5.2. 转义

某些转义字符的特殊含义

与 echo 和 sed 一起使用

\n

表示换行符

\r

表示回车符

\t

表示制表符

\v

表示垂直制表符

\b

表示退格符

\a

表示 alert (蜂鸣或闪烁)

\0xx

转换为八进制 ASCII 等效于0nn，其中nn是一个数字字符串

这个$' ... ' 带引号的 字符串扩展结构是一种机制，它使用转义的八进制或十六进制值来为变量分配 ASCII 字符，例如，quote=$'\042'。

示例 5-2. 转义字符

#!/bin/bash # escaped.sh: escaped characters ############################################################# ### First, let's show some basic escaped-character usage. ### ############################################################# # Escaping a newline. # ------------------ echo "" echo "This will print as two lines." # This will print # as two lines. echo "This will print \ as one line." # This will print as one line. echo; echo echo "=============" echo "\v\v\v\v" # Prints \v\v\v\v literally. # Use the -e option with 'echo' to print escaped characters. echo "=============" echo "VERTICAL TABS" echo -e "\v\v\v\v" # Prints 4 vertical tabs. echo "==============" echo "QUOTATION MARK" echo -e "\042" # Prints " (quote, octal ASCII character 42). echo "==============" # The $'\X' construct makes the -e option unnecessary. echo; echo "NEWLINE and (maybe) BEEP" echo $'\n' # Newline. echo $'\a' # Alert (beep). # May only flash, not beep, depending on terminal. # We have seen $'\nnn" string expansion, and now . . . # =================================================================== # # Version 2 of Bash introduced the $'\nnn' string expansion construct. # =================================================================== # echo "Introducing the \$\' ... \' string-expansion construct . . . " echo ". . . featuring more quotation marks." echo $'\t \042 \t' # Quote (") framed by tabs. # Note that '\nnn' is an octal value. # It also works with hexadecimal values, in an $'\xhhh' construct. echo $'\t \x22 \t' # Quote (") framed by tabs. # Thank you, Greg Keraunen, for pointing this out. # Earlier Bash versions allowed '\x022'. echo # Assigning ASCII characters to a variable. # ---------------------------------------- quote=$'\042' # " assigned to a variable. echo "$quote Quoted string $quote and this lies outside the quotes." echo # Concatenating ASCII chars in a variable. triple_underline=$'\137\137\137' # 137 is octal ASCII code for '_'. echo "$triple_underline UNDERLINE $triple_underline" echo ABC=$'\101\102\103\010' # 101, 102, 103 are octal A, B, C. echo $ABC echo escape=$'\033' # 033 is octal for escape. echo "\"escape\" echoes as $escape" # no visible output. echo exit 0

一个更详细的示例

示例 5-3. 检测按键

#!/bin/bash # Author: Sigurd Solaas, 20 Apr 2011 # Used in ABS Guide with permission. # Requires version 4.2+ of Bash. key="no value yet" while true; do clear echo "Bash Extra Keys Demo. Keys to try:" echo echo "* Insert, Delete, Home, End, Page_Up and Page_Down" echo "* The four arrow keys" echo "* Tab, enter, escape, and space key" echo "* The letter and number keys, etc." echo echo " d = show date/time" echo " q = quit" echo "================================" echo # Convert the separate home-key to home-key_num_7: if [ "$key" = $'\x1b\x4f\x48' ]; then key=$'\x1b\x5b\x31\x7e' # Quoted string-expansion construct. fi # Convert the separate end-key to end-key_num_1. if [ "$key" = $'\x1b\x4f\x46' ]; then key=$'\x1b\x5b\x34\x7e' fi case "$key" in $'\x1b\x5b\x32\x7e') # Insert echo Insert Key ;; $'\x1b\x5b\x33\x7e') # Delete echo Delete Key ;; $'\x1b\x5b\x31\x7e') # Home_key_num_7 echo Home Key ;; $'\x1b\x5b\x34\x7e') # End_key_num_1 echo End Key ;; $'\x1b\x5b\x35\x7e') # Page_Up echo Page_Up ;; $'\x1b\x5b\x36\x7e') # Page_Down echo Page_Down ;; $'\x1b\x5b\x41') # Up_arrow echo Up arrow ;; $'\x1b\x5b\x42') # Down_arrow echo Down arrow ;; $'\x1b\x5b\x43') # Right_arrow echo Right arrow ;; $'\x1b\x5b\x44') # Left_arrow echo Left arrow ;; $'\x09') # Tab echo Tab Key ;; $'\x0a') # Enter echo Enter Key ;; $'\x1b') # Escape echo Escape Key ;; $'\x20') # Space echo Space Key ;; d) date ;; q) echo Time to quit... echo exit 0 ;; *) echo You pressed: \'"$key"\' ;; esac echo echo "================================" unset K1 K2 K3 read -s -N1 -p "Press a key: " K1="$REPLY" read -s -N2 -t 0.001 K2="$REPLY" read -s -N1 -t 0.001 K3="$REPLY" key="$K1$K2$K3" done exit $?

另请参阅 示例 37-1。

\"

赋予引号字面意义

echo "Hello" # Hello echo "\"Hello\" ... he said." # "Hello" ... he said.

\$

赋予美元符号字面意义 (跟随 \$ 的变量名将不会被引用)

echo "\$variable01" # $variable01 echo "The book cost \$7.98." # The book cost $7.98.

\\

赋予反斜杠字面意义

echo "\\" # Results in \ # Whereas . . . echo "\" # Invokes secondary prompt from the command-line. # In a script, gives an error message. # However . . . echo '\' # Results in \