SEO

simple question...

cat << EOF
foo
bar
EOF

echos foo and bar...

The question is - is that the shell (bash) or ??? that supports that
function?

Simple question I'm sure, but googling for << doesn't work....


Either zsh supports that as well or it's not bash... I'm confused.

Ray

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ray wrote:
> simple question...
>
> cat << EOF
> foo
> bar
> EOF
>
> echos foo and bar...
>
> The question is - is that the shell (bash) or ??? that supports that
> function?
>
> Simple question I'm sure, but googling for << doesn't work....
>
>
> Either zsh supports that as well or it's not bash... I'm confused.

It's called a "here document". Google for that term, and you'll get a
much better explanation than I can give.

But, in brief
it is a feature of the shell; bash supports it, and (apparently) so does
zsh.

The construct
<<something
data
data
something

tells the shell to collect all the lines following the <<something, up
to but not including the trailing 'something' and feed that data into
the processes stdin.

Shell variable expansion will be performed, given the suitable set up of
your shell.

So, for instance,
DATE=`date`
cat >/etc/issue.net <<EOF
Hello there. This file was built on $DATE
You have reached my system. Nice, isnt it?
EOF

will expand the $DATE field, and copy the resulting text into your
/etc/issue.net file

See bash(1) for details
You might also read http://www.faqs.org/docs/abs/HTML/here-docs.html




- --

Lew Pitcher, IT Specialist, Enterprise Data Systems
Enterprise Technology Solutions, TD Bank Financial Group

(Opinions expressed here are my own, not my employer's)
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Lew Pitcher wrote:

> It's called a "here document". Google for that term, and you'll get a
> much better explanation than I can give.
>

> See bash(1) for details
> You might also read http://www.faqs.org/docs/abs/HTML/here-docs.html
>
awesome, thanks!

I've used it in perl, but didn't know bash supported it (until recently)
and didn't know the name of it.

I'm a windows batch file guy at work... moving to perl and bash has been
both enlighting and confusing and wonderful and overwhelming at the same
time.
(cygwin and perl are starting to show up in my scripts at work...)

Ray

On Tue, 07 Jun 2005 12:33:07 -0400, Lew Pitcher <Lew.Pitcher@td.com> wrote:
>
> So, for instance,
> DATE=`date`
> cat >/etc/issue.net <<EOF
> Hello there. This file was built on $DATE
> You have reached my system. Nice, isnt it?
> EOF
>
> will expand the $DATE field, and copy the resulting text into your
> /etc/issue.net file

Did you actualy _try_ that? Indented EOF needs a '-' elsewhere

I'll let you find elsewhere...

--Grant.

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Grant Coady wrote:
> On Tue, 07 Jun 2005 12:33:07 -0400, Lew Pitcher <Lew.Pitcher@td.com> wrote:
>
>>So, for instance,
>> DATE=`date`
>> cat >/etc/issue.net <<EOF
>> Hello there. This file was built on $DATE
>> You have reached my system. Nice, isnt it?
>> EOF
>>
>>will expand the $DATE field, and copy the resulting text into your
>>/etc/issue.net file
>
>
> Did you actualy _try_ that? Indented EOF needs a '-' elsewhere
>
> I'll let you find elsewhere...
>
> --Grant.
>

FWIW, in usenet posts and emails, I typically indent code examples by
two characters to highlight them /as code examples/. The indentation (in
the post) isn't meant to be copied literally.

As for the '-', then
DATE=`date`
cat >/etc/issue.net <<-EOF
Hello there. This file was built on $DATE
You have reached my system. Nice, isnt it?
EOF

To quote bash(1)
"If the redirection operator is <<-, then all leading tab
characters are stripped from input lines and the line con-
taining delimiter. This allows here-documents within
shell scripts to be indented in a natural fashion."





- --

Lew Pitcher, IT Specialist, Enterprise Data Systems
Enterprise Technology Solutions, TD Bank Financial Group

(Opinions expressed here are my own, not my employer's)
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ray <nospam@example.com> wrote:
> The question is - is that the shell (bash) or ??? that supports that
> function?

It is actually a generic shell function, any self-respecting shell
should support it (and that includes bash, tcsh, ksh and even the
original Bourne shell:
<<[-]word The shell input is read up to a line that is the
same as word, or to an end-of-file. The resulting
document becomes the standard input. If any
character of word is quoted, no interpretation is
placed upon the characters of the document;
otherwise, parameter and command substitution
occurs, (unescaped) \new-line is ignored, and \
must be used to quote the characters \, $, `, and
the first character of word. If - is appended to
<<, all leading tabs are stripped from word and
from the document.
from the man page for the Bourne shell on a HP-UX - real Unix SystemV -
workstation).

As people already told you, it's called a "here document", as it was
invented to put the input for a command INTO the script itself (the
input document is "here").
--
************************************************** ******************
** Eef Hartman, Delft University of Technology, dept. EWI/TW **
** e-mail: E.J.M.Hartman@math.tudelft.nl, fax: +31-15-278 7295 **
** snail-mail: P.O. Box 5031, 2600 GA Delft, The Netherlands **
************************************************** ******************

On 2005-06-07, ray <nospam@example.com> wrote:
> simple question...
>
> cat << EOF
> foo
> bar
> EOF
>
> echos foo and bar...
>
> The question is - is that the shell (bash) or ??? that supports that
> function?

Yes, bash and other scripting languages. Here's some good info:

http://linuxcommand.org/wss0030.php

nb

On Tue, 07 Jun 2005 15:55:30 -0400, Lew Pitcher <Lew.Pitcher@td.com> wrote:
>
> FWIW, in usenet posts and emails, I typically indent code examples by
> two characters to highlight them /as code examples/. The indentation (in
> the post) isn't meant to be copied literally.

My apologies, sometimes I shouldn't answer posts half-asleep, but it
might confuse reader if it not work after copy/paste
>
> As for the '-', then
> DATE=`date`
> cat >/etc/issue.net <<-EOF
> Hello there. This file was built on $DATE
> You have reached my system. Nice, isnt it?
> EOF

Would've used echo, but then, with so many ways to do things,
'correct' defined as 'does it do the expected?' Not style.
I tend to think of 'here' documents as data arrays, similar
syntax to reading a file in shell script. Only because that's
the sort of utility I been writing lately. Didn't pick on
your backticks )

--Grant.

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Grant Coady wrote:
> On Tue, 07 Jun 2005 15:55:30 -0400, Lew Pitcher <Lew.Pitcher@td.com> wrote:
>
>>FWIW, in usenet posts and emails, I typically indent code examples by
>>two characters to highlight them /as code examples/. The indentation (in
>>the post) isn't meant to be copied literally.
>
>
> My apologies, sometimes I shouldn't answer posts half-asleep, but it
> might confuse reader if it not work after copy/paste

No problem. No offence meant and none taken.

I hadn't thought of the cut'n'paste angle. Perhaps I had better put sentinals
around code examples to facilitate that sort of thing.

>
>>As for the '-', then
>> DATE=`date`
>> cat >/etc/issue.net <<-EOF
>> Hello there. This file was built on $DATE
>> You have reached my system. Nice, isnt it?
>> EOF
>
>
> Would've used echo, but then, with so many ways to do things,
> 'correct' defined as 'does it do the expected?' Not style.
> I tend to think of 'here' documents as data arrays, similar
> syntax to reading a file in shell script. Only because that's
> the sort of utility I been writing lately. Didn't pick on
> your backticks )

Again, not a problem. I was trying for a /simple/ example to show that shell
variable substitution was handled in the here document. P'haps I didn't pick
as transparent an example as I should have.

I should have pointed the OP at an article I wrote for The Linux Gazette that
had a good example of the use of a here document. In
http://linuxgazette.net/105/pitcher1.html I have a piece of shell script that
updates my ISP's webserver with my homepage. The script invokes FTP with a
here document (crude, but it does what I wanted) to transfer the built html
page to my ISP's server. The FTP script looks like
#-------------code example----------
#<--- left margin ------

TEMPFILE=`/usr/bin/mktemp /tmp/$1=XXXXXX` || exit 2

# ... elided logic to build html homepage into $TEMPFILE

ISP_ADDRESS=webserver.isp.com
ISP_USERID=username
ISP_PASSWD=password

/bin/ftp -n <<STOP
open $ISP_ADDRESS
user $ISP_USERID $ISP_PASSWD
ascii
put $TEMPFILE index.htm
bye
STOP

#<--- left margin ------
#-------------code example----------


> --Grant.


- --
Lew Pitcher

Master Codewright & JOAT-in-training | GPG public key available on request
Registered Linux User #112576 (http://counter.li.org/)
Slackware - Because I know what I'm doing.
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Lew Pitcher <Lew.Pitcher@td.com> trolled:

pgp trash troll delete

> -----BEGIN PGP SIGNED MESSAGE-----
> Hash: SHA1
>
> ray wrote:
>> simple question...
>>
>> cat << EOF
>> foo
>> bar
>> EOF
>>
>> echos foo and bar...
>>
>> The question is - is that the shell (bash) or ??? that supports that
>> function?
>>
>> Simple question I'm sure, but googling for << doesn't work....
>>
>>
>> Either zsh supports that as well or it's not bash... I'm confused.
>
> It's called a "here document". Google for that term, and you'll get a
> much better explanation than I can give.
>
> But, in brief
> it is a feature of the shell; bash supports it, and (apparently) so does
> zsh.
>
> The construct
> <<something
> data
> data
> something
>
> tells the shell to collect all the lines following the <<something, up
> to but not including the trailing 'something' and feed that data into
> the processes stdin.
>
> Shell variable expansion will be performed, given the suitable set up of
> your shell.
>
> So, for instance,
> DATE=`date`
> cat >/etc/issue.net <<EOF
> Hello there. This file was built on $DATE
> You have reached my system. Nice, isnt it?
> EOF
>
> will expand the $DATE field, and copy the resulting text into your
> /etc/issue.net file
>
> See bash(1) for details
> You might also read http://www.faqs.org/docs/abs/HTML/here-docs.html
>
>
>
>
> - --
>
> Lew Pitcher, IT Specialist, Enterprise Data Systems
> Enterprise Technology Solutions, TD Bank Financial Group
>
> (Opinions expressed here are my own, not my employer's)
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> Version: GnuPG v1.2.4 (MingW32)
>
> iD8DBQFCpcxBagVFX4UWr64RAtZOAKDaUuMJ0VlaDKv0blEIHx zAUeKp5wCfciyr
> t5H9+178SZVGPkQggFx/gFw=
> =gc6C
> -----END PGP SIGNATURE-----
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