Prerequisite: Linux Command Line(I): Beginner

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File I/O

$ cat > a.txt　　#create a file 'a.txt' and appends things into it

Type random stuff...

# press Ctrl+d to exit editting

$ cat a.txt

Type random stuff...

$ cat > a.txt　　#'single >' for overwriting the entire document 

Overwritting in process...

#Ctrl+d

$ cat a.txt

Overwritting in process...

$ cat >> a.txt　　#'double >>' for  appending to the EOF

appending in process...

#Ctrl+d

$ cat a.txt

Overwritting in process...

appending in process...

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Concatenating 2 txt files

cat a.txt b.txt > out.txt　　#transfer the content of these 2 .txt and to a new .txt

cat a.txt b.txt > b.txt　　　　#error! using 'cat <' input and output cannot be same

cat a.txt >> b.txt　　　　#okay: content of a.txt appends to b.txt

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 Mkdir

Greedy method: >2 directories at a time

mkdir -p notebook/new

mkdir -p /notebook/new　　#error!

mkdir -p friends/{John, Tom, Amy}　　#with space, only 1 directory created

mkdir -p friends/{John,Tom,Amy}　　#3 directories created

rm -r friends 　　#remove non-empty directories & itself

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cd

cd ..　　# go up one directory

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output script into txt 

script out.txt

# type some commands

exit

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remove all files within a directory without removing the folder

rm Documents/*　　#suppose we are at /root

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