UNIX for Dummies Questions & Answers

How about

Code:

cat<<eoi>inpfile Some standard lines of the program that is going to execute inpfile .... 
$key 
$(< geom.txt)
Some other standard lines...
eoi

One reason might be that even though it will work in bash and ksh93, it is not POSIX compliant and so for portability it would be best to use $(cat file)

Scrutinizer, isn't that a command substitution form?

If so isn't it suppose to work on all POSIX shell?

Yes. However, there is no need to save the contents of file in a variable. Just use the line:

Code:

$(cat geom.txt)

in the here document instead of:

Code:

geo=$(cat geom.txt)

before the here document and:

Code:

$geo   # inserts contents of geom.txt here

in the here document.

---------- Post updated at 12:35 ---------- Previous update was at 12:22 ----------

No. The command substitution $(< file) as defined by the standard is the equivalent to the command:

Code:

< file

executed in a subshell and the standard output of that command (which would be nothing) would be the expansion of the command substitution.

In theory, I'm not sure that the standards allow shells to actually produce any output in this case, but since it isn't the type of command you would expect to find in a standards conforming shell script, no one has complained. If someone did complain that a shell was non-conforming because of this construct, I'm sure the Austin Group would issue an interpretation saying that the standard is "clear and wrong" and either specify the current behavior in the next revision of the standard or explicitly state that the behavior is unspecified in this case (which would allow shells to continue to provide this extension).

But please take Rudi's solution and save memory!
The backticks even work in an old Unix shell:

Code:

cat<<eoi>inpfile
Some standard lines of the program that is going to execute inpfile ....
$key
`cat geom.txt`
Some other standard lines...
eoi

or, without a here document (again goes to memory),

Code:

echo "\
Some standard lines of the program that is going to execute inpfile ....
$key
`cat geom.txt`
Some other standard lines...
" > inpfile

Or

Code:

{
echo "\
Some standard lines of the program that is going to execute inpfile ....
$key"
cat geom.txt
echo "\
Some other standard lines...
"
} > inpfile