Special meanings of certain escaped characters

used with echo and sed

\n

means newline

\r

means return

\t

means tab

\v

means vertical tab

\b

means backspace

\a

means alert (beep or flash)

\0xx

translates to the octal ASCII equivalent of 0nn, where nn is a string of digits

Important

The $' ... ' quoted string-expansion construct is a mechanism that uses escaped octal or hex values to assign ASCII characters to variables, e.g., quote=$'\042'.

Example 5.2. Escaped Characters

#!/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

A more elaborate example:

Example 5.3. Detecting key-presses

#!/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 $?

See also Example 37.1, “String expansion”.

\"

gives the quote its literal meaning

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

\$

gives the dollar sign its literal meaning (variable name following \$ will not be referenced)

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

\\

gives the backslash its literal meaning

echo "\\"  # Results in \

# Whereas . . .

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

# However . . .

echo '\'   # Results in \