#!/bin/sh -u
#     $0   (no arguments)
# A script that demonstrates a wide variety of Here Documents.
#
# -IAN! idallen@ncf.ca   July 2001

# Some systems put gzip in /usr/local/bin - add it to PATH
#
export PATH=/bin:/usr/bin:/usr/local/bin
umask 022

if [ "$#" -ne 0 ]; then
	echo 1>&2 "$0: Expecting zero arguments.  You gave me $# ($*)."
	exit 1
fi

############################################################################
# The most basic Here Document simply copies text onto your screen.
#
cat <<EOF

    HERE DOCUMENT #1

    This is a familiar Here Document, used as standard input to the cat
    command.  The word EOF is not quoted, so this text is treated as if it
    were "double-quoted" by the shell.  That means shell variables, such
    as $SHELL and $HOME,
    and command substitutions, such as $(hostname)
    are expanded before the text is handed to the "cat" command as stdin.

    It is the shell that expands the variables before handing the input to
    "cat" - "cat" does not expand variables.

    Standard output is not redirected, so it appears on your screen.
    This is easier than using a whole bunch of "echo" commands that
    would require many, many quotes around the arguments.

EOF

############################################################################
# This next piece of text needs to be sorted to be understood.
# The sort commmand does exactly that; read what it says on stdout.
#
sort <<sort

  B
  F 
  E standard input.  
  A HERE DOCUMENT #2
  C This is a silly use of a Here Document.  It demonstrates that
  K are expanded before the text is handed to the "cat" command as stdin.
  D you can have the shell send text into any program that reads from
  J $SHELL and $HOME
  I by the shell.  That means shell variables, such as
  H not quoted, so this text is treated as if it were "double-quoted"
  G Again, since the word that delimites the Here Document ("sort") is

sort

############################################################################
# This next command selects lines that are *not* comment lines.
#
grep -v '^#' <<+++

  HERE DOCUMENT #3

# These comments are ignored by the grep "-v" option.
# The grep command ignores the comment lines in this text coming on stdin.
  You can send text into any program you like.
# I wonder if he knows what he is talking about?
  The program will read the text on stdin.
# I hope these comments don't appear in the output.
  The delimiter that starts and ends the Here Document can be any
  single word.
# I think that's enough to demonstrate the concept.

+++

############################################################################
tail -7 <<'eof'

  You can say anything you like up here - the "tail" command will
  only show the last five lines of this standard input text.

  If the word that delimits the Here Document is quoted in any way,
  then the document is treated as if it were all single-quoted and the
  shell does not expand anything (even variables) in the text.

  HERE DOCUMENT #4

  This means you won't see these expanded:
     $SHELL
     $HOME
     $USER

eof

############################################################################
# You can supply standard input to any program you like...
#
tr 'a-zA-Z' 'n-za-mN-ZA-M' <<secret
  
  URER QBPHZRAG #5

  Guvf vf gur snzbhf "ebg13" rapelcgvba hfrq ba gur Vagrearg gb uvqr
  cbgragvnyyl bssrafvir zngrevny sebz pnfhny ivrjref.  V rapelcgrq
  guvf cnentencu naq cynprq vg vagb gur furyy fpevcg urer.  Gur
  genafyngr pbzznaq qbrf gur qrpelcgvba ol ebgngvat nyy gur yrggref
  onpx gb gurve bevtvany cynprf.

  Abgvpr gung inevnoyrf ner rkcnaqrq *orsber* gur vachg vf unaqrq gb gur
  pbzznaq, fb vs lbh gel gb hfr rapelcgrq inevnoyr anzrf fhpu nf FURYY
  be UBZR, gurl jba'g or erpbtavmrq ol gur furyy.  (Vs lbh hfr gur "-h"
  bcgvba gb ercbeg haqrsvarq inevnoyrf, lbh jbhyq trg na reebe vs lbh
  gevrq gb hfr gur abarkvfgrag rapelcgrq inevnoyr anzr.)

secret

############################################################################
# The fmt command will format text into nice paragraphs for you.
#
fmt <<EOF
  
  HERE
  DOCUMENT
  #6

  EOF
  is probably the most common Here Document delimiter.
  The delimiter must always
  appear at the left
  margin
  (no spaces in front)
  and
  many shells won't recognize it if it has any trailing
  spaces
  on the same line.
  So, be sure your Here Document end delimiter has no blanks
  after it.
  
EOF

############################################################################
write "$USER" <<msg

  HERE DOCUMENT #7

  You can prepare a message and send it to yourself using the write
  command (which, like most Unix commands, reads from standard input).

  Hello!

msg

############################################################################
# Provide a Here Document as standard input to gzip.
# Create a unique tmp file name for output of gzip.
# Put the name in a variable to make it easy to use in several places.
#
tmpfile="/tmp/$USER.$$.gz"
gzip >"$tmpfile" <<zip

  HERE DOCUMENT #8

  You can prepare a little piece of text and send it as stdin to any
  command that reads stdin.  Here, we send this text to be compressed
  into a file.  Since dollar variables expand if the delimiter word is
  not quoted, you can use command substitutions such as

$(who)

  or
     
$(grep "^$USER" /etc/passwd | tr ':' '\n')

  to have the shell add more text to your Here Document.

zip

file "$tmpfile"
ls -l "$tmpfile"
gzip -d <"$tmpfile"
rm "$tmpfile"    # don't keep the tmp file

############################################################################
# Here, stdin for "sort" comes from the Here Document.
# The "sort" stdout goes into the pipe.
# The "tr" stdout goes to the next pipe.
# The "cut" stdout goes to your screen.
#
sort <<secret | tr 'a-zA-Z' 'n-za-mN-ZA-M' | cut -c 2-

2 
6 
1 URER QBPHZRAG #9
5 bgure Havk pbzznaqf.
7 Gur Urer Qbphzrag vf whfg n jnl bs cnffvat n srj yvarf bs grkg gb gur
9 svyr gb ubyq vg.  Gur grkg pna or xrcg vafvqr gur furyy fpevcg vgfrys.
4 vachg pna vgfrys unir vgf fgnaqneq bhgchg erqverpgrq be cvcrq vagb
8 fgnaqneq vachg bs fbzr pbzznaq jvgubhg univat gb perngr n frcnengr
3 Bs pbhefr, gur pbzznaq gung erprvirf gur Urer Qbphzrag nf fgnaqneq

secret

############################################################################
# This programmer made a mistake:
#
sort /etc/resolv.conf <<EOF

  HERE DOCUMENT #10

  Of course, you can have the $SHELL go to all the work of preparing a
  Here Document, and then find that the command that you are using is
  either not designed to read standard input, or is currently ignoring
  standard input (perhaps because you specified a file name?).

  Be careful that you supply the Here Document to a command that is
  ready and able to read standard input!

  This Here Document is being ignored by the "sort" command.

EOF

# That's all!
#
exit 0