Single line insert to the start of a file

darklord_999 has asked for the wisdom of the Perl Monks concerning the following question:

I have a 2 files as below

File1:

HEADER
XXXXX
YYYYY
ZZZZZ
EOF
[download]

File2:

AAAAA
BBBBB
CCCCC
DDDDD
EOF
[download]

How can I get the first line from File1 and insert it into the first line of File2?File 2 ultimately should look like below:

HEADER
AAAAA
BBBBB
CCCCC
DDDDD
EOF
[download]

Is there a single liner which can do this ?

Comment on Single line insert to the start of a file Select or Download Code

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Re: Single line insert to the start of a file by aaron_baugher (Curate) on Aug 16, 2012 at 09:57 UTC
Assuming a *nix system, and the existence of a real-world problem to be solved rather than a homework problem in a particular language: `head -1 file1 >/tmp/file.$$; cat file2 >>/tmp/file.$$; mv /tmp/file.$$ file2` Aaron B. Available for small or large Perl jobs; see my home node.	[reply] [d/l]
Re: Single line insert to the start of a file by Anonymous Monk on Aug 16, 2012 at 07:18 UTC
See get n lines before or after a pattern, Re: modifying a file with regex!, perlintro, open, readline, rename	[reply]
Re: Single line insert to the start of a file by cheekuperl (Monk) on Aug 16, 2012 at 07:38 UTC
How big is your file? You can also try reading the file into an array, then unshift new entry to that array and write it back to the file :P	[reply]
Re: Single line insert to the start of a file by trizen (Hermit) on Aug 16, 2012 at 09:52 UTC
`perl -MTie::File -e'tie@a,"Tie::File","f2.txt";unshift@a,scalar<>'<f1.txt`	[reply] [d/l]
Re: Single line insert to the start of a file by kcott (Archbishop) on Aug 16, 2012 at 10:14 UTC
I suspect any one-liner is going to be somewhat unwieldy. Here's one using Tie::File: `ken@ganymede: ~/tmp $ cat > pm_add_header_1 HEADER XXXXX YYYYY ZZZZZ ken@ganymede: ~/tmp $ cat > pm_add_header_2 AAAAA BBBBB CCCCC DDDDD ken@ganymede: ~/tmp $ perl -Mstrict -Mwarnings -MTie::File -e 'my @f; my $i = 0; tie @{$f[ +$i++]}, q{Tie::File}, $_ or die $! for @ARGV; unshift @{$f[1]}, $f[0] +[0];' pm_add_header_1 pm_add_header_2 ken@ganymede: ~/tmp $ cat pm_add_header_2 HEADER AAAAA BBBBB CCCCC DDDDD ken@ganymede: ~/tmp $` [download] -- Ken	[reply] [d/l]
Re: Single line insert to the start of a file by aitap (Curate) on Aug 16, 2012 at 08:24 UTC
Use `-p` flag to run your code in the loop: `LINE: while (<>) { ... # your program goes here } continue { print or die "-p destination: $!\n"; }` [download] and `-i` flag to edit files in-place (see perlrun for more). Use $. to check the line number. Define `BEGIN{}` to read the header, then write it in the main loop: `perl -pi -e'BEGIN{$HEAD=shift@ARGV;open(HEAD);$main::head=<HEAD>}$_=$m +ain::head.$_ if $.==1' header-file file-to-be-edited` [download] Perhaps avoiding the `-p` will be more efficient, but not so compact: `perl -e'($HEAD,$FILE)=@ARGV;open(HEAD);open(FILE);open($f,">$FILE.$$") +;print $f scalar <HEAD>,<FILE>;rename "$FILE.$$","$FILE"' header-file + file-to-be-edited` [download] Warning: both of the one-liners use somewhat deprecated one-argument open and barewords as filehandles. Sorry if my advice was wrong.	[reply] [d/l] [select]