16.7.4 Enabling In-Place File Editing

The inplace extension emulates GNU sed’s -i option, which performs “in-place” editing of each input file. It uses the bundled inplace.awk include file to invoke the extension properly:

# inplace --- load and invoke the inplace extension.

@load "inplace"

# Please set INPLACE_SUFFIX to make a backup copy.  For example, you may
# want to set INPLACE_SUFFIX to .bak on the command line or in a BEGIN rule.

# N.B. We call inplace_end() in the BEGINFILE and END rules so that any
# actions in an ENDFILE rule will be redirected as expected.

BEGINFILE {
    if (_inplace_filename != "")
        inplace_end(_inplace_filename, INPLACE_SUFFIX)
    inplace_begin(_inplace_filename = FILENAME, INPLACE_SUFFIX)
}

END {
    inplace_end(FILENAME, INPLACE_SUFFIX)
}

For each regular file that is processed, the extension redirects standard output to a temporary file configured to have the same owner and permissions as the original. After the file has been processed, the extension restores standard output to its original destination. If INPLACE_SUFFIX is not an empty string, the original file is linked to a backup file name created by appending that suffix. Finally, the temporary file is renamed to the original file name.

The _inplace_filename variable serves to keep track of the current filename so as to not invoke inplace_end() before processing the first file.

If any error occurs, the extension issues a fatal error to terminate processing immediately without damaging the original file.

Here are some simple examples:

$ gawk -i inplace '{ gsub(/foo/, "bar") }; { print }' file1 file2 file3

To keep a backup copy of the original files, try this:

$ gawk -i inplace -v INPLACE_SUFFIX=.bak '{ gsub(/foo/, "bar") }
> { print }' file1 file2 file3