Help required to write a one liner to gunzip (and retain gzipped files) for multiple files.

Question

[lakhujanivijay]

Hi,

I am trying to learn writing one liners using shell/awk. To begin with I want to perform the following operation using a one liner.

Scenario: A directory containing multiple fastq files with the extension .fq.gz.

Objective To automate gunzipping all the files and retain the gzipped files i.e. my directory will have *.fq.gz as well as *.fq files.

What I tried so far

I broke the problem into smaller pieces like this:

1. find the files with extension *.fq.gz
2. loop over the files
3. pass files one by one to gunzip command
4. use the option -cto retain the *.fq.gz files
5. the output files should have extension *.fq, so I split the file name by a "." to have 3 parts from the original file name i.e.

original file

test.fq.gz

after splitting

test [part 1]
fq [part 2]
gz [part3 ]

then take part 1 and concatenate ".fq" . Finally I came up with below one liner:

for i in find -name  "*.fq.gz"; do gunzip -c $i > awk '{split($i,a,"."); print a[1] ".fq"}' ; done

However, it is not working, here is the error:

gunzip: find.gz: No such file or directory
gunzip: {split($i,a,"."); print a[2] ".fq"}.gz: No such file or directory
gunzip: invalid option -- e

PS: I googled a lot without much success. This may be a very easy task but I am learning to automate using one liners.

Answer 1

[dyollluap]

Try

for file in *.gz; do gunzip -k $file ; done

You shouldn't need awk for this situation. By default gunzip will name the uncompressed file the same as the .gz , just minus the .gz I think you want the gunzip -k flag to keep the original fq.gz (see gunzip --man)

[shenwei356]

Oh .. I forgot -k. Oh .. I forgot -k.

[lakhujanivijay]

No -k option. Do I have an older version?

for file in *.gz; do gunzip -k $file ; done
gunzip: invalid option -- k
gunzip 1.3.5
(2002-09-30)
usage: gunzip [-cdfhlLnNrtvV19] [-S suffix] [file ...]
 -c --stdout      write on standard output, keep original files unchanged
 -d --decompress  decompress
 -f --force       force overwrite of output file and compress links
 -h --help        give this help
 -l --list        list compressed file contents
 -L --license     display software license
 -n --no-name     do not save or restore the original name and time stamp
 -N --name        save or restore the original name and time stamp
 -q --quiet       suppress all warnings
 -r --recursive   operate recursively on directories
 -S .suf  --suffix .suf     use suffix .suf on compressed files
 -t --test        test compressed file integrity
 -v --verbose     verbose mode
 -V --version     display version number
 -1 --fast        compress faster
 -9 --best        compress better
    --rsyncable   Make rsync-friendly archive
 file...          files to (de)compress. If none given, use standard input.
Report bugs to <[e-mail]>.
gunzip: invalid option -- k
gunzip 1.3.5
(2002-09-30)

[Lars Juhl Jensen]

If you use a gunzip with the -k option, why not simply do gunzip -k *.fq.gz?

Answer 2

[shenwei356]

No find:

 for f in *.fq.gz; do gzip -d -c $f > ${f/\.gz/}; done

With find:

for f in $( find ./ -name "*.fq.gz" ); do gzip -d -c $f > ${f/\.gz/}; done

I tried find -exec but failed.

find ./ -name "*.fq.gz" -exec gzip -d -c {} > ${"{}"/\.gz/} \;
bash: ${"{}"/\.gz/}: bad substitution

Ref: Advanced Bash-Scripting Guide:: Manipulating Strings

[lakhujanivijay]

Can you please explain

 for f in *.fq.gz; do gzip -d -c $f > ${f/\.gz/}; done

1. how is gzip helping here instead of gunzip ?
2. ${f/\.gz/} what is this part ?

[shenwei356]

gzip can compress and decompress.

see the ref. string replacing in shell.

Answer 3

[WouterDeCoster]

Let me throw in a gnu-parallel solution, which isn't so different from the other solutions:

ls *.gz | parallel 'gunzip -k {}'