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I want to add hashes to all the lines in a regular text file. I'm fine with both the use of terminal and GUI—I just need to get it done.

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2 Answers 2

up vote 23 down vote accepted

You can use sed to do that:

sed -i.bak 's/^/##/' file

This replaces the start of the line (^) with ##.

With the -i.bak switch, sed edits the file in-place, but creates a backup copy with extension.bak.

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+1 This is the first time I encounter this backup method. I always did an inline replace directly: sed 's/^/##/' -i file. In this case, this would be preferred since it cannot go wrong. In other cases, this command can be combined with diff -u file.bak file to see the differences (if necessary, pipe it through less). If it's confirmed to work, the backup can be removed. Otherwise it could be restored with a simple mv file.bak file. –  Lekensteyn Jul 30 '11 at 8:28
Elegant. I was thinking about something like sed 's/^\(.*\)$/##\1/', but this is much nicer. –  arrange Jul 31 '11 at 8:54
Nice one.. I was thinking about suggesting Vim to do this... –  Sathish Aug 6 '11 at 13:28

Here is a solution to this problem using perl

perl -e 'while (<>) {print "##$_"}' < infile > outfile
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The -p switch is also useful: perl -pe 's/^/##/' infile > outfile. (There's also the -i[extension] switch for replacing the target file in-place.) perldoc.perl.org/perlrun.html#%2a-p%2a –  Jukka Matilainen Jul 31 '11 at 7:51

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