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:
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| 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
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| 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
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| 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
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| 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:
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| 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 $retained |
例2:
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| read -d '' help <<- "_EOF_"
usage: up [--level <n>| -n <levels>][--help][--version]
Report bugs to:
up home page:
_EOF_ |
例3:
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| VARIABLE1="<?xml version="1.0" encoding='UTF-8'?>
<report>
<img src="a-vs-b.jpg"/>
<caption>Thus is a future post on Multi Line Strings in bash
<date>1511</date>-<date>1512</date>.</caption>
</report>" |
例4:
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| VARIABLE2=$(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:
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| 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):
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| 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:
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| 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:
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| # create
sudo tee /aaa.txt << EOF
echo "Hello World 20314"
EOF |
例9(可向文本文件追加):
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| # Append to Sudo
sudo tee -a /aaa.txt << EOF
echo "This Line is appended"
EOF |
例如10:
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| 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:
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| 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