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    <p>awk is definitely your friend.</p> <p>awk reads a datafile, line-by-line. You don't need/want to have any kind of loop structure (unless you're getting very advanced). </p> <pre><code>awk '{print $0}' inFile </code></pre> <p>Is all you need to read each line of a file and print it out (it will go to your screen, so don't do a big file)</p> <p>note that I used <code>$0</code> to indicate 'the whole line of data'.</p> <p>Awk also has variables to refer to each field of data, you use values like <code>$2</code> to print the 2nd field in the file.</p> <blockquote> <p>I want to replace the digits by letters according to column 5th &amp; 6th. So what I want is to replace 0 with T T (if the 5th column is T) and 2 by C C (if the 6th column is C) and 1 with T C (if the 5th and 6th columns are T and C respectively) and I want to change -1 to ? ? or ! !</p> </blockquote> <p>So for your problem, you want to test each line, test certain fields and set new values.</p> <pre><code>awk 'NR&gt;1{ # replace 0 with T T (if the 5th column is T) if ($5 == 0) $5="TT" # and 2 by C C (if the 6th column is C) if ($6 == 2) $6="CC" # and 1 with T C (if the 5th and 6th columns are T and C respectively) if ($5 == "T" &amp;&amp; $6 == "C") $1="1" }' inputFile | sed 's/TT/T T/; s/CC/C C/' </code></pre> <p>To change all fields after a certain field, incorporate this code as needed,</p> <pre><code>awk 'NR&gt;1{ # replace 0 with T T (if the 5th column is T) if ($5 == 0) { for (i=5; i&lt;=NF;i++) { printf("T ") } printf("\n") } ...... </code></pre> <p>}' inputfile ...</p> <p>The <code>NR&gt;1</code> means only processes line numbers greater than 1.</p> <p>Note that we're using simple logic to implment your tests. it is easy to add more and more. Recall that many times it makes sense to use 'layered' logic <code>if ($5==0) { ... } else if ($5 == 1) { ....}</code></p> <p>The one problem is your requirement to output 'C C', for example. When you do something like `$5="C C" in awk, awk will recalibrate its field numbers, so $5 will be C and $6 will be C, not the value that was there before. </p> <p>I have taken the short-cut of printing 'CC', and then using sed at the the end to create the 'C C' values that your specfication indicates.</p> <p>I'm not sure how to deal with </p> <blockquote> <p>and I want to change -1 to ? ? or ! !</p> </blockquote> <p>as it has to be one or the other, and I'm not sure what field you want to operate on. Use the above code as a guide. If you get stuck, post a new question with sample input data, expected output, current output and the code you are using.</p> <p>I hope this helps.</p>
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    1. POHow to replace some digits with letters in each line of a file (according to the letter that exist in column 5th and 6th of that line)?
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    1. COI think I asked my question bad or you miss understood me some how! I want to replace from column 7th to the end! and I want to replace them according to what letter exist in column 5 and 6! so I want if it's 0 be replace by $5 $5(I mean two repetition of column 5th) and if it's 1 replace by $5 $6 and if 2 replace by $6 $6 and -1 by ? ?
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    2. COthanks I'm try hard now :)
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    3. COyou can understand how awk works now from my example? I'll add one more bit. See added sample code. Good luck.
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