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Linux Command - cat

cat - concatenate and print files to stdout

cat file1.txt              # print contents of file

cat file1.txt file2.txt    # print contents of multiple files

cat file1.txt > file2.txt  # overwrite file2.txt with file1.txt
cat file1.txt >> file2.txt  # append instead of overwrite

cat one two > combined     # combine 2 files into 1

cat test1.txt | grep test  # pipe output, filter with grep
cat test1.txt | wc -l      # pipe output, count lines

-A show all ( same as -vET )
-b number non-empty output lines ( override -n )
-e same as vE
-E show ends ( $ at end of line )
-n number all output lines
-s squeeze blank, filter out blank, repeated lines
-t same as -vT
-T show tabs
-v show non printing characters

You can write multiple lines to a file like this. It will read in what ever you type, line at a time until you type [CTRL]-D.

cat > test1.txt
Line of text.
Another line of text.

You can use the following to read in text line at a time until it encounters EOF. It will then create/write/overwrite the file.

cat << EOF > test1.txt
Line of text.
Another line of text.