Bash – Generate random number after value in bash

bashrandomshell-script

I want my machine to automatically download some files. That doesn't have to be very efficient. So I decided to do this with a bash script.

It works so far when I encode the URL hardly. But I want to get the files retrieved in irregular order and I thought I would use simple variables. How do I get the random number into my variable?

My approach 

data_link0="https://example.com/target1.html"
data_link1="https://example.com/target2.html"
data_link2="https://example.com/target3.html"
data_link3="https://example.com/target4.html"

useragent0="Mozilla/5.0 (iPhone; CPU iPhone OS 10_0_1 like Mac OS X) AppleWebKit/602.1.50 (KHTML, like Gecko) Version/10.0 Mobile/14A403 Safari/602.1"
useragent1="Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_3) AppleWebKit/604.5.6 (KHTML, like Gecko) Version/11.0.3 Safari/604.5.6"
useragent3="Mozilla/5.0 (Windows 7; ) Gecko/geckotrail Firefox/firefoxversion"

wget --user-agent="$user_agent[$((RANDOM % 3))]" "$datei_link$((RANDOM % 3))"

unfortunately does not work.

Best Answer

As far as you need to retrieve all the urls, a better way would be using (GNU/linux coreutils) (or sort -R coreutils too):

shuf file | xargs wget

File :

$ cat file
"https://example.com/target1.html"
"https://example.com/target2.html"
"https://example.com/target3.html"
"https://example.com/target4.html"

man 1 shuf

NAME

shuf - generate random permutations

New comments, new needs, new code :

(requiring random user-agent)

$ cat uas
Mozilla/5.0 (X11; Linux x86_64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/28.0.1500.52 Safari/537.36
Mozilla/5.0 (Windows NT 6.1; WOW64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/28.0.1500.52 Safari/537.36 OPR/15.0.1147.100
Mozilla/5.0 (Windows NT 6.1; WOW64; Trident/7.0; AS; rv:11.0) like Gecko

Code :

shuf file | while read url; do
    wget --user-agent="$(shuf -n1 uas)" "$url"
done

If you prefer to keep your way (one url) :

data_link=(
    "https://example.com/target1.html"
    "https://example.com/target2.html"
    "https://example.com/target3.html"
    "https://example.com/target4.html"
)
user_agent=(
    "Mozilla/5.0 (iPhone; CPU iPhone OS 10_0_1 like Mac OS X) AppleWebKit/602.1.50 (KHTML, like Gecko) Version/10.0 Mobile/14A403 Safari/602.1"
    "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_3) AppleWebKit/604.5.6 (KHTML, like Gecko) Version/11.0.3 Safari/604.5.6"
    "Mozilla/5.0 (Windows 7; ) Gecko/geckotrail Firefox/firefoxversion"
)

wget --user-agent="${user_agent[RANDOM % ${#user_agent[@]} ]}" "${data_link[RANDOM % ${#data_link[@]}]}"

Your way for all urls and user-agent (both randomized) :

for i in $(seq 0 $((${#data_link[@]} -1)) | shuf); do
    wget -U "${user_agent[RANDOM % ${#user_agent[@]}]}" "${data_link[i]}"
done
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