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Shell Printf command , a little more dynamic..


 
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# 1  
Old 02-04-2013
Shell Printf command , a little more dynamic..

A big hello to everyone tagged to this site of knowledge . This is the first post of mine and I am looking forward to an enjoyable stint in this forum where I get to know a lot of new ideas and share whatever knowledge (its not much though Smilie ) I have acquired throughout my career so far with y'all.

To start of , I am , in a sort of stuck in a strange situation.
The requirement is to format a string to a precision , which is will be dynamic .

Lets say the string's 976461 , and we have to format it to a precision of 10 , and LEFT PAD it with zero's. So the output would be 0000976461 .

What I did is to store the precision in a Shell variable (say a ) using the following code :
Code:
a=10

and the string in another Shell variable b using :
Code:
b=976461

and use the printf command to format the string to the precision stored in variable a , and finally write the output to variable c using
Code:
c=` printf "%0'$a'd" $b`

Now , when I echo the value of c, it showing 000976,461.

Can anyone help me with this ?

Thanks
Kumarjit.

Last edited by Scrutinizer; 02-04-2013 at 06:02 AM.. Reason: code tags
# 2  
Old 02-04-2013
Is this exactly how you wrote it? My shell gives an error due to the quoting. Which shell are you using? This works in dash, a mostly posix sh:

Code:
$ a=10 b=976461
$ c=$(printf "%0${a}d" "$b")
$ echo "$c"
0000976461

# 3  
Old 02-04-2013
Or:
Code:
c=$(printf "%0*d" "$a" "$b")

This User Gave Thanks to Scrutinizer For This Post:
# 4  
Old 02-04-2013
Thanks a ton to you both ( neutronscott and Scrutinizer ), you guys got crazy skills .....

BTW, I am using Korn Shell.

To be very honest , I havent been into Shell scripting for a long period of time, but am keen to know how each of yours codes work .

@neutronscott----firstly what does ${a} in the expression "%0${a}d" stand for , and how different is it from using a blatant "%0$ad" or something like "%0'$a'd"
What I meant to ask is the significance of the {} while invoking a shell variable ?

@Scrutinizer---- I have to admit I dont even have any questions to ask BECAUSE I COULDNT MAKE THE HEADS OR TAILS OF WHAT YOU WROTE, but it works magic .
Could you please explain what your code does and the significance of "*" in the printf command ?

Thank you guys,
Kumarjit.
# 5  
Old 02-04-2013
Hi Kumar, from man printf:

Quote:
A field width or precision may be `*' instead of a digit string. In this case an argument supplies the field width or precision.
So

Code:
printf "%0*d" 10 "$b"

works like
Code:
printf "%010d" "$b"

This User Gave Thanks to Scrutinizer For This Post:

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