using of arrays in loops

relikwie · 09-03-2009, 08:50 AM

Hi, need to process files within multiple directories and transfer these to a remote server. What I had in mind was to use arrays for this; code pasted below (explains it better):

Code:

#set the arrays
array_A=( fileA* pathtodestA hostA passwordA )
array_B=( fileB* pathtodestB hostB passwordB )
array_c=( fileC* pathtodestC hostC passwordC )

# set variables within the loop with elements from each array at the time
# and call an ftp function with the variables as arguments
for arrays in array_A array_B array_C ; do

# this is where I get stuck
file=${arrays[0]} 
path=${arrays[1]} 
host=${arrays[2]}
user=${arrays[3]}
pass=${arrays[3]}

# call ftp function
transfer_func $file $path $host $user $pass

So actually handle each array at a time.

I'am fairly new to this and guess my approach doesn't make any sense at all.

Hope someone can help me with this?

regards, relikwie

David the H. · 09-03-2009, 11:12 AM

AFAIK, you can't directly use variables inside the names of other variables. You have to use indirect methods, such as "eval" to create them.

I don't know if this is a "proper" way to do it, but it does seem to work:

Code:

#!/bin/bash

array_A=( fileA* pathtodestA hostA passwordA )
array_B=( fileB* pathtodestB hostB passwordB )
array_C=( fileC* pathtodestC hostC passwordC )


for x in A B C ; do

x='${array_'${x}

eval file="${x}[0]}"
eval path="${x}[1]}"
eval host="${x}[2]}"
eval user="${x}[3]}"
eval pass="${x}[3]}"

echo
echo array = "${x}}"
echo
echo "file = $file"
echo "path = $path"
echo "host = $host"
echo "user = $user"
echo "password = $pass"

done

There are probably better ways to go about it, perhaps with indirect variable referencing.

PS: please be careful about posting multiple threads. Ask the moderators to delete any duplicates (use the report button).

David the H. · 09-03-2009, 11:40 AM

By the way, even better, if possible, would be to move the setting of the array to inside the loop along with the rest of it. Then you'd only need to use one array at a time. If the each input is a line in a file, for example:

Code:

while read inputstring ; do

array=( $(echo $inputstring)  ) 

file=${array[0]} 
path=${array[1]} 
host=${array[2]}
user=${array[3]}
pass=${array[3]}

done <inputfile.txt

catkin · 09-03-2009, 12:26 PM

This thread is a duplicate of scripting-strings-752102

relikwie · 09-04-2009, 03:43 AM

Hi guys, thanks for the replies.

I wasn't aware of any doublepost, must have happened while hitting the back and forward button of my browser. sorry about that.

catkin, I have tried using your version which should look like this:

Code:

#set the arrays

files=( file1,     file2,     file3 )
paths=( path1,     path2,     path3 )
hosts=( host1,     host2,     host3 )
passwords=( password1,  password2,      password3 )
index_max=3


for (( index=1; index >= 3; index++ ))
do
    echo  ${files[$index]} ${paths[$index]} ${hosts[$index]} ${users[$index]} ${passwords[$index]}
done

for some reason it doesn't work. i'll go and try to grasp what you guys have put up. and hopefully I can figure this out on my own

it's appreciated!

colucix · 09-04-2009, 04:15 AM

Quote:

Originally Posted by relikwie

for some reason it doesn't work. i'll go and try to grasp what you guys have put up. and hopefully I can figure this out on my own

Some (maybe) useful notes:
1. arrays in bash are 0-based
2. array's element separator in array assignment is $IFS, not comma
3. also there is an error in the C-style for-loop definition.
Maybe this works (check the differences to see the flaws):

Code:

#!/bin/bash
files=( file1     file2     file3 )
paths=( path1     path2     path3 )
hosts=( host1     host2     host3 )
passwords=( password1  password2      password3 )

for (( index=0; index <= 2; index++ ))
do
    echo  ${files[$index]} ${paths[$index]} ${hosts[$index]} ${users[$index]} ${passwords[$index]}
done

catkin · 09-04-2009, 05:29 AM

Quote:

Originally Posted by colucix

Some (maybe) useful notes:
1. arrays in bash are 0-based
2. array's element separator in array assignment is $IFS, not comma
3. also there is an error in the C-style for-loop definition.
Maybe this works (check the differences to see the flaws):

Code:

#!/bin/bash
files=( file1     file2     file3 )
paths=( path1     path2     path3 )
hosts=( host1     host2     host3 )
passwords=( password1  password2      password3 )

for (( index=0; index <= 2; index++ ))
do
    echo  ${files[$index]} ${paths[$index]} ${hosts[$index]} ${users[$index]} ${passwords[$index]}
done

Oops

Thanks for correcting my errors, colucix

Test, test, test!

konsolebox · 09-05-2009, 01:57 AM

colucix and catkin have already made the proper explanations but just in case this will also help...

# list.txt

Code:

"fileA" "pathtodestA" "hostA" "userA" "passwordA"
"fileB" "pathtodestB" "hostB" "userB" "passwordB"
"fileC" "pathtodestC" "hostC" "userC" "passwordC"

# script.sh

Code:

IFS=$' \t\n'  # normal IFS

while read -u 4 LINE; do
    # these are just optional.  you can directly access the variables if you want

    set -- $LINE  # or eval "set -- $LINE"
    file=$1 path=$2 host=$3 user=$4 pass=$5

    # or

    array=($LINE)
    file=${array[0]} path=${array[1]} host=${array[2]} user=${array[3]} pass=${array[4]}

    # do the work here
    : ...

    # optionally ask user for an input before continuing to the next
    : echo press any key to continue
    : read -n1  # please check if -n1 is the proper option
done 4< list.txt

ta0kira · 09-05-2009, 11:56 AM

In cases like this, I find I can usually pipe lines to a loop and cut them, which is almost always straight-forward and easily reproducible:

Code:

specs_A='fileA*,pathtodestA,hostA,passwordA'
specs_B='fileB*,pathtodestB,hostB,passwordB'
specs_C='fileC*,pathtodestC,hostC,passwordC'

{ echo "$specs_A";
  echo "$specs_B";
  echo "$specs_C"; } | while read line; do

  file="$( echo "$line" | cut -d, -f1 )"
  path="$( echo "$line" | cut -d, -f2 )"
  host="$( echo "$line" | cut -d, -f3 )"
  user="$( echo "$line" | cut -d, -f4 )"
  pass="$( echo "$line" | cut -d, -f5 )"

  transfer_func $file $path $host $user $pass
done

This at least makes the loop independent of the source, e.g. you could just as easily put your transfers in a CSV and cat it into the loop.
Kevin Barry