1 purpose
Read a block of text from standard input (stdin), stop reading at "EOF", and output the text to standard output (stdout).
2 Grammar
cat << EOF
文本信息
EOF
Key syntax instructions:
- << : Here Document format syntax start identifier in Linux;
- EOF : An identifier that identifies the beginning and end of text information, which can be any custom character, such as begin, data, etc.
- Text message : what the user (you) wants to display on the terminal.
3 Difference between '<< EOF' and '<<- EOF'
If the redirection operator is <<-, then all leading tab characters are stripped from input lines and the line containing delimiter.
The Chinese meaning is that if the redirection operator is <<-, then the leading tab (tab) in each line of text information and the end identifier (such as EOF above) is ignored .
#!/bin/sh
#line 1、2、3，EOF，data 1、2、3 前面为 tab，不是空格。
cat <<- EOF
line 1
line 2
line 3
EOF
cat << DATA
data 1
data 2
data 3
DATA
Results of the:
You see, the output using '<<-' ignores the tabs in front of each line .
4. Extend
What should I do if I want to input multiple lines of text into a file from the terminal?
cat > file << EOF
information 1
information 1
information 1
...
EOF