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](https://www.google.com) -c-  
nmap [www.google.com](http://www.google.com) -sT -p 80 -oG 

Default value for variables

VAR=${VAR:-default}

Arrays and maps

declare -A res  
urls=("[www.com.ar](http://www.com.ar)" "[www.facebook.com](http://www.facebook.com)" "[www.twitter.com](http://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)