CODEWITHSUNDEEP
bashawkswap
André Soares
André Soares

Reputation: 309

swap the first two lines in all files in a folder

I want to swap the first two lines in all files in a folder and save that over the existing files, keeping file names as before.

What I have:

awk '{getline x;print x}1' *.map.txt

Can this be written only for the first two lines?

What this does is just print in the terminal all the outputs for each file.

Upvotes: 0

Views: 162

Answers (3)

Aaron
Aaron

Reputation: 24812

You can do it with sed :

sed '1{h;d};2{x;H;x}'

Explanation :

1 and 2 are line number selectors ; the following commands will only be executed on those lines
h puts the current line in the 'hold' buffer
d deletes the line
x swaps the hold buffer with the current line
H appends the current line to the hold buffer

Test run with GNU sed :

$ mkdir test35597922
$ echo """line1
> line2
> line3""" > test35597922/file1.txt
$ echo """line1
line2
line3""" > test35597922/file2.txt
$ sed -i '1{h;d};2{x;H;x}' test35597922/*
$ ls test35597922/
file1.txt  file2.txt
$ cat test35597922/file1.txt
line2
line1
line3
$ cat test35597922/file2.txt
line2
line1
line3

If you can't use the 'in place' -i flag and want to edit the files, you can process as follows :

for file in test35597922/*; do
  sed '1{h;d};2{x;H;x}' $file > tmp_file
  mv tmp_file $file
done

On some systems it could be done in one action (sed '1{h;d};2{x;H;x}' $file > $file) but that will fail on others, the file being overwriten before it has entirely been read.

Upvotes: 1

sat
sat

Reputation: 14949

Another sed:

sed -e '1{N;s/^\(.*\)\n\(.*\)/\2\n\1/;}' file

Use -i to affect the changes in file.

If you don't have -i option, try below way.

sed -e '1{N;s/^\(.*\)\n\(.*\)/\2\n\1/;}' file > new_file && mv new_file file

Upvotes: 0

gniourf_gniourf
gniourf_gniourf

Reputation: 46873

With ed (and Bash):

for file in ./*; do
    [[ -f $file ]] || continue
    ed -s "$file" <<< $'1m2\nw\nq\n'
done

The ed command that does the trick is: 1m2 that selects the first line and moves it to the 2nd line. If you have files with 0 or 1 lines, you'll see some harmless ? on standard error. You can redirect them to /dev/null by appending 2> /dev/null after the done.

Upvotes: 1

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