How to split a file and keep the first line in each of the pieces?
LinuxBashFileShellTextLinux Problem Overview
Given: One big text-data file (e.g. CSV format) with a 'special' first line (e.g., field names).
Wanted: An equivalent of the coreutils split -l
command, but with the additional requirement that the header line from the original file appear at the beginning of each of the resulting pieces.
I am guessing some concoction of split
and head
will do the trick?
Linux Solutions
Solution 1 - Linux
This is robhruska's script cleaned up a bit:
tail -n +2 file.txt | split -l 4 - split_
for file in split_*
do
head -n 1 file.txt > tmp_file
cat "$file" >> tmp_file
mv -f tmp_file "$file"
done
I removed wc
, cut
, ls
and echo
in the places where they're unnecessary. I changed some of the filenames to make them a little more meaningful. I broke it out onto multiple lines only to make it easier to read.
If you want to get fancy, you could use mktemp
or tempfile
to create a temporary filename instead of using a hard coded one.
Edit
Using GNU split
it's possible to do this:
split_filter () { { head -n 1 file.txt; cat; } > "$FILE"; }; export -f split_filter; tail -n +2 file.txt | split --lines=4 --filter=split_filter - split_
Broken out for readability:
split_filter () { { head -n 1 file.txt; cat; } > "$FILE"; }
export -f split_filter
tail -n +2 file.txt | split --lines=4 --filter=split_filter - split_
When --filter
is specified, split
runs the command (a function in this case, which must be exported) for each output file and sets the variable FILE
, in the command's environment, to the filename.
A filter script or function could do any manipulation it wanted to the output contents or even the filename. An example of the latter might be to output to a fixed filename in a variable directory: > "$FILE/data.dat"
for example.
Solution 2 - Linux
This one-liner will split the big csv into pieces of 999 records, preserving the header row at the top of each one (so 999 records + 1 header = 1000 rows)
cat bigFile.csv | parallel --header : --pipe -N999 'cat >file_{#}.csv'
Based on Ole Tange's answer. (re Ole's answer: You can't use line count with pipepart)
See comments for some tips on installing parallel
Solution 3 - Linux
You could use the new --filter functionality in GNU coreutils split >= 8.13 (2011):
tail -n +2 FILE.in | split -l 50 - --filter='sh -c "{ head -n1 FILE.in; cat; } > $FILE"'
Solution 4 - Linux
You can use [mg]awk:
awk 'NR==1{
header=$0;
count=1;
print header > "x_" count;
next
}
!( (NR-1) % 100){
count++;
print header > "x_" count;
}
{
print $0 > "x_" count
}' file
100 is the number of lines of each slice. It doesn't require temp files and can be put on a single line.
Solution 5 - Linux
I'm a novice when it comes to Bash-fu, but I was able to concoct this two-command monstrosity. I'm sure there are more elegant solutions.
$> tail -n +2 file.txt | split -l 4
$> for file in `ls xa*`; do echo "`head -1 file.txt`" > tmp; cat $file >> tmp; mv -f tmp $file; done
This is assuming your input file is file.txt
, you're not using the prefix
argument to split
, and you're working in a directory that doesn't have any other files that start with split
's default xa*
output format. Also, replace the '4' with your desired split line size.
Solution 6 - Linux
Use GNU Parallel:
parallel -a bigfile.csv --header : --pipepart 'cat > {#}'
If you need to run a command on each of the parts, then GNU Parallel can help do that, too:
parallel -a bigfile.csv --header : --pipepart my_program_reading_from_stdin
parallel -a bigfile.csv --header : --pipepart --fifo my_program_reading_from_fifo {}
parallel -a bigfile.csv --header : --pipepart --cat my_program_reading_from_a_file {}
If you want to split into 2 parts per CPU core (e.g. 24 cores = 48 equal sized parts):
parallel --block -2 -a bigfile.csv --header : --pipepart my_program_reading_from_stdin
If you want to split into 10 MB blocks:
parallel --block 10M -a bigfile.csv --header : --pipepart my_program_reading_from_stdin
Solution 7 - Linux
This is a more robust version of Denis Williamson's script. The script creates a lot of temporary files, and it would be a shame if they were left lying around if the run was incomplete. So, let's add signal trapping (see http://tldp.org/LDP/Bash-Beginners-Guide/html/sect_12_02.html and then http://tldp.org/LDP/abs/html/debugging.html) and remove our temporary files; this is a best practice anyways.
trap 'rm split_* tmp_file ; exit 13' SIGINT SIGTERM SIGQUIT
tail -n +2 file.txt | split -l 4 - split_
for file in split_*
do
head -n 1 file.txt > tmp_file
cat $file >> tmp_file
mv -f tmp_file $file
done
Replace '13' with whatever return code you want. Oh, and you should probably be using mktemp anyways (as some have already suggested), so go ahead and remove 'tmp_file" from the rm in the trap line. See the signal man page for more signals to catch.
Solution 8 - Linux
I liked the awk version of marco, adopted from this a simplified one-liner where you can easily specify the split fraction as granular as you want:
awk 'NR==1{print $0 > FILENAME ".split1"; print $0 > FILENAME ".split2";} NR>1{if (NR % 10 > 5) print $0 >> FILENAME ".split1"; else print $0 >> FILENAME ".split2"}' file
Solution 9 - Linux
I really liked Rob and Dennis' versions, so much so that I wanted to improve them.
Here's my version:
in_file=$1
awk '{if (NR!=1) {print}}' $in_file | split -d -a 5 -l 100000 - $in_file"_" # Get all lines except the first, split into 100,000 line chunks
for file in $in_file"_"*
do
tmp_file=$(mktemp $in_file.XXXXXX) # Create a safer temp file
head -n 1 $in_file | cat - $file > $tmp_file # Get header from main file, cat that header with split file contents to temp file
mv -f $tmp_file $file # Overwrite non-header containing file with header-containing file
done
Differences:
- in_file is the file argument you want to split maintaining headers
- Use
awk
instead oftail
due toawk
having better performance - split into 100,000 line files instead of 4
- Split file name will be input file name appended with an underscore and numbers (up to 99999 - from the "-d -a 5" split argument)
- Use mktemp to safely handle temporary files
- Use single
head | cat
line instead of two lines
Solution 10 - Linux
Below is a 4 liner that can be used to split a bigfile.csv into multiple smaller files, and preserve the csv header. Uses only built-in Bash commands (head, split, find, grep, xargs, and sed) which should work on most *nix systems. Should also work on Windows if you install mingw-64 / git-bash.
csvheader=
head -1 bigfile.csv
split -d -l10000 bigfile.csv smallfile_ find .|grep smallfile_ | xargs sed -i "1s/^/$csvheader\n/" sed -i '1d' smallfile_00
Line by line explanation:
- Capture the header to a variable named csvheader
- Split the bigfile.csv into a number of smaller files with prefix smallfile_
- Find all smallfiles and insert the csvheader into the FIRST line using xargs and sed -i. Note that you need to use sed within "double quotes" in order to use variables.
- The first file named smallfile_00 will now have redundant headers on lines 1 and 2 (from the original data as well as from the sed header insert in step 3). We can remove the redundant header with sed -i '1d' command.
Solution 11 - Linux
Inspired by @Arkady's comment on a one-liner.
- MYFILE variable simply to reduce boilerplate
split
doesn't show file name, but the--additional-suffix
option allows us to easily control what to expect- removal of intermediate files via
rm $part
(assumes no files with same suffix)
MYFILE=mycsv.csv && for part in $(split -n4 --additional-suffix=foo $MYFILE; ls *foo); do cat <(head -n1 $MYFILE) $part > $MYFILE.$part; rm $part; done
Evidence:
-rw-rw-r-- 1 ec2-user ec2-user 32040108 Jun 1 23:18 mycsv.csv.xaafoo
-rw-rw-r-- 1 ec2-user ec2-user 32040108 Jun 1 23:18 mycsv.csv.xabfoo
-rw-rw-r-- 1 ec2-user ec2-user 32040108 Jun 1 23:18 mycsv.csv.xacfoo
-rw-rw-r-- 1 ec2-user ec2-user 32040110 Jun 1 23:18 mycsv.csv.xadfoo
and of course head -2 *foo
to see the header is added.
Solution 12 - Linux
A simple but maybe not as elegant way: Cut off the header beforehand, split the file, and then rejoin the header on each file with cat, or with whatever file is reading it in. So something like:
- head -n1 file.txt > header.txt
- split -l file.txt
- cat header.txt f1.txt