当我们在 shell 的 bash 里操作多行内容的字符串,我们往往会想到 普通的字符串处理办法 例如:
1 2 | string="Hello linux" echo $string |
其实 bash 提供了一个非常好的解决办法,就是 “Multi-line”
变量的基本使用
e.g. 包含变量
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 | cat > myfile.txt <<EOF this file has $variable $names $inside EOF # 注入文档到 myfile.txt cat myfile.txt #输入: #this file has variable="ONE" names="TWO" inside="expanded variables" cat > myfile.txt <<EOF this file has $variable $names $inside EOF #print out the content of myfile.txt cat myfile.txt #输入: #this file has ONE TWO expanded variables |
无变量
1 2 3 4 5 6 7 8 9 | cat > myfile.txt <<"EOF" this file has $variable $dollar $name $inside EOF cat myfile.txt #得到 #this file has $variable $dollar $name $inside #PS:引用符号 "EOF" 决定是否需要输入变量 |
无变量 – 例子 2
1 2 3 4 5 6 7 8 9 | cat > myfile.txt <<EOF this file has $variable \$dollar \$name \$inside EOF cat myfile.txt # 得到 # this file has $variable $dollar $name $inside #转义 dollar "$" 符号,bash将取消变量的解析 |
将一个多行文本赋值到变量里面
例1:
1 2 3 4 5 6 7 8 | read -d '' stringvar <<-"_EOF_" all the leading dollars in the $variable $name are $retained _EOF_ # 输入变量 echo $stringvar; # all the leading dollars in the $variable $name are $retained |
例2:
1 2 3 4 5 6 | read -d '' help <<- "_EOF_" usage: up [--level <n>| -n <levels>][--help][--version] Report bugs to: up home page: _EOF_ |
例3:
1 2 3 4 5 6 | VARIABLE1="<?xml version="1.0" encoding='UTF-8'?> <report> <img src="a-vs-b.jpg"/> <caption>Thus is a future post on Multi Line Strings in bash <date>1511</date>-<date>1512</date>.</caption> </report>" |
例4:
1 2 3 4 5 6 7 8 9 | VARIABLE2=$(cat <<EOF <?xml version="1.0" encoding='UTF-8'?> <report> <img src="a-vs-b.jpg"/> <caption>Thus is a future post on Multi Line Strings in bash <date>1511</date>-<date>1512</date>.</caption> </report> EOF ) |
例5:
1 2 3 4 5 6 7 8 | VARABLE3=`cat <<EOF <?xml version="1.0" encoding='UTF-8'?> <report> <img src="a-vs-b.jpg"/> <caption>Thus is a future post on Multi Line Strings in bash <date>1511</date>-<date>1512</date>.</caption> </report> EOF` |
例6 (直接写入文件):
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 | cat > heredocfile.txt <<_EOF_ I am line 1 I am line 2 I'm the last line _EOF_ # 测试 cat heredocfile.txt # I am line 1 # I am line 2 # I'm the last line # and then, change your echo statement to include the '-e' option # which will turn on escape sequence processing: echo -e $USAGE >&2 |
例7:
1 2 3 4 5 6 7 | sudo cat > /aaaa.txt <<_EOF_ I am line 1 I am line 2 I'm the last line _EOF_ # sudo and >>: permission denied |
例8:
1 2 3 4 | # create sudo tee /aaa.txt << EOF echo "Hello World 20314" EOF |
例9(可向文本文件追加):
1 2 3 4 | # Append to Sudo sudo tee -a /aaa.txt << EOF echo "This Line is appended" EOF |
例如10:
1 2 3 4 5 6 | sudo sh -c "cat > /aaa.txt" <<"EOT" this text gets saved as sudo - $10 - ten dollars ... EOT cat /aaa.txt #this text gets saved as sudo - $10 - ten dollars ... |
例11:
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 | cat << "EOF" | sudo tee /aaa.txt let's count $one two $three four EOF cat /aaa.txt #let's count #$one #two #$three #four |
关于 tee
> tee –help
Usage: tee [OPTION]… [FILE]…
Copy standard input to each FILE, and also to standard output.
-a, –append append to the given FILEs, do not overwrite
-i, –ignore-interrupts ignore interrupt signals
–help display this help and exit
–version output version information and exit
If a FILE is -, copy again to standard output.
Report tee bugs to bug-coreutils@gnu.org
GNU coreutils home page:
General help using GNU software:
For complete documentation, run: info coreutils ‘tee invocation’
参考:
1. Heredoc Quoting – Credit to Ignacio Vazquez-Abrams: http://serverfault.com/questions/399428/how-do-you-escape-characters-in-heredoc
2. eredoc Quoting – Credit to Dennis Williamson: http://stackoverflow.com/questions/3731513/how-do-you-type-a-tab-in-a-bash-here-document
3. http://serverfault.com/questions/72476/clean-way-to-write-complex-multi-line-string-to-a-variable
4. http://arstechnica.com/civis/viewtopic.php?p=21091503
5. http://superuser.com/questions/201829/sudo-permission-denied
6. http://stackoverflow.com/questions/4937792/using-variables-inside-a-bash-heredoc
7. http://stackoverflow.com/questions/2600783/how-does-the-vim-write-with-sudo-trick-work
8. http://www.unix.com/shell-programming-scripting/187477-variables-heredoc.html
来源：http://www.woola.net/detail/2016-09-05-bash-multi-line-text.html