Variables, using $ and ${ }_"other words"

[Manuales]

Hi ..
I have a value kept in $file_galaxy variable but i need to use same variable with date format as follows: $file_galaxy_`date +"%Y%m%d"

but it does not work !!!!
i have tested:
$file_galaxy_`date +"%Y%m%d"
$(file_galaxy)_`date +"%Y%m%d"
${file_galaxy}_`date +"%Y%m%d"
`file_galaxy`_`date +"%Y%m%d"

and any of above shown work !!!!

please help 1!!
I'm using sh and ksh ...

I only obtain: _20060612 or 20060612
thanks ....

[Pete Randall · Accepted solution]

It looks like you've got your back ticks reversed to forward ticks. Try
$file_galaxy_`date +"%Y%m%d`


Pete

[Pete Randall]

While I was waiting for the submit it occured to me that the "_" character is probably not part of the original variable file_galaxy. Try

${file_galaxy}_`date +"%Y%m%d`


Pete

[Manuales]

sorry i forget to put "`" at the end of the variables:

$file_galaxy_`date +"%Y%m%d"`
$(file_galaxy)_`date +"%Y%m%d"`
${file_galaxy}_`date +"%Y%m%d"`
`file_galaxy`_`date +"%Y%m%d"`

but any way they do not work ..!!!! :'(

help !!!
SOS !!!!

[Sandman!]

the syntax should be...

# echo ${file_galaxy}_`date +"%Y%m%d"`
or
# echo ${file_galaxy}_$(date +"%Y%m%d")

in each of your cases, you are missing the variable-delimiting braces, ${file_galaxy}, and the terminating single-tick for command substitution i.e. `date +"%Y%m%d"`

~cheers

[Ken Grabowski]

Not sure why your third example did not work, unless you forgot to close the single quote.

I wrote:
#!/usr/bin/sh

file_galaxy="testfile"

print $file_galaxy

date=`date +"%Y%m%d"`

print $date

print ${file_galaxy}_`date +"%Y%m%d"`

and got:
./junk.sh
testfile
20060612
testfile_20060612

when run.
I used 11.11 for the test.

[Gregory Fruth]

Try ${file_galaxy}_`date +"%Y%m%d"`

All of your examples are missing the final
backtick (`). Also,

Example 1 doesn't work because the shell
thinks the second "_" is part of the
variable name.

Example 2 doesn't work because $(...) runs
the ... as a command.

Example 4 doesn't work because `...` runs
the ... as a command.

[A. Clay Stephenson]

Do something like this:

NEWVAR=${file_galaxy}_$(date '+%Y%m%d')

echo "NEWVAR = \"${NEWVAR}\""

[James R. Ferguson]

Hi Manuales:

These are ambiguous variable names. Is the underscore part of the name or is it just another part of the overall interpreted string?

Consider the first one: $file_galaxy_`date +"%Y%m%d"

If I add the closing backtick:

# echo $file_galaxy_`date +"%Y%m%d"`
sh: file_galaxy_: Parameter not set.

Thus, the shell "thinks" that the variable to be interpreted is named "file_galaxy_". Is that what you meant, or did you mean "file_galaxy"?

# echo ${file_galaxy}_`date +"%Y%m%d"`
sh: file_galaxy: Parameter not set.

NOTE that the second time I enclosed the variable name in braces -- {}

This informs the shell of the exact variable name without ambiguity.

Regards!

...JRF...

[A. Clay Stephenson]

If you get into the habit of enclosing all shell variables in {}'s even in the cases where they are not absolutely required, you will avoid many problems. I always prefer code (even in my head) that does not branch.

[Manuales]

THANKS TO ALL:
It worked with this one:

${file_galaxy}_$(date +"%Y%m%d")


i do not know why this do not work with "`" at the beggining and the end of the variable ..


ANY WAY THANKS TO ALL FRIENDS °!!!!!!

[Bill Hassell]

And if you check the man pages for ksh and the HP POSIX shell sh-posix, you'll see that backticks (reverse apostrophes or grave accents) are deprecated (or not recommended). There several reasons:

1. The back tick ` looks too much like a forward tick ' (apostrophe)

2. Back ticks can easily be missed in printed text, especially on a fax.

3. Back ticks cannot be nested.

The preferred coding is to use $(commands). Thde $() construct can easily be nested, something like this:

# lvdisplay $(bdf /tmp|tail -1| cut -f1 -d\ )|grep "^LV"
LV Name /dev/vg00/lvol4
LV Permission read/write
LV Status available/syncd
LV Size (Mbytes) 80

This command finds the mountpoint source for /tmp using bdf, then extracts it with cut, uses the value as an argument to lvdisplay and grep grabs all the LV lines. Not possible with backticks.

[Bill Hassell]

Ooops, I showed my interim tests. Here was the desired result:

echo $(lvdisplay $(bdf /tmp|tail -1| cut -f1 -d\ )|grep "^LV Size")|awk '{print $NF}'

which shows the Mbyte size for /tmp. The LV Size line contains the Mbytes number at the end. (somewhat impractical example but shows how $(...$(...)) can be nested.