CLI tip 21: inplace file editing with GNU awk

You can use the -i option with GNU awk to load libraries. The inplace library comes by default with the GNU awk installation. Thus, you can use -i inplace to modify the original input itself. Make sure to test that the code is working as intended before using this option.

$ cat table.txt
brown bread mat cake 42
blue cake mug shirt -7
yellow banana window shoes 3.14

# retain only the first and third fields
$ awk -i inplace '{print $1, $3}' table.txt
$ cat table.txt
brown mat
blue mug
yellow window

You can provide a backup extension by setting the inplace::suffix special variable. For example, if the input file is ip.txt and inplace::suffix='.orig' is used, the backup file will be named as ip.txt.orig.

$ cat marks.txt
  Name    Physics  Maths
 Moe  76  82
Raj  56  64

$ awk -i inplace -v inplace::suffix='.bkp' -v OFS=, '{$1=$1} 1' marks.txt
$ cat marks.txt
Name,Physics,Maths
Moe,76,82
Raj,56,64

# original file is preserved in 'marks.txt.bkp'
$ cat marks.txt.bkp
  Name    Physics  Maths
 Moe  76  82
Raj  56  64

Earlier versions of GNU awk used INPLACE_SUFFIX variable instead of inplace::suffix. Also, you can use inplace::enable variable to dynamically control whether files should be inplaced or not. See gawk manual: Enabling In-Place File Editing for more details.

See this unix.stackexchange thread for details about security implications of using the -i option and workarounds.

Video demo:

See my CLI text processing with GNU awk ebook if you are interested in learning about the GNU awk command in more detail.