シェルプログラミング。変数の高度な使い方

var1="hello world hello world"
# The longest and shortest are actually the greedy and non-greedy patterns in regular expressions

# delete the data with the matching rule *lo (shortest at the beginning delete)
echo ${var1#*lo}
echo ${var1#*lo} -> world hello world

# Delete data with a match rule of *lo (longest deletion at the beginning)
echo ${var1##*lo}
-> world

# Delete data with a match rule of hel* (shortest delete at the end)
echo ${var1%hel*}
-> hello world 

# Delete data with a match rule of hel* (trailing longest delete)
echo ${var1%%hel*}
->

# Replace the first old string world with Beijing
echo ${var1/world/Beijing}
-> hello Beijing hello world

# Replace the first old string world with Beijing
echo ${var1/world/Beijing}
->hello Beijing hello Beijing

# x=${y-new-value}
echo ${y=$var1}
->hello world hello world

y=
echo ${y-$var1}
->

y=hello Beijing
echo ${y-$var1}
-> hello Beijing

# x=${y:-new value}
echo ${y:-$var1}
->hello world hello world

y=
echo ${y:-$var1}
->hello world hello world

y=hello Beijing
echo ${y:-$var1}
->hello Beijing

# x=${y+new value}
echo ${y+$var1}
->

y=
echo ${y+$var1}
-> hello world hello world

y=hello Beijing
echo ${y+var1}
->hello world hello world

# x=${y:+new value}
echo ${y:+$var1}
->

y=
echo ${y:+$var1}
->

y=hello Beijing
echo ${y:+var1}
-> hello world hello world

# x=${y=new value}
x=${y=$var1}
echo $x
->hello world hello world
echo $y
->hello world hello world

y=
x=${y=$var1}
echo $x
->
echo $y
->

y=hello Beijing
x=${y=$var1}
echo $x
-> hello world hello world
echo $y
->hello Beijing

# x=${y:=new value}
x=${y:=$var1}
echo $x
->hello world hello world
echo $y
->hello world hello world

y=
x=${y:=$var1}
echo $x
->hello world hello world
echo $y
->hello world hello world

y=hello Beijing
x=${y:=$var1}
echo $x
->hello Beijing
echo $y
->hello Beijing

# x=${y?new value}
echo ${y?$var1}
->-bash: y: hello world hello world

y=
echo ${y?$var1}
->

y=hello Beijing
echo ${y?$var1}
-> hello Beijing

# x=${y:? new value}
echo ${y?$var1}
->-bash: y: hello world hello world

y=
echo ${y:? $var1}
->-bash: y: hello world hello world

y=hello Beijing
echo ${y:? $var1}
->hello Beijing

# Method 1
var1="hello world"
echo ${#var1}
->11

# Method two
len=`expr length "$var1"`
echo $len
->11

## var1 has spaces, must add double quotes, otherwise error is reported
expr: syntax error

## var2 has no spaces, you don't need to add double quotes
var2=hello
expr length $var2
5

expr index "$var1" llo
->3

expr index "$var1" lole
->2

expr match "$var1" hel
->3

expr match "$var1" llo
->0

# Method 1
echo ${var1:2}
->llo world

# Method two
echo ${var1:2:5}
->llo w

# Method three
echo ${var1: -2}
->ldo

echo ${var1: -2:1}
->l

# Method four
echo ${var1:(3)}
->lo world

echo ${var1:(3):2}
->lo

echo ${var1:(-2):1}
->l

# Method 5
expr substr "$var1" 2 5
->ello

var2=hello
echo ${var2:2:5}
->llo

expr substr $var2 2 5
->llo

#! /bin
string="Bigdata process framework is Hadoop,Hadoop is an open source project."


function print_tips
{
 echo "=============================="
 echo "1->Print string length"
 echo "2->Delete all Hadoop" in string;
 echo "3->Replace the first Hadoop with Mapreduce"
 echo "4->Replace all Hadoops as Mapreduce"
 echo "q|Q->Quit"
 echo "=============================="
}

function len_of_string
{
 echo "${#string}"
}

function del_hadoop
{
 echo "${string//Hadoop/}"
}

function rep_first_hadoop_mapreduce
{
 echo "${string/Hadoop/Mapreduce}"
}

function rep_all_hadoop_mapreduce
{
 echo "${string//Hadoop/Mapreduce}"
}
while true
do
 echo ""
        echo ""
        echo ""
        echo ""
 echo "[string=$string]"
 print_tips
 read -p "Please input your choice (1|2|3|4|q|Q):" choice
 case $choice in
  1)len_of_string;;
  2)del_hadoop;;
  3)rep_first_hadoop_mapreduce;;
  4)rep_all_hadoop_mapreduce;;
  q|Q)exit;;
  *)echo "Error input,only in (1|2|3|4|q|Q)";;
 esac
done

# Get all users of the system and output
#! /bin
index=1
for user in `cat /etc/passwd | cut -d ":" -f 1`
do
 echo "This is the first $index user with the name: $user"
 index=$(($index + 1))
        # $(()) is mainly used for integer arithmetic, reference variables may or may not be preceded by $
done

# Calculate this year or next year based on system time
#! /bin
year=`date +%Y`
echo "This year is $year, next year is $(($year+1))year"

# Get how many weeks are left in the year and how many weeks have passed based on system time
#! /bin
# Calculate what day of the year it is
#! /bin
days=$(date +%j)
weeks=$((days/7))
remain_weeks=$((52-weeks))
echo "There are $remain_weeks weeks left in the year, $weeks have passed"

# Determine if the nginx process exists, and if not, pull it up automatically
#! /bin
nginx_process_num=$(ps -ef | grep nginx | grep -v grep | wc -l)
if [ $nginx_process_num -eq 0 ];then
 echo "nginx not started, pulling up in... "
 systemctl start nginx
else
 echo "nginx has started... "
fi

# Set to read-only
var1="hello wordl"
var1="hello shell"
declare -r var1
var1="hello java"
->-bash: var1: readonly variable

# Set to shaping
num1=20
num2=$num1+30
echo $num2
->20+30 # linux default setting is string
declare -i num3
num3=$num1+30
echo $num3
->50

# Define an array
declare -a array
array=(1 2 3 4)
# Output the entire contents
echo ${array[@]} 
# Output the contents with subscript index 1
echo ${array[1]}
# The number of elements in the array
echo ${#array[@]}
# Specify the index assignment
array[0]=555
# Add elements at the end
array[4]=666
# Delete an element
# Delete the element with index 2
unset array[2]
# Clear the entire array
unset array
# Access in pieces
# Show the three elements of the array with subscript indexes starting from 1 to 3 (wrap the head and not the tail)
${array[@]:1:4}
# Array traversal
for n in ${array[@]}
do
    echo $n
done

# Show all functions defined before the script and their contents
# Add declare -f after the print_tips method that you tried before, and you'll see that only the functions and content before the command are displayed

num1=20
num2=100
expr $num1 \| $num2
expr $num1 \& $num2
expr $num1 \< $num2
expr $num1 \<= $num2
expr $num1 \> $num2
expr $num1 \>= $num2
expr $num1 = $num2
expr $num1 ! = $num2
expr $num1 + $num2
expr $num1 - $num2
expr $num1 \* $num2
expr $num1 / $num2
expr $num1 % $num2

bc
bc 1.06.95
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