a b c 127.0.0.1 e
See this:
# declare -a arrayname=(element1 element2 element3)
# echo ${arrayname[0]}
element1
# arrayname[4]="Yellow"
# echo ${arrayname[4]}
Yellow
# export ip="192.168.190.23"
# arrayname[5]=$ip
# echo ${arrayname[5]}
192.168.190.23
You don't have to use quotes.
After initializing the arrays, you can access the array elements using their indices as follows.
Access as:
${arrayname[3]}
Noble StackOverflow readers,
I have a comma seperated file, each line of which I am putting into an array.
Data looks as so...
25455410,GROU,AJAXa,GROU1435804437
25455410,AING,EXS3d,AING4746464646
25455413,TRAD,DLGl,TRAD7176202067
There are 103 lines and I am able to generate the 103 arrays without issue.
n=1; while read -r OrdLine; do
IFS=',' read -a OrdLineArr${n} <<< "$OrdLine"
let n++
done < $WkOrdsFile
HOWEVER, I can only access the arrays as so...
echo "${OrdLineArr3[0]} <---Gives 25455413
I cannot access it with the number 1-103 as a variable - for example the following doesn't work...
i=3
echo "${OrdLineArr${i}[0]}
That results in...
./script2.sh: line 24: ${OrdLineArr${i}[0]}: bad substitution
I think that the answer might involve 'eval' but I cannot seem to find a fitting example to borrow. If somebody can fix this then the above code makes for a very easy to handle 2d array replacement in bash!
Thanks so much for you help in advance!
Dan
You can use indirect expansion. For example, if $key is OrdLineArr4[7], then ${!key} (with an exclamation point) means ${OrdLineArr4[7]}. (See ยง3.5.3 "Shell Parameter Expansion" in the Bash Reference Manual, though admittedly that passage doesn't really explain how indirect expansion interacts with arrays.)
I'd recommend wrapping this in a function:
function OrdLineArr () {
local -i i="$1" # line number (1-103)
local -i j="$2" # field number (0-3)
local key="OrdLineArr$i[$j]"
echo "${!key}"
}
Then you can write:
echo "$(OrdLineArr 3 0)" # prints 25455413
i=3
echo "$(OrdLineArr $i 0)" # prints 25455413
This obviously isn't a total replacement for two-dimensional arrays, but it will accomplish what you need. Without using eval.
eval is usually a bad idea, but you can do it with:
eval echo "\${OrdLineArr$i[0]}"
I would store each line in an array, but split it on demand:
readarray OrdLineArr < $WkOrdsFile
...
OrdLine=${OrdLineArr[i]}
IFS=, read -a Ord <<< "$OrdLine"
However, bash isn't really equipped for data processing; it's designed to facilitate process and file management. You should consider using a different language.