Perl inline replace only on 1st line

Shell Programming and Scripting
1

I have file file_1.out which contains the data below

<tr> MAIL # 1 TO src_1 </tr> 
<tr><td class="hcol">col_id</td> <td class="hcol">test_dt</td> <td class="hcol">user_type</td> <td class="hcol">ct</td></tr> 
<tr><td class="bcol">1</td> <td class="bcol">2012-09-20</td> <td class="bcol">A</td> <td class="bwcol">15</td></tr> 
<tr><td class="bcol">1</td> <td class="bcol">2012-09-20</td> <td class="bcol">B</td> <td class="bwcol">90</td></tr> 
<tr><td class="bcol">1</td> <td class="bcol">2012-09-20</td> <td class="bcol">C</td> <td class="bcol">6</td></tr> 
<tr><td class="bcol">1</td> <td class="bcol">2012-09-20</td> <td class="bcol">D</td> <td class="bcol">4</td></tr>

How can I replace only the first line with the following:

<tr><td colspan="4" class="hcol"> MAIL # 1 TO src_1 </td></tr> 
<tr><td class="hcol">col_id</td> <td class="hcol">test_dt</td> <td class="hcol">user_type</td> <td class="hcol">ct</td></tr> 
<tr><td class="bcol">1</td> <td class="bcol">2012-09-20</td> <td class="bcol">A</td> <td class="bwcol">15</td></tr> 
<tr><td class="bcol">1</td> <td class="bcol">2012-09-20</td> <td class="bcol">B</td> <td class="bwcol">90</td></tr> 
<tr><td class="bcol">1</td> <td class="bcol">2012-09-20</td> <td class="bcol">C</td> <td class="bcol">6</td></tr> 
<tr><td class="bcol">1</td> <td class="bcol">2012-09-20</td> <td class="bcol">D</td> <td class="bcol">4</td></tr>

For now I am replaciong inline:

find file_1.out -type f | xargs perl -pi -e 's/<tr> MAIL #/<tr><td colspan="4" class="hcol"> MAIL #/gi; s/ <\/tr>/<\/td><\/tr>/gi'

But I dont want to use the MAIL tag in the command, if it appears agian some where in the file it does'nt work.

Thanks for your help.

2

This should replace only on first line in each file:

find file_1.out -type f | xargs perl  -pi -e '$.==1&&s/<tr> MAIL #/<tr><td colspan="4"  class="hcol"> MAIL #/gi; s/ <\/tr>/<\/td><\/tr>/gi'
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3

Similarly how can we select only the last line?

4

It requires some changes to the way you edit the file (you have to load whole file as one line):

find file_1.out -type f | xargs perl -i -p0e 's/<tr> MAIL #(.*)$/<tr><td colspan="4" class="hcol"> MAIL #$1/gi; s/ <\/tr>/<\/td><\/tr>/gi'
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5

Or:

| xargs perl -i -pe 'if(eof){s/...........'

Or you may use sed too:
For substituting in first line: sed -i '1s///g'

For substituting in last line: sed -i '$s///g'

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