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changing the first number of every line

by jinism (Initiate)
on Nov 21, 2012 at 12:55 UTC ( #1004912=perlquestion: print w/replies, xml ) Need Help??
jinism has asked for the wisdom of the Perl Monks concerning the following question:

Dear Monks,

I am relatively new to perl and would like to request for a code that would enable me to change the first number of a line of vectors for all lines in the txt file.

An example of the vectors looks like this:

0 1:120.000000 2:0.000000 3:120.000000 4:262.000000 5:120.000000 6:349.000000

Every line starts with 0, and i would like to replace that 0 with 1

I have around 100 of these lines in my file and any help would be greatly appreciated!

  • Comment on changing the first number of every line

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Re: changing the first number of every line
by roboticus (Chancellor) on Nov 21, 2012 at 13:15 UTC


    You can get a good start with that by reading perlintro and look over perlfaq5, especially the section "How do I change, delete, or insert a line in a file, or append to the beginning of a file?".


    When your only tool is a hammer, all problems look like your thumb.

Re: changing the first number of every line
by choroba (Chancellor) on Nov 21, 2012 at 13:14 UTC
    perl -i~ -p -e 's/^0/1/' *.txt
    -i changes the files, backups are created with the ~ appended
    -p prints each line after applying the code.
    The code just replaces 0 at the beginning of a line with 1.
    لսႽ ᥲᥒ⚪⟊Ⴙᘓᖇ Ꮅᘓᖇ⎱ Ⴙᥲ𝇋ƙᘓᖇ
Re: changing the first number of every line
by ww (Archbishop) on Nov 21, 2012 at 14:58 UTC
        ...and you can get a better start here if you'll read the docs; particularly, On asking for help and How do I post a question effectively?.
    Despite Parson choroba's generous response, this is NOT code-a-matic. We try to help those like yourself -- "new to perl" -- by helping them learn; not by solving their problems. So next time you have a problem like this; try to organize your thoughts about how you'd do the job on paper, and then, using perldoc -f function and the fine Tutorials here, try to come up with code to solve your quandry.

    If it works, you've really learned something; if it doesn't, and you can't figure out "why," then by all means, come back with the issue, your code (and data; each wrapped in <c>...</c> tags), an explanation of how your code fails to satisfy your intent, and verbatim quotes of any error messages or warnings.

    P.S. use strict; use warnings; or a recent enough version of Perl that invoking the version (for example, use 5.014;) does so for you. Those pragmas alone will help you find many sneaky little mistakes (to say nothing of big ones.

    PPS: If the solution choroba provided doesn't work for you, check that the quoting used is that required by your system -- windoze won't like what you've been given.

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