On 2017 Jan 10 23:56:16, you wrote to Janis:

 JS> I know that I can specify a DOY (Day of Year) variable in a bash file
 JS> as "DOY=$(date +%j)". But, I would only want the variable to express
 JS> the last two digits of DOY. So... 010 would be expressed as 10 and 165
 JS> would be expressed as 65, etc.

 JS> I looking at grabbing a zipped file with a filename of filename.znn
 JS> where "nn" is the DOY minus the first digit.

i'm guessing that you're looking for a specific file of that naming format? i
went another way and simply extract (after making sure there's only one that
fits the name format) foo.z*...

but see how this fits... we're going to use the "${parameter:offset:length}"
substring method with a little twist...


==== Begin "doytest"  ====
#!/bin/bash

DOY=$(date +%j)
DOYS=$(printf "%02d" ${DOY:${#DOY}<2?0:-2})
printf "DOY=\"$DOY\"     DOYS=\"$DOYS\"\n"

DOY=1
DOYS=$(printf "%02d" ${DOY:${#DOY}<2?0:-2})
printf "DOY=\"$DOY\"     DOYS=\"$DOYS\"\n"

DOY=01
DOYS=$(printf "%02d" ${DOY:${#DOY}<2?0:-2})
printf "DOY=\"$DOY\"     DOYS=\"$DOYS\"\n"

DOY=100
DOYS=$(printf "%02d" ${DOY:${#DOY}<2?0:-2})
printf "DOY=\"$DOY\"     DOYS=\"$DOYS\"\n"

==== End "doytest" ====


since we want only the last two characters, if DOY has a length less than 2,
${DOY: -2} would expand to the empty string. in that situation we want all of
DOY so we use this tricky little beast...

${DOY:${#DOY}<2?0:-2}

what we're doing here is replacing the offset value with another parameter
expansion formula... that formula is

${#DOY}<2?0:

this uses the "?:" ternary "if" operator that can be used in Shell
Arithmetic... we can do this because the offset value is an arithmetic
expression... so if DOY contains less than two characters, "${#DOY}<2", we want
 all of them... "the "?0:" is the check if the result is zero length... now
that we've got the last up to two characters of DOY, we use printf to pad
leading zeros if the result has only one character...


sure "$(date +%j)" returns three characters but the reason i added the rest is
because you might find a use for this in other things where you may put data in
 manually... i did that in the above test script to see what happens with one,
two and three character data strings... i can see a situation where you might
want to add or subtract 1 or maybe 7 to the DOY result if you wanted a file up
to a week newer or older... in fact, this is a pretty good start to the old DOS
 DAYNBR tool used in fidonet for so long...


===== snip =====

Please refer to the Shell Parameter Expansion in the reference manual[1]:

${parameter:offset}
${parameter:offset:length}

Expands to up to length characters of parameter starting at the character
specified by offset. If length is omitted, expands to the substring of
parameter starting at the character specified by offset. length and offset are
arithmetic expressions (see Shell Arithmetic). This is referred to as Substring
 Expansion.

If offset evaluates to a number less than zero, the value is used as an offset
from the end of the value of parameter. If length evaluates to a number less
than zero, and parameter is not '@' and not an indexed or associative array, it
 is interpreted as an offset from the end of the value of parameter rather than
 a number of characters, and the expansion is the characters between the two
offsets. If parameter is '@', the result is length positional parameters
beginning at offset. If parameter is an indexed array name subscripted by '@'
or '*', the result is the length members of the array beginning with
${parameter[offset]}. A negative offset is taken relative to one greater than
the maximum index of the specified array. Substring expansion applied to an
associative array produces undefined results.

Note that a negative offset must be separated from the colon by at least one
space to avoid being confused with the ':-' expansion. Substring indexing is
zero-based unless the positional parameters are used, in which case the
indexing starts at 1 by default. If offset is 0, and the positional parameters
are used, $@ is prefixed to the list.

===== snip =====

[1]
http://www.gnu.org/software/bash/manual/bashr...



full disclosure:
i got the tricky looking parameter expansion formula from this page... i've
also copied some of the relevent text as well as trying to word the explanation
 in my own way and make it easier to understand...
http://stackoverflow.com/questions/19858600/b...
-string


)\/(ark

Always Mount a Scratch Monkey
Do you manage your own servers? If you are not running an IDS/IPS yer doin' it
wrong...
... Although the exit polls say otherwise.
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 * Origin:  (1:3634/12.73)