Wednesday, November 30, 2011

Perl Power - Sequential Iteration in shell scripts

Lets say you want to process a bunch of files containing a numeric sequence like "inventory000297.txt" through "inventory000302.txt". You would like to print the following:

inventory000297.txt
inventory000298.txt
inventory000299.txt
inventory000300.txt
inventory000301.txt
inventory000302.txt

I did not see a simple way to do this using a plain shell script, but adding some perl is a different story...

for F in $(perl -e 'foreach $num (297 .. 302) {printf("%s%06i%s\n","inventory",$num,".txt");}')
do
    echo ${F}
done

Notes to keep in mind:
  • $( ) contains the perl one-liner that generates the output to print
  • The perl script is between the single quotes
  • The foreach loop block is within braces { }
  • The numerical range is in parenthesis ( 297 .. 302 ), change this as necessary
  • The printf has 3 format specifiers:

    %s corresponds with "inventory", change prefix as necessary

    %06i corresponds with $num, a fixed width 6 digit integer, change as necessary

    %s corresponds with the ".txt", change extension as necessary






Adjust the size of your sequence number - if 15 digits is needed you would use %015i for the format. That leading 0 says fill in with leading zeros on output to match the specified width.

Enjoy!

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