Patching Text Files
Simple tricks for updating text files with perl
Notes
Take theses three perl command options:
-ienables editing files in place, with the option to back up the original file first.-passume “while (<>) { print; }” loop around the program, so it works like sed-eexecutes the program given on the command line
Together these allow simple one-liners for modifying text files with arbitrary complexity: from simple substitutions to conditional and sophisticated modifications.
The examples.sh script has two examples to demonstrate the principle.
NB: on posix systems, use single quotes for -e programs to avoid shell command substitution.
Example
Running the example:
$ ./examples.sh
# Installing example.txt from template..
# Original file (example.txt):
line=1
line=2
my_key=old.host.com
line=3
line=4
# Example 1: General substitution (no file backup)
# changes all lines with 'line=*' to 'row=*'
# .. diff after change:
1,2c1,2
< row=1
< row=2
---
> line=1
> line=2
4,5c4,5
< row=3
< row=4
---
> line=3
> line=4
# Example 2: Dependent substitution (with backup)
# changes the right-hand-side of the line matching 'my_key='
# .. diff after change:
3c3
< my_key=new.service.io
---
> my_key=old.host.com
# Final example.txt after all these changes:
row=1
row=2
my_key=new.service.io
row=3
row=4
Operating on Multiple Files
Combine with find:
find . -name "example.txt" -exec perl -i -pe '
s/my_key/$ARGV[0]/;
if ( eof ) {
print;
close ARGV;
exit;
}
' {} "my_new_key" \;
Note: to exclude paths from the find, say to exclude the lib folder, add a path with the prune option:
find . -path ./lib -prune -o -name "example.txt" ..
This reads as: find from here, prune ./lib paths or (-o) match name example.txt