preface
Try not to use all the questions. The commands tail, cat, grep and awk are directly executed to get the results. They are all programmed with bash shell statements, so the program is the most efficient
The following is my method of learning Shell for reference
1. Take half a day to see the basic usage: Shell tutorial - rookie tutorial
Note: if you find it boring to watch it directly, you can spend half a day brushing the first five simple questions of Niuke, look at the writing methods of the top few, get started a little, and then watch the rookie tutorial
2. Then take the Niuke Shell title It takes one day to finish the brush, but it won't. look at what others have written in the ranking. Try to follow their own ideas and complete it by yourself. Be sure to think and knock by yourself. Don't copy other people's operation. You can read other people's ideas and write by yourself, but don't look and write. It will take about two days in total. There will be no problem in the development of basic points of shell programming. You can learn faster and more deeply by doing more
If you think and complete 20 questions by yourself, there will be no problem with shell grammar and basic programming. Anyway, I feel so. I concentrate on brushing them in time
subject
20 channels
1. Count file lines
subject
describe Write one bash Script to output a text file nowcoder.txt Number of rows in ...
code
while read val # Read line by line, val is each line do # Every line read is + 1, that is, self increment ((line++)) done < ./nowcoder.txt # Redirect to the file every time you finish, continue reading, < indicates redirection echo $line
2. Print the last 5 lines of the file
The code is directly on the back
#!/bin/bash
line=0
while read val
do
line=$((line+1))
done < nowcoder.txt
line=$((line-5))
cnt=0
while read val
do
if (($cnt >= $line )) # It is equivalent to not inputting in front of line, but inputting in the back of line
then
echo $val
fi
cnt=$((cnt+1))
done < nowcoder.txt
3. Multiple of output 7
for i in {0..500}
do
if (( i % 7 == 0))
then
echo $i
fi
done
4. Output line 5
#!bin/bash
num=1
while read line
do
if ((num == 5))
then
echo $line
fi
((num++))
done < nowcoder.txt
5. Print line number of blank line
#!/bin/bash
num=1
while read line
do
if [ -z $line ]
then
echo $num
fi
((num++))
done < nowcoder.txt
6. Remove blank lines
#!/bin/bash
while read line
do
if [ -z $line ]
then
continue
else
echo $line
fi
done < nowcoder.txt
7. Print words with letters less than 8
# Idea 1: first divide and store in the array, and then count them separately
# Idea 2: traverse the string, num=0, judge when you encounter a space, and see if it can be output
#!/bin/bash
read line < nowcoder.txt # Read nowcoder Txt line
for n in $line
do
if [ "${#n}" -lt 8 ]
then
echo ${n}
fi
done
8. Count the sum of the memory occupied by all processes
# Read each row, then get the second column value and add it
sum=0
while read line
do
arr=($line)
((sum+=arr[5]))
done < nowcoder.txt
echo $sum
9. Count the number of occurrences of each word
The number of typical questions, de duplication and statistics are the same
# Problem solving steps:
# 1. Read line by line. The words of each line are stored in the map, which is equivalent to an initialization process
# 2. Use an array to store the number of occurrences of words after duplication
# 3. Bubble sorting
# 4. Compare the number of times after sorting with the value in the map, and output them in turn when they are equal. This is the sorted number
declare -A map
while read line
do
arr=$line
for i in ${arr[@]}
do
if [ -z ${map[$i]} ]
then
map[$i]=1
else
((map[$i]++))
fi
done
done < nowcoder.txt
mm=()
for value in ${map[@]}
do
mm[${#mm[@]}]=${value}
done
len=${#mm[@]}
for ((i=0;i<len;i++))
do
for ((j=i+1;j<len;j++))
do
if [ ${mm[$i]} -gt ${mm[$j]} ]
then
tmp=${mm[$i]}
mm[$i]=${mm[$j]}
mm[$j]=$tmp
fi
done
done
for ((k=0;k<len;k++))
do
for key in ${!map[@]}
do
if [ ${map[$key]} -eq ${mm[$k]} ]
then
echo $key ${map[$key]}
fi
done
done
10. Is there any repetition in the second column
# Problem solving steps
# 1. Construct a map, and the key value is the number of occurrences of the element in column 2
# 2. Put the number of occurrences of elements in the map into the array
# 3. Sort array
# 4. Output in sort order
declare -A map
# Step 1: construct map
while read -a line
do
key=${line[1]}
if [ -z ${map[${key}]} ]
then
map[${key}]=1
else
((map[${key}]++))
# echo $key ${map[${key}]}
fi
done < nowcoder.txt
# Step 2: put the number of repeated elements into the array
arr=()
for key in ${!map[@]}
do
if [ ${map[$key]} -gt 1 ]
then
echo ${map[$key]} $key
arr[${#arr[@]}]=${map[$key]}
fi
done
# Step 3: sort the arr array (number of occurrences)
len=${#arr{@}}
for (( i=0;i<len;i++ ))
do
for (( j=$[$i+1];j<len;j++ ))
do
if [ ${arr[$i]} -gt ${arr[$j]} ]
then
# exchange
tmp=${arr[$i]}
arr[$i]=${arr[$j]}
arr[$j]=$tmp
fi
done
done
#Step 4: output
for (( k=0;k<len;k++ ))
do
for key in ${!map[@]}
do
if [ ${map[${key}]} -eq ${arr[$k]} ]
then
echo ${map[$key]} ${key}
fi
done
done
11. Transpose the contents of the file
# Read each row, get the number of trips and columns, and then traverse. Note that the shell has no two-dimensional array, but only one-dimensional array
# Step 1: read each row and put it into the array
arr=()
while read line
do
arr[${#arr[@]}]=$line
done < nowcoder.txt
# Step 2: transpose output, that is, row column exchange traversal output
rows=${#arr[@]}
m=(${arr[0]})
columns=${#m[@]}
for (( i=0;i<$columns;i++ ))
do
for (( j=0;j<$rows;j++ ))
do
tmp=(${arr[$j]})
echo "${tmp[$i]} "
done
done
12. Print the number of digits in each line
# String interception, regular expression
line_num=0 # Line number
sum=0 # Total number of figures
while read line
do
count=0 # Record the number of digits in each line
((line_num++))
for (( i=0;i<${#line};i++ ))
do
if [[ ${line:$i:1} =~ [1-5] ]]
then
((count++))
fi
done
((sum+=count))
echo "line${line_num} number:${count}"
done < nowcoder.txt
echo "sum is ${sum}"
13. Remove all sentences containing this
# Read each row and generate an array for each row to see whether it contains this. If yes, continue. Otherwise, output
while read line
do
flag=0
for i in $line
do
if [ $i == "this" ] # Note the difference between = = and - eq, = = compares strings, and - eq compares corresponding values
then
flag=1
break
fi
done
if [ $flag -eq 0 ]
then
echo $line
fi
done < nowcoder.txt
14. Average
read len # Input length
loop_time=$len
sum=0
while (($loop_time > 0))
do
read ele
((sum+=ele))
((loop_time--))
done
echo "scale=3;$sum/$len" | bc # The bc tool displays decimals
15. Remove unnecessary words
# Read input
while read line
do
len=${#line}
flag=1
# Determine each character of the string
for (( i=0;i<len;i++ ))
do
if [[ ${line:$i:1} == "B" || ${line:$i:1} == "b" ]]
then
flag=0
break
fi
done
if [ $flag -eq 1 ]
then
echo $line
fi
done
16. Judge whether the input is an IP address
# It is composed of four digits, and the range of digits is 0 ~ 255
# How does Shell do separation? Press. Separated, returned to array, ${parameter//pattern/string}
while read line
do
arr=(${line//./ })
len=${#arr[@]}
if [[ $len != 4 ]]
then
echo "error"
continue
fi
flag=1
for ele in ${arr[@]}
do
if [ $ele -ge 0 -a $ele -le 255 ]
then
continue
else
flag=0
break
fi
done
if [ $flag -eq 1 ]
then
echo "yes"
else
echo "no"
fi
done < nowcoder.txt
17. Output the fields in reverse order to each line of the file
awk here will be faster and easier to understand. I use shell statements to write it myself. It's not easy to write
# NF indicates how many words are in a line, - F ":" indicates separated by:
awk -F ":" '{ for(i=NF;i>=1;i--)
if (i != 1){
{printf $i ":"}
} else {
{print $i}
}
}' nowcoder.txt
18. Count and sort domain names
# This is similar to string repetition times and sorting
declare -A map
while read line
do
tmp=(${line//\//}) # backslash escape
name=${map[${tmp[1]}]}
# echo $name
if [ -z $name ]
then
map[${tmp[1]}]=1
else
((map[${tmp[1]}]++))
fi
done < nowcoder.txt
# Construct array
arr=()
for key in ${!map[@]}
do
arr[${#arr[@]}]=${map[$key]}
done
len=${#arr[@]}
# Bubble is used to sort the array (descending)
for (( i=0;i<len;i++ ))
do
for (( j=i+1;j<len;j++ ))
do
if [ ${arr[$i]} -lt ${arr[$j]} ]
then
tmp=${arr[$i]}
arr[$i]=${arr[$j]}
arr[$j]=$tmp
fi
done
done
# Output in array sort order
for (( k=0;k<len;k++ ))
do
for key in ${!map[@]}
do
if [ ${map[${key}]} -eq ${arr[$k]} ]
then
echo ${map[$key]} ${key}
fi
done
done
19. Print isosceles triangles
I remember learning C language at the beginning. This is the textbook exercise
for (( i=1;i<=5;i++ ))
do
# Print spaces
for (( j=5-i;j>=1;j-- ))
do
printf " "
done
# Print stars
for (( k=1;k<=i;k++ ))
do
printf "* "
done
printf "\n"
done
20. Print a line with only one number
while read line
do
count=0
for (( i=0;i<${#line};i++ ))
do
if [[ ${line:$i:1} =~ [0-9] ]]
then
((count++))
fi
done
if [ $count -eq 1 ]
then
echo $line
fi
done < nowcoder.txt