expr to translate the date command

 
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# 1  
Old 03-02-2011
expr to translate the date command { solved }

Use and complete the template provided. The entire template must be completed. If you don't, your post may be deleted!

1. Write a script called "tod" that will display the time of day in am or pm notation rather then the 24 hour clock time. Use expr to convert from 24-hour clock time.
Use either (if) or (case) statement. Use the standard, unmodified output from the date command for this exercise.



2. Relevant commands, code, scripts, algorithms:
date, cut and expr

3. The attempts at a solution (include all code and scripts):#!/bin/sh -xv
# this is the date script
#this will change the 24hr to 12hr
#
#
let i=$"`date +%H`"
let MIN=$"`date | cut -c15-19`"
if [ $i -gt 12 ]
then
`expr $i -12`
echo " $i:$MIN"
fi
esle
echo "$i:$MIN"
fi
########################################
I've also used
########################################
HR=$"`date | cut -c1-2`"
MT=$"`date | cut -c15-19
NEWHR=$"`expr $HR - 12`"
if [ $HR -le 12 ]
then
echo "$HR:$MT"
esle
echo " $NEWHR:$MIN"
fi
########################################
and
########################################
HR=$"`date | cut -c1-2`"
MT=$"`date | cut -c15-19
NEWHR="`expr $HR - 12`

case $NEWHR
in
24) `expr $NEWHR -12`;;
echo "$NEWHR:$MT"
23) `expr $HR -12`;;
and so on till
*) to eat up the rest
esac



4. Complete Name of School (University), City (State), Country, Name of Professor, and Course Number (Link to Course):
Washtenaw community college, Washtenaw MI, Phil Geyer, CIS 221.


Any help would be great this has been driving me nuts all spring break. Note : I'm using bash shell, the expr is the thing going wrong it keeps giving me a non-numeric argument error.

Note: Without school/professor/course information, you will be banned if you post here! You must complete the entire template (not just parts of it).

---------- Post updated at 07:44 PM ---------- Previous update was at 07:39 PM ----------

#!/bin/sh -xv
# this is the date script
#this will change the 24hr to 12hr
#
#
let i=$"`date +%H`"
+ date +%H
+ let i=$19
./datt: let: not found
let MIN=$"`date | cut -c15-19`"
+ date
+ cut -c15-19
+ let MIN=$43:47
./datt: let: not found
if (\ [ "$i" -gt 12 \) -a \( "$i" -eq 24 \) ]
then
./datt: syntax error at line 10: `then' unexpected
I figured it out thank you for helping me
code:
this will change the 24hr to 12hr
#
#
HR=$"`date +%H`"
MIN=$"`date +%M`"
SEC=$"`date +%S`"
NEWHR=$"`expr $HR - 12`"
#
#
#
if [ $HR -gt 12 ]
then
echo "$NEWHR:$MIN:$SEC pm"
else
echo "$NEWHR:$MIN:$SEC am"
fi

Last edited by linuxtraining; 03-02-2011 at 10:47 PM.. Reason: left out a $
# 2  
Old 03-02-2011
There needs to be spaces between everything in expr. 3 -12 is invalid, 3 - 12 is okay.

That aside your script can be made a lot better in other ways. You don't need to be doing cut all the time to do simple string processing, that's really slow and difficult.
Code:
#!/bin/bash

T="am"
# One way to split strings
read H M S <<<$(date +'%H %M %S')
# Another:
# STR=`date '+%H %M %S'`
# H="${STR:0:2}"
# M="${STR:3:2}"
# S="${STR:6:2}"

H="${H##0}"     # Strip leading zero

if [[ "${H}" -gt 12 ]]
then
        T="pm"
        H=`expr $H - 12`
fi

# printf makes it easy to put them all back together.
# We print the first one as digits, so it can add a leading zero,
# but the rest we just print as strings.
printf "%02d:%s.%s %s\n" $H $M $S $T

# 3  
Old 03-02-2011
thank you for your reply Corona I get a error
[[: H##0: expression recursion level exceeded (error token is "H##0")
But thank you for taking the time to help. When I run this in debugging mode it shows the H=`expr` to be null value this is a problem that I have been fighting for the last week. I can't get the expr command to realize that it has a value for some reason.

---------- Post updated at 08:17 PM ---------- Previous update was at 08:15 PM ----------

./datt3: line 5: syntax error near unexpected token `<<<$'
./datt3: line 5: `read H M S <<<$(date +'%H %M %S')'
also those two errors are new.
# 4  
Old 03-02-2011
Be sure you entered the code I gave you word for word, letter for letter, keystroke for keystroke.

Are you sure you're using bash? bash is not just any shell.
# 5  
Old 03-02-2011
Yes. I even made sure by doing echo $SHELL and it printed bash.
The school server is a little weird I think they don't have somethings active on it until we get in the 226 class so that maybe the reasoning for the errors we encountered. Thank you very much for all you help though. I'm doing the same problem now using the case statement. ( just because I love writing scripts and Linux)
# 6  
Old 03-02-2011
What does bash --version do.

---------- Post updated at 08:17 PM ---------- Previous update was at 08:16 PM ----------

If you can't use <<< because you have a ridiculously old version of bash, you can do
Code:
date +'%H %M %S' > /tmp/$$
read H M S </tmp/$$
rm -f /tmp/$$

# 7  
Old 03-02-2011
GNU bash, version 2.05.0(1)-release (sparc-sun-solaris2.9)
Copyright 2000 Free Software Foundation, Inc.
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