BASH script

mjscott00 · 05-31-2021, 04:56 PM

I'm trying to write a script which captures all the available WiFi SSIDs in my area, then puts them into an array 'a'. I don't get an error, however, when I print the size of my array at the end of the script I get 0. I'm sure I've got my array syntax wrong, but cannot figure out what to change. Sample output is right after the code segment.
Thanks!

Code:

#!/bin/bash

a=()
n=0
sudo iwlist wlan0 scan |grep ESSID |grep -v '""' |sed 's/ESSID://' |sort |uniq |while read line; do
   echo "$n $line"
   a[$n]="$line"
   n=$((n+1))
   done
echo

echo ${#a[@]}

0 "NETGEAR03"
1 "Scott_Guest"
2 "Spyglass 2"
3 "TELUS0527"
4 "TELUS5D4C"
5 "wino911"

0

rtmistler · 05-31-2021, 05:46 PM

Looks very close.

Only suggestion is to enclose ${#a[@]} in double quotes.

I'd also echo a[n] each time you populate it to verify it's doing what you expect.

And enable bash debugging by adding:

Code:

set -vx

after the shebang line in your script. Regarding

michaelk · 05-31-2021, 06:01 PM

Code:

#!/bin/bash

a=() 
n=0
sudo iwlist wlan0 scan |grep ESSID |grep -v '""' |sed 's/ESSID://' |sort |uniq |while read line; do
   echo "$n $line"
   a[$n]="$line"  
   n=$((n+1))
   done
echo

echo ${#a[@]}

When you pipe results to a loop, it runs in a subshell so when it exits so does your array.
Untested..

Code:

a=()
while read line
do
  # perform computations on $line
  a+=($line)
done < <( sudo iwlist wlan0 scan |grep ESSID |grep -v '""' |sed 's/ESSID://' |sort |uniq  )

You can check syntax errors at https://www.shellcheck.net/

mjscott00 · 05-31-2021, 10:57 PM

Thank you Michaelk - this was exactly the issue!!!

michaelk · 06-01-2021, 07:26 AM

pan64 · 06-01-2021, 11:53 AM

Code:

sudo iwlist wlan0 scan | awk -F\" '/ESSID:/ { print $2 } '
# and if you wish to sort just add: 
awk ...    | sort -u 
# uniq is not required

But we do not need awk too:

Code:

#!/bin/bash
i=0
while read -r line
do
     L=( ${line//\"/ } )
     [[ ${L[0]} == ESSID: ]] || continue
     a[$i]="${L[1]}"
     (( i++ ))
done < <(sudo iwlist wlan scan)
printf "%s\n" "${a[@]}"

allend · 06-02-2021, 02:43 AM

If you can live without the sort

Code:

#!/bin/bash

while read line; do
  [[ "$line" =~ ESSID:\"(.+)\" ]] && echo ${BASH_REMATCH[1]}
done < <(sudo iwlist wlan0 scan)

MadeInGermany · 06-02-2021, 06:41 AM

If you have a one-character delimiter then consider IFS

Code:

i=0
while IFS=\" read -r key val junk
do
    case $key in
    ( ESSID: )
     a[i++]=$val
    esac
done < <(sudo iwlist wlan scan)
printf "%s\n" "${a[@]}"

computersavvy · 06-02-2021, 03:21 PM

It may be you are doing it wrong.
On my system I get
[/code]
$ sudo iwlist wlp4s0 scan
wlp4s0 Interface doesn't support scanning.
[/code]

Try just the basic command first to see if you get expected results then add to it until you see the expected output before you put it into the loop