Bash(and others) things that i use every day

More and more we embrace bash to do things that maybe in the past we used lower level languages (Dockerfiles , Makefiles , Pipelines etc etc), or at least that’s the way im seeing it , so im leaving some bash little things i user every day:

for loops:

for i in $(seq 0 3) ; do echo ${i} ;done
for i in {0..3} ;  do echo $i ; done
for i in "a\nb\nc" ;  do echo $i ; done

if else oneliners:

[[ $( pgrep nginx | wc -c ) > 0 ]] && echo "nginx running" || echo "nginx running"
[[ $( pgrep nginx | wc -c ) > 0 ]] && echo "nginx running" || { echo "nginx not running" , systemctl start nginx.service ; }
[[ $( pgrep nginx | wc -c ) > 0 ]] && : || { echo "nginx not running" , systemctl start nginx.service ; }

while forever:

while : ; do ss -ton | grep 80 | grep -v ESTAB ; sleep 1; done
while true ; do ss -ton | grep 80 | grep -v ESTAB ; sleep 1; done

bash expansions:

echo ${RANDOM:0:4}
echo $TERM | echo ${TERM/256color/}

merging columns:

cat list | paste - -
cat list | xargs -n 2

dynamic fd:

file <(ss)
vim <(ss)
cat <(ss)

loop line by line instead of word by word

while read l ; do echo ${l} ; done  < <( cat list| xargs -n2 )

“-” as fd to stdout

curl -s --output /dev/null https://www.google.com -c-
nmap www.google.com -sT -p 80 -oG 

Default value for variables

VAR=${VAR:-default}

Arrays and maps

declare -A res
urls=("www.com.ar" "www.facebook.com" "www.twitter.com")
for i in ${urls[@]}
do
    res[$i]=$(curl -s --output /dev/null $i  -c-  | base64)
done
for i in ${!res[@]}
do
    echo $i
    echo ${res[${i}]} | base64 --decode
done

declare -A res (declares a hash/map/dict)
urls=() (declares a list/array)
urls+=(1) (appends to list)
res["test"]="test" (creates a new entry in the map)
${res[@]} (return all values)
${!res[@]} (returns all keys)