Một vài điều thú vị với Bash Script

var="test"
demo_variable(){
  var2="test variable"
  echo $var
  echo $var2
}

demo_variable
echo $var
echo $var2

test
test variable
test
test variable

try_local_variable(){
  local var="Test local variable"
  echo $var
}

try_local_variable
if [ -n "$var" ]
then
  echo $var
else
  echo "Parameter not supplied"
fi

Test local variable
Parameter not supplied

var="test"

var2="var"
echo "${!var2}"

test

var="test"

var2="var"
var3="${!var2}"
echo $var3

test

var="test"

# replace first 't' only
bar=${var/t/h}
echo $bar

# replace all 't'
bar=${var//t/h}
echo $bar

hest
hesh

var="this is a test"
echo "$var" | cut -d' ' -f 4
echo "$var" | cut --delimiter=' ' --fields=4

test

array1=(1 2 3)
for element in "${array1[@]}"
do
  echo $element
done

1
2
3

array1=(1 2 3)
array2=(4 5 6)
new_array=("${array1[@]}" "${array2[@]}")
for element in "${new_array[@]}"
do
  echo $element
done

1
2
3
4
5
6

array=(2 3 4)
array=(1 "${array[@]}")
for element in "${array[@]}"
do
  echo $element
done

1
2
3
4

new_array=(0)
new_array=( "${new_array[@]}" 1 )  # Cách 1
array=(2 3 4)
for element in "${array[@]}"
do
  new_array+=($element)             # Cách 2
done

for element in "${new_array[@]}"
do
  echo $element
done

0
1
2
3
4

array=(0 1 3 5)
array=( "${array[@]:0:2}" 4 "${array[@]:2}" )
for element in "${array[@]}"
do
  echo $element
done

0
1
4
3
5

array=(0 1 3 5)
array=( "${array[@]:0:2}" "${array[@]:3}" )
for element in "${array[@]}"
do
  echo $element
done

0
1
5

array=(0 1 3 5)
unset -v 'array[1]'
for element in "${array[@]}"
do
  echo $element
done

0
3
5

array=( "${array[@]/PATTERN/}" )

array=(0 1 3 5 1 2)
array=( "${array[@]/1/}" )
for element in "${array[@]}"
do
  echo $element
done

1

3
5

2

Line number 1
Line number 2

while IFS="" read -r line || [ -n "$line" ]
do
    echo $line
done < text.txt

Line number 1
Line number 2

filename="text.txt
(echo "New line added" | cat - $filename)  > "$filename".tmp && mv "$filename".tmp "$filename"
cat $filename

New line added
Line number 1
Line number 2

filename="text.txt
sed -i "1iLine number 0" $filename
cat $filename

Line number 0
Line number 1
Line number 2

filename="text.txt
echo "Line number 3" >> $filename
cat $filename

Line number 1
Line number 2
Line number 3

filename="text.txt
echo "Line number 3" > $filename
cat $filename

Line number 3

sed -i "s/PATTERN/REPLACE_PATTERN/" filename

filename="text.txt
sed -i "s/Line/This is line/" $filename
cat $filename

This is line number 1
This is line number 2

#!/usr/bin/env bash
# shellcheck disable=SC1003

# Based on https://gist.github.com/pkuczynski/8665367

parse_yaml() {
    local yaml_file=$1
    local prefix=$2
    local s
    local w
    local fs

    s='[[:space:]]*'
    w='[a-zA-Z0-9_.-]*'
    fs="$(echo @|tr @ '\034')"

    (
        sed -e '/- [^\“]'"[^\']"'.*: /s|\([ ]*\)- \([[:space:]]*\)|\1-\'$'\n''  \1\2|g' |

        sed -ne '/^--/s|--||g; s|\"|\\\"|g; s/[[:space:]]*$//g;' \
            -e "/#.*[\"\']/!s| #.*||g; /^#/s|#.*||g;" \
            -e "s|^\($s\)\($w\)$s:$s\"\(.*\)\"$s\$|\1$fs\2$fs\3|p" \
            -e "s|^\($s\)\($w\)${s}[:-]$s\(.*\)$s\$|\1$fs\2$fs\3|p" |

        awk -F"$fs" '{
            indent = length($1)/2;
            if (length($2) == 0) { conj[indent]="+";} else {conj[indent]="";}
            vname[indent] = $2;
            for (i in vname) {if (i > indent) {delete vname[i]}}
                if (length($3) > 0) {
                    vn=""; for (i=0; i<indent; i++) {vn=(vn)(vname[i])("_")}
                    printf("%s%s%s%s=(\"%s\")\n", "'"$prefix"'",vn, $2, conj[indent-1],$3);
                }
            }' |

        sed -e 's/_=/+=/g' |

        awk 'BEGIN {
                FS="=";
                OFS="="
            }
            /(-|\.).*=/ {
                gsub("-|\\.", "_", $1)
            }
            { print }'
    ) < "$yaml_file"
}

create_variables() {
    local yaml_file="$1"
    local prefix="$2"
    eval "$(parse_yaml "$yaml_file" "$prefix")"
}

default: 
  adapter: mysql2
  reconnect: true
  encoding: utf8mb4
  pool: 5
  host: local
  username: root
  password: 123456
  port: 
    - 3306
    - 33306

create_variables database.yml "config_"
echo $config_default_adapter      # Được tạo thành từ giá trị prefix, key :default và key key :adapter

for element in "${config_default_port[@]}"
do
  echo $element
done

mysql2
3306
33306