shell here document usage sample

heredoc-argoff-2.sh

#!/bin/bash
# generate-script.sh
# Based on an idea by Albert Reiner.

OUTFILE=generated.sh         # Name of the file to generate.


# -----------------------------------------------------------
# 'Here document containing the body of the generated script.
(
cat < <'EOF'
#!/bin/bash

echo "This is a generated shell script."
#  Note that since we are inside a subshell,
#+ we can't access variables in the "outside" script.

echo "Generated file will be named: $OUTFILE"
#  Above line will not work as normally expected
#+ because parameter expansion has been disabled.
#  Instead, the result is literal output.

a=7
b=3

let "c = $a * $b"
echo "c = $c"

exit 0
EOF
) > $OUTFILE
# -----------------------------------------------------------

#  Quoting the 'limit string' prevents variable expansion
#+ within the body of the above 'here document.'
#  This permits outputting literal strings in the output file.

if [ -f "$OUTFILE" ]
then
  chmod 755 $OUTFILE
  # Make the generated file executable.
else
  echo "Problem in creating file: \"$OUTFILE\""
fi

#  This method can also be used for generating
#+ C programs, Perl programs, Python programs, Makefiles,
#+ and the like.

exit 0

heredoc-argoff.sh

#!/bin/bash
#  A 'cat' here-document, but with parameter substitution disabled.

NAME="John Doe"
RESPONDENT="the author of this fine script"  

cat < <'Endofmessage'

Hello, there, $NAME.
Greetings to you, $NAME, from $RESPONDENT.

Endofmessage

#   No parameter substitution when the "limit string" is quoted or escaped.
#   Either of the following at the head of the here document would have
#+  the same effect.
#   cat <<"Endofmessage"
#   cat <<\Endofmessage

exit

heredoc-argsub.sh

#!/bin/bash
# Another 'cat' here document, using parameter substitution.

# Try it with no command-line parameters,   ./scriptname
# Try it with one command-line parameter,   ./scriptname Mortimer
# Try it with one two-word quoted command-line parameter,
#                           ./scriptname "Mortimer Jones"

CMDLINEPARAM=1     #  Expect at least command-line parameter.

if [ $# -ge $CMDLINEPARAM ]
then
  NAME=$1          #  If more than one command-line param,
                   #+ then just take the first.
else
  NAME="John Doe"  #  Default, if no command-line parameter.
fi  

RESPONDENT="the author of this fine script"  
  

cat < 

heredoc-commentblock.sh

#!/bin/bash
# commentblock.sh

: <<COMMENTBLOCK
echo "This line will not echo."
This is a comment line missing the "#" prefix.
This is another comment line missing the "#" prefix.

&*@!!++=
The above line will cause no error message,
because the Bash interpreter will ignore it.
COMMENTBLOCK

echo "Exit value of above \"COMMENTBLOCK\" is $?."   # 0
# No error shown.
echo


#  The above technique also comes in useful for commenting out
#+ a block of working code for debugging purposes.
#  This saves having to put a "#" at the beginning of each line,
#+ then having to go back and delete each "#" later.
#  Note that the use of of colon, above, is optional.

echo "Just before commented-out code block."
#  The lines of code between the double-dashed lines will not execute.
#  ===================================================================
: <<DEBUGXXX
for file in *
do
 cat "$file"
done
DEBUGXXX
#  ===================================================================
echo "Just after commented-out code block."

exit 0



######################################################################
#  Note, however, that if a bracketed variable is contained within
#+ the commented-out code block,
#+ then this could cause problems.
#  for example:


#/!/bin/bash

  : <<COMMENTBLOCK
  echo "This line will not echo."
  &*@!!++=
  ${foo_bar_bazz?}
  $(rm -rf /tmp/foobar/)
  $(touch my_build_directory/cups/Makefile)
COMMENTBLOCK


$ sh commented-bad.sh
commented-bad.sh: line 3: foo_bar_bazz: parameter null or not set

# The remedy for this is to strong-quote the 'COMMENTBLOCK' in line 49, above.

  : <<'COMMENTBLOCK'

# Thank you, Kurt Pfeifle, for pointing this out.

heredoc-func.sh

#!/bin/bash
# here-function.sh

GetPersonalData ()
{
  read firstname
  read lastname
  read address
  read city 
  read state 
  read zipcode
} # This certainly looks like an interactive function, but...


# Supply input to the above function.
GetPersonalData < 
或者可以像下面这种匿名功能一样：

#!/bin/bash

: < 

heredoc-selfdoc.sh

#!/bin/bash
# self-document.sh: self-documenting script
# Modification of "colm.sh".

DOC_REQUEST=70

if [ "$1" = "-h"  -o "$1" = "--help" ]     # Request help.
then
  echo; echo "Usage: $0 [directory-name]"; echo
  sed --silent -e '/DOCUMENTATIONXX$/,/^DOCUMENTATIONXX$/p' "$0" |
  sed -e '/DOCUMENTATIONXX$/d'; exit $DOC_REQUEST; fi


: <<DOCUMENTATIONXX
List the statistics of a specified directory in tabular format.
---------------------------------------------------------------
The command-line parameter gives the directory to be listed.
If no directory specified or directory specified cannot be read,
then list the current working directory.

DOCUMENTATIONXX

if [ -z "$1" -o ! -r "$1" ]
then
  directory=.
else
  directory="$1"
fi  

echo "Listing of "$directory":"; echo
(printf "PERMISSIONS LINKS OWNER GROUP SIZE MONTH DAY HH:MM PROG-NAME\n" \
; ls -l "$directory" | sed 1d) | column -t

exit 0

heredoc-simple.sh

#!/bin/bash

# Noninteractive use of 'vi' to edit a file.
# Emulates 'sed'.

E_BADARGS=85

if [ -z "$1" ]
then
  echo "Usage: `basename $0` filename"
  exit $E_BADARGS
fi

TARGETFILE=$1

# Insert 2 lines in file, then save.
#--------Begin here document-----------#
vi $TARGETFILE <.

#  Bram Moolenaar points out that this may not work with 'vim'
#+ because of possible problems with terminal interaction.

exit

heredoc-tab.sh

#!/bin/bash
cat < <- HERE
          include leading tab
      include leading space
HERE
exit 0

heredoc.sh

 #!/bin/bash
    
    wall < 
    --------

hi, dear author, for this script , heredoc-argsub.sh(the third one) I have tried and find the warning , is it not complete , thanks for your instructions , best wishes!

@whiteorchid

hi, dear author, for this script , heredoc-argsub.sh(the third one) I have tried and find the warning , is it not complete , thanks for your instructions , best wishes!

Based on the description in the bottom of heredoc-argoff.sh, the opposite rule would ideally say, that if you have a non-quoted "limit string" then the parameter substitution will happen.

Also note that the heredoc-marker seems wrong in the body of the examples, but is correctly written in the bottom descriptions, so i assume, every occurrence of cat < < should be cat << without a space between the two <

That rule in mind, the heredoc-argsub.sh could be like below (i tested all three execution ways right now)

#!/bin/bash
# Another 'cat' here document, using parameter substitution.

# Try it with no command-line parameters,   ./scriptname
# Try it with one command-line parameter,   ./scriptname Mortimer
# Try it with one two-word quoted command-line parameter,
#                           ./scriptname "Mortimer Jones"

CMDLINEPARAM=1     #  Expect at least command-line parameter.

if [ $# -ge $CMDLINEPARAM ]
then
  NAME=$1          #  If more than one command-line param,
                   #+ then just take the first.
else
  NAME="John Doe"  #  Default, if no command-line parameter.
fi

RESPONDENT="the author of this fine script"

cat <<Endofmessage

Hello, there, $NAME.
Greetings to you, $NAME, from $RESPONDENT.

Endofmessage

# Parameter substitution works when the "limit string" is unquoted.

exit