string manipulation

Shell Programming and Scripting
1

hi all,
i am new to shell scripting and need help.
i have a string that stores the month in Jan/Feb/Mar format. i need to convert it to number like 01 for jan, 12 for dec etc.

i am using the following sed command,

echo "Enter a Month eg. Jan/Feb : "

read MONTHEND

MTS=`echo $MONTHEND | sed 's/Jan/01/'`
MTS=`echo $MONTHEND | sed 's/Feb/02/'`
MTS = `echo $MONTHEND | sed 's/Mar/03/'`
MTS = `echo $MONTHEND | sed 's/Apr/04/'`
MTS = `echo $MONTHEND | sed 's/May/05/'`
MTS = `echo $MONTHEND | sed 's/Jun/06/'`
MTS = `echo $MONTHEND | sed 's/Jul/07/'`
MTS = `echo $MONTHEND | sed 's/Aug/08/'`
MTS = `echo $MONTHEND | sed 's/Sep/09/'`
MTS = `echo $MONTHEND | sed 's/Oct/10/'`
MTS = `echo $MONTHEND | sed 's/Nov/11/'`
MTS = `echo $MONTHEND | sed 's/Dec/12/'`

echo $MTS

But it is only working if i give Dec as input. For other months it is returning the month in words itself. please help and suggest a better way.

2

Take a look at your code again, what is the last action it performs, regardless of the month entered?

Perhaps you need to perform a check for the value of month and make the substitution conditional otherwise the result is always the output of the final line.

3

That's because you are using the $MONTHEND var in each assignment. The last one always gets assigned to MTS. You should change the $MONTHEND to $MTS and start with assigning $MONTHEND to MTS (ie. 1st line => MTS=$MONTHEND)

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4

@rn
thank you very much. that was the precise problem. and your solution worked. thanks again for the quick response.

5

Instead of 12 sed commands:

MTS=$(awk -v m=$MONTHEND 'BEGIN{printf( "%.2i\n",index("  JanFebMarAprMayJunJulAugSepOctNovDec", m )/3 )}')
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6

Alternatively, a case...esac sh statement can be used. No real need to bother with external tools such as sed, awk, et al.

case $MONTHEND in
    Jan) MTS=01;;
    Feb) MTS=02;;
    Mar) MTS=03;;
    ...
    Dec) MTS=12;;
esac

Better yet, you can tell users to stuff it and prompt them thusly:

echo "Enter a two digit month (01-12): "

That last suggestion is a joke ... kinda :wink:

Regards,
Alister

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7

@Franklin52
You are right. Using 1 awk statement instead of 12 sed commands is much more efficient, but could you explain how this command works in this case. I'm sure its pretty simple, but it looks a little complex. Thanks

8 
MTS=$(awk -v m=$MONTHEND 'BEGIN{printf( "%.2i\n",index("  JanFebMarAprMayJunJulAugSepOctNovDec", m )/3 )}')

The index() function returns the index of m (the given month) in the string of the 1st parameter.
The length of the month name is 3 and the index of the 1st month is 3, for the 2nd month 6 etc.

"Jan" gives 3; the month number is 3/3=1
"Feb" gives 6; the month number is 6/3=2
"Mar" gives 9; the month number is 9/3=3
"Apr" gives 12; the month number is 12/3=4

and so on..

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9 
# indexa=($(echo Jan01Feb02Mar03Apr04May05Jun06Jul07Aug08Sep09Oct10Nov11Dec12|sed 's/...../& /g') 
# read -p "Enter a Month eg. Jan/Feb : " mnt
Enter a Month eg. Jan/Feb : Jan
# echo ${indexa[@]}|sed "s/.*$mnt\([0-9]*\).*/\1/"
01

regards
ygemici

10

Just pointing out a minor typo: no doubt you meant 3 instead of 6.

Regards,
Alister

1 Like