Gzip – How to Keep Original File

command linefilesgzip

I would like to compress a text file using gzip command line tool while keeping the original file. By default running the following command

gzip file.txt

results in modifying this file and renaming it file.txt.gz. instead of this behavior I would like to have this new compressed file in addition to the existing one file.txt. For now I am using the following command to do that

gzip -c file.txt > file.txt.gz

It works but I am wondering why there is no easier solution to do such a common task ? Maybe I missed the option doing that ?

Best Answer

For GNU gzip 1.6 or above, FreeBSD and derivatives or recent versions of NetBSD, see don_cristi's answer.

With any version, you can use shell redirections as in:

gzip < file > file.gz

When not given any argument, gzip reads its standard input, compresses it and writes the compressed version to its standard output. As a bonus, when using shell redirections, you don't have to worry about files called "--help" or "-" (that latter one still being a problem for gzip -c --).

Another benefit over gzip -c file > file.gz is that if file can't be opened, the command will fail without creating an empty file.gz (or overwriting an existing file.gz) and without running gzip at all.

A significant difference compared to gzip -k though is that there will be no attempt at copying the file's metadata (ownership, permissions, modification time, name of uncompressed file) to file.gz.

Also if file.gz already existed, it will silently override it unless you have turned the noclobber option on in your shell (with set -o noclobber for instance in POSIX shells).

Related Solutions

Use gzip to compress the files in a directory except for already existing .gz files

You can just do:

gzip *

gzip will tell you it skips the files that already have a .gz ending.
If that message gets in the way you can use:

gzip -q *

What you tried did not work, because gzip doesn't read the filenames of the files to compress from stdin, for that to work you would have to use:

ls | grep -v gz | xargs gzip

You will exclude files with the pattern gz anywhere in the file name, not just at the end.¹ You also have to take note that parsing the output of ls is dangerous when you have file names with spaces, newlines, etc., are involved.

A more clean solution, not relying on gzip to skip files with a .gz ending is, that also handles non-compressed files in subdirectories:

find .  -type f ! -name "*.gz" -exec gzip {} \;

¹ _{As izkata commented: using .gz alone to improve this, would not work. You would need to use grep -vF .gz or grep -v '\.gz$'. That still leaves the danger of processing ls' output}

Get compressed size of piped output with gzip

dd to the rescue.

gzip -fc testfile | dd of=testfile.gz
0+1 records in
0+1 records out
42 bytes (42 B) copied, 0.00018711 s, 224 kB/s

or in your ssh example

gzip -fc testfile | dd | ssh serverip "cat > file.gz"
0+1 records in
0+1 records out
42 bytes (42 B) copied, 0.00018711 s, 224 kB/s

And then just parse the output of the commands using awk or somesuch to pluck out the crucial part of the last line.

Best Answer

Related Solutions

Use gzip to compress the files in a directory except for already existing .gz files

Get compressed size of piped output with gzip

Related Question