I am learning awk
and I would like to know if there is an option to write changes to file, similar to sed
where I would use -i
option
@sudo_O has the right answer.
This can't work:
someprocess < file > file
The shell performs the redirections before handing control over to someprocess (redirections). The >
redirection will truncate the file to zero size (redirecting output). Therefore, by the time someprocess gets launched and wants to read from the file, there is no data for it to read.
In GNU Awk 4.1.0 (released 2013) and later, it has the option of "inplace" file editing:
[...] The "inplace" extension, built using the new facility, can be used to simulate the GNU "
sed -i
" feature. [...]
Example usage:
$ gawk -i inplace '{ gsub(/foo/, "bar") }; { print }' file1 file2 file3
To keep the backup:
$ gawk -i inplace -v INPLACE_SUFFIX=.bak '{ gsub(/foo/, "bar") }
> { print }' file1 file2 file3
awk '{awk code}' file | tee file
the tee
command take place and executed after the awk
command is finished due to the |
.
In case you want an awk-only solution without creating a temporary file and usable with version!=(gawk 4.1.0):
awk '{a[b++]=$0} END {for(c=0;c<=b;c++)print a[c]>ARGV[1]}' file
Unless you have GNU awk 4.1.0 or later...
You won't have such an option as sed's -i
option so instead do:
$ awk '{print $0}' file > tmp && mv tmp file
Note: the -i
is not magic, it is also creating a temporary file sed
just handles it for you.
As of GNU awk 4.1.0...
GNU awk
added this functionality in version 4.1.0 (released 10/05/2013). It is not as straight forwards as just giving the -i
option as described in the released notes:
The new -i option (from xgawk) is used for loading awk library files. This differs from -f in that the first non-option argument is treated as a script.
You need to use the bundled inplace.awk
include file to invoke the extension properly like so:
$ cat file
123 abc
456 def
789 hij
$ gawk -i inplace '{print $1}' file
$ cat file
123
456
789
The variable INPLACE_SUFFIX
can be used to specify the extension for a backup file:
$ gawk -i inplace -v INPLACE_SUFFIX=.bak '{print $1}' file
$ cat file
123
456
789
$ cat file.bak
123 abc
456 def
789 hij
I am happy this feature has been added but to me, the implementation isn't very awkish as the power comes from the conciseness of the language and -i inplace
is 8 characters too long i.m.o.
Here is a link to the manual for the official word.
just a little hack that works
echo "$(awk '{awk code}' file)" > file