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for loop with leading zero in bash 3

Terminal - for loop with leading zero in bash 3
for i in {0..1}{0..9}; do echo $i; done
2009-09-18 02:51:12
User: dennisw
Functions: echo
-1
for loop with leading zero in bash 3

Bash 4 will let you do {00..19} to get leading zeros, but Bash 3 doesn't have that feature. This technique gets you partway there (the sequences need be such that the last digit ranges from zero to nine - you can't use this for something like Bash 4's {03..27}, for example). When this limitation is not a problem, you can avoid some complicated string manipulation for concatenating leading zeros.

You can add more digits like this: {0..1}{0..9}{0..9} (ranges from 0 to 99 with up to two leading zeros). To pad with additional zeros:

for i in 000{0..1}{0..9}; do echo $i; done

or

for i in {0..1}{0..9}; do echo "000$i"; done

This is useful for creating values to sort or for creating filenames with a fixed format. Note that this will also work:

touch {0..1}{0..9}

Alternatives

There are 8 alternatives - vote for the best!

Terminal - Alternatives
seq -s " " -w 3 20
printf "%02u " {3..20}; echo
2009-09-18 18:48:41
User: Escher
Functions: printf
Tags: bash strings
0

emulates bash4's "echo {03..20}"

Uses bash3 builtin function printf

Know a better way?

If you can do better, submit your command here.

What others think

I think we can obtain the same result using printf

SIZE=2; BEGIN=0; END=19; CHAR='0'; for i in {${BEGIN}..${END}}; do printf "%${SIZE}i\n" ${i} | tr ' ' ${CHAR}; done
Comment by Gentux 257 weeks ago

@Gentux: Bash won't nest this way: {${BEGIN}..${END}}. Besides, using printf or

var=0000$num; var=${var: -4}

is the kind of "complicated string manipulation" I was referring to (although I rather like that last one - note that the space is required between the colon and the minus sign).

Comment by dennisw 257 weeks ago

Your point of view

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