I need to write a quick bash script that asks the user which mac address should be used as a variable in the rest of the script. I can get the mac addresses using the following
ip addr | grep ether | cut -d ' ' -f6
After this, I'm not sure how to make an array of the given data, since this will depend on each machine, and then ask the user which one to choose based on an integer as input.
You can use select
select mac in `ip addr | grep ether | cut -d ' ' -f6`
do
if [[ -n $mac ]]
then
# put your command here
echo $mac
break
fi
done
Related
I had to create a bash array on Mac OS as follows. The $1 represents # of git commits you want to store in the array.
IFS=$'\n' read -rd '' -a array<<< "$(git log -n $1 | grep commit | awk '{print $2}')"
I can't access last array item as ${array[-1]}. I get the error "array: bad array subscript".
However, when I create the array on linux OS, I can access the last array item in the same way successfully.
readarray -t array <<< "$(git log -n $1 | grep commit | awk '{print $2}')"
echo ${array[-1]} is successful on Linux machine but not on Mac OS machine.
In a bash too old to support negative subscripts, you end up needing to do something like:
echo "${array[$((${#array[#]} - 1))]}"
I need to make a new array or just delete from the actual array the duplicate elements,
#The NTP IPS are the following ones:
#10.30.10.0, 10.30.10.0, 10.30.20.0, 10.30.20.0, 10.30.20.0
#!/bin/bash
ips_networks=()
for ip in ${ips_for_ntp[#]};do
ips_networks+=${ip%.*}.0
done
So I'll get ips_networks with duplicate ips, but I need just one of each ip into another array or the same, I have try with awk, set -A (Is not working on my linux), cut but with no luck, is there anyway to make an unique value array?
ips="10.30.10.0, 10.30.10.0, 10.30.20.0, 10.30.20.0, 10.30.20.0"
unique_ips=`echo $ips | sed -e "s/\s\\+//g" | sed -e "s/,/\\n/g"| sort | uniq`
echo $unique_ips #10.30.10.0 10.30.20.0
I am trying to write a script to grab the users from the passwd file
USERS_LIST=( $( cat /etc/passwd | cut -d":" -f1 ) )
the above would do the trick up until now because I only had users with no spaces in their names.
However, this is not the case anymore. I need to be able to resolve usernames that may very well have spaces in their names.
I tried reading line by line the file, but the same problem exists (this is one line but I have indented it for clarity here):
tk=($( while read line ; do
j=$(echo ${line} | cut -d":" -f1 )
echo "$j"
done < /etc/passwd )
)
unfortunately if I try to print the array, the usernames with space will be split in 2 array cells.
So username "named user" , will occupy array [0] and [1] locations.
How can I fix that in sh shell?
thank you for your help!
Arrays are bash (and ksh, and zsh) features not present in POSIX sh, so I'm assuming that you mean to ask about bash. You can't store anything in an array in sh, since sh doesn't have arrays.
Don't populate an array that way.
users_list=( $( cat /etc/passwd | cut -d":" -f1 ) )
...string-splits and glob-expands contents. Instead:
# This requires bash 4.0 or later
mapfile -t users_list < <(cut -d: -f1 </etc/passwd)
...or...
IFS=$'\n' read -r -d '' -a users_list < <(cut -d: -f1 </etc/passwd)
Now, if you really want POSIX sh compatibility, there is one array -- exactly one, the argument list. You can overwrite it if you see fit.
set --
cut -d: -f1 </etc/passwd >tempfile
while read -r username; do
set -- "$#" "$username"
done <tempfile
At that point, "$#" is an array of usernames.
I have tried everything I can think of to cut this into separate elements for my array but I am struggling..
Here is what I am trying to do..
(This command just rips out the IP addresses on the first element returned )
$ IFS=$"\n"
$ aaa=( $(netstat -nr | grep -v '^0.0.0.0' | grep -v 'eth' | grep "UGH" | sed 's/ .*//') )
$ echo "${#aaa[#]}"
1
$ echo "${aaa[0]}"
4.4.4.4
5.5.5.5
This shows more than one value when I am looking for the array to separate 4.4.4.4 into ${aaa[0]} and 5.5.5.5 into ${aaa[1]}
I have tried:
IFS="\n"
IFS=$"\n"
IFS=" "
Very confused as I have been working with arrays a lot recently and have never ran into this particular issue.
Can someone tell me what I am doing wrong?
There is a very good example on how to use IFS + read -a to split a string into an array on this other stackoverflow page
How does splitting string to array by 'read' with IFS word separator in bash generated extra space element?
netstat is deprecated, replaced by ss, so I'm not sure how to reproduce your exact problem
For a larger project that's not relevant, I need to collect system stats from the local system or a remote system. Since I'm collecting the same stats either way, I'm preventing code duplication by storing the stats-collecting commands in a Bash associative array.
declare -A stats_cmds
# Actually contains many more key:value pairs, similar style
stats_cmds=([total_ram]="$(free -m | awk '/^Mem:/{print $2}')")
I can collect local system stats like this:
get_local_system_stats()
{
# Collect stats about local system
complex_data_structure_that_doesnt_matter=${stats_cmds[total_ram]}
# Many more similar calls here
}
A precondition of my script is that ~/.ssh/config is setup such that ssh $SSH_HOSTNAME works without any user input. I would like something like this:
get_remote_system_stats()
{
# Collect stats about remote system
complex_data_structure_that_doesnt_matter=`ssh $SSH_HOSTNAME ${stats_cmds[total_ram]}`
}
I've tried every combination of single quotes, double quotes, backticks and such that I can imagine. Some combinations result in the stats command getting executed too early (bash: 7986: command not found), others cause syntax errors, others return null (single quotes around the stats command) but none store the proper result in my data structure.
How can I evaluate a command, stored in an associative array, on a remote system via SSH and store the result in a data structure in my local script?
Make sure that the commands you store in your array don't get expanded when you assign your array!
Also note that the complex-looking quoting style is necessary when nesting single quotes. See this SO post for an explanation.
stats_cmds=([total_ram]='free -m | awk '"'"'/^Mem:/{print $2}'"'"'')
And then just launch your ssh as:
sh "$ssh_hostname" "${stats_cmds[total_ram]}"
(yeah, I lowercased your variable name because uppercase variable names in Bash are really sick). Then:
get_local_system_stats() {
# Collect stats about local system
complex_data_structure_that_doesnt_matter=$( ${stats_cmds[total_ram]} )
# Many more similar calls here
}
and
get_remote_system_stats() {
# Collect stats about remote system
complex_data_structure_that_doesnt_matter=$(ssh "$ssh_hostname" "${stats_cmds[total_ram]}")
}
First, I'm going to suggest an approach that makes minimal changes to your existing implementation. Then, I'm going to demonstrate something closer to best practices.
Smallest Modification
Given your existing code:
declare -A remote_stats_cmds
remote_stats_cmds=([total_ram]='free -m | awk '"'"'/^Mem:/{print $2}'"'"''
[used_ram]='free -m | awk '"'"'/^Mem:/{print $3}'"'"''
[free_ram]='free -m | awk '"'"'/^Mem:/{print $4}'"'"''
[cpus]='nproc'
[one_min_load]='uptime | awk -F'"'"'[a-z]:'"'"' '"'"'{print $2}'"'"' | awk -F "," '"'"'{print $1}'"'"' | tr -d " "'
[five_min_load]='uptime | awk -F'"'"'[a-z]:'"'"' '"'"'{print $2}'"'"' | awk -F "," '"'"'{print $2}'"'"' | tr -d " "'
[fifteen_min_load]='uptime | awk -F'"'"'[a-z]:'"'"' '"'"'{print $2}'"'"' | awk -F "," '"'"'{print $3}'"'"' | tr -d " "'
[iowait]='cat /proc/stat | awk '"'"'NR==1 {print $6}'"'"''
[steal_time]='cat /proc/stat | awk '"'"'NR==1 {print $9}'"'"'')
...one can evaluate these locally as follows:
result=$(eval "${remote_stat_cmds[iowait]}")
echo "$result" # demonstrate value retrieved
...or remotely as follows:
result=$(ssh "$hostname" bash <<<"${remote_stat_cmds[iowait]}")
echo "$result" # demonstrate value retrieved
No separate form is required.
The Right Thing
Now, let's talk about an entirely different way to do this:
# no awful nested quoting by hand!
collect_total_ram() { free -m | awk '/^Mem:/ {print $2}'; }
collect_used_ram() { free -m | awk '/^Mem:/ {print $3}'; }
collect_cpus() { nproc; }
...and then, to evaluate locally:
result=$(collect_cpus)
...or, to evaluate remotely:
result=$(ssh "$hostname" bash <<<"$(declare -f collect_cpus); collect_cpus")
...or, to iterate through defined functions with the collect_ prefix and do both of these things:
declare -A local_results
declare -A remote_results
while IFS= read -r funcname; do
local_results["${funcname#collect_}"]=$("$funcname")
remote_results["${funcname#collect_}"]=$(ssh "$hostname" bash <<<"$(declare -f "$funcname"); $funcname")
done < <(compgen -A function collect_)
...or, to collect all the items into a single remote array in one pass, avoiding extra SSH round-trips and not eval'ing or otherwise taking security risks with results received from the remote system:
remote_cmd=""
while IFS= read -r funcname; do
remote_cmd+="$(declare -f "$funcname"); printf '%s\0' \"$funcname\" \"\$(\"$funcname\")\";"
done < <(compgen -A function collect_)
declare -A remote_results=( )
while IFS= read -r -d '' funcname && IFS= read -r -d '' result; do
remote_results["${funcname#collect_}"]=$result
done < <(ssh "$hostname" bash <<<"$remote_cmd")