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Q&A How to extract string from file, run filter, and replace in file with new value?

Both replies, at different points, provided the basis for this working script. Assuming that the 12th line of file has something like:     <p>HERE IS MY TITLE</p> where HERE... begi...

posted 6mo ago by David‭  ·  edited 6mo ago by David‭

Answer
#2: Post edited by user avatar David‭ · 2023-11-30T10:14:41Z (6 months ago)
clarify one point
  • Both replies, at different points, provided the basis for this working script. Assuming that the 12th line of file has something like:
  • ```
  •     <p>HERE IS MY TITLE</p>
  • ```
  • where `HERE...` begins at column 8 (I need to omit the opening `<p>` tag, as noted in the original post), then:
  • ```
  • for filename in chapter-*.xhtml; do
  • new12=$(sed -n '12p' "$filename" | cut -b 8- | se titlecase -n)
  • sed -i -e '12s#^\(.*<p>\).*#'"\1$new12"'#g' "$filename"
  • done
  • ```
  • The two middle lines work this way:
  • **Line 2**:
  • - `sed -n '12p' "$filename"` = print the 12th line of the file
  • - `cut -b 8-` = "[cut](https://www.man7.org/linux/man-pages/man1/cut.1.html)" from the 8th column
  • - `se titlecase -n` = run the `titlecase` script (`-n` prevents it from generating a "newline")
  • - all that assigned to `$new12`.
  • **Line 3**
  • - `sed -i -e '12s#^\(.*<p>\).*#'"\1$new12"'#g'` = replace original line 12, capturing the first part of the line, up to the opening `<p>` in a backreference group, so `\1` in the "replace", combined with the `$new12` value.
  • Produces:
  • ```
  •     <p>Here Is My Title</p>
  • ```
  • in `"$filename"`. Done. :)
  • Both replies, at different points, provided the basis for this working script. Assuming that the 12th line of file has something like:
  • ```
  •     <p>HERE IS MY TITLE</p>
  • ```
  • where `HERE...` begins at column 8 (I need to omit the opening `<p>` tag, as noted in the original post), then:
  • ```
  • for filename in chapter-*.xhtml; do
  • new12=$(sed -n '12p' "$filename" | cut -b 8- | se titlecase -n)
  • sed -i -e '12s#^\(.*<p>\).*#'"\1$new12"'#g' "$filename"
  • done
  • ```
  • The two middle lines work this way:
  • **Line 2**:
  • - `sed -n '12p' "$filename"` = print the 12th line of the file
  • - `cut -b 8-` = "[cut](https://www.man7.org/linux/man-pages/man1/cut.1.html)" from the 8th column, so in this example, passing the string `HERE IS MY TITLE</p>` to the pipe
  • - `se titlecase -n` = run the `titlecase` script (`-n` prevents it from generating a "newline")
  • - all that assigned to `$new12`.
  • **Line 3**
  • - `sed -i -e '12s#^\(.*<p>\).*#'"\1$new12"'#g'` = replace original line 12, capturing the first part of the line, up to the opening `<p>` in a backreference group, so `\1` in the "replace", combined with the `$new12` value.
  • Produces:
  • ```
  •     <p>Here Is My Title</p>
  • ```
  • in `"$filename"`. Done. :)
#1: Initial revision by user avatar David‭ · 2023-11-30T10:13:05Z (6 months ago)
Both replies, at different points, provided the basis for this working script. Assuming that the 12th line of file has something like:

```
    <p>HERE IS MY TITLE</p>
```

where `HERE...` begins at column 8 (I need to omit the opening `<p>` tag, as noted in the original post), then:    

```
for filename in chapter-*.xhtml; do
    new12=$(sed -n '12p' "$filename" | cut -b 8- | se titlecase -n)
    sed -i -e '12s#^\(.*<p>\).*#'"\1$new12"'#g' "$filename"
  done
```

The two middle lines work this way:

**Line 2**:
- `sed -n '12p' "$filename"` = print the 12th line of the file
- `cut -b 8-` = "[cut](https://www.man7.org/linux/man-pages/man1/cut.1.html)" from the 8th column
- `se titlecase -n` = run the `titlecase` script (`-n` prevents it from generating a "newline")
- all that assigned to `$new12`.

**Line 3**  
- `sed -i -e '12s#^\(.*<p>\).*#'"\1$new12"'#g'` = replace original line 12, capturing the first part of the line, up to the opening `<p>` in a backreference group, so `\1` in the "replace", combined with the `$new12` value.

Produces: 

```
    <p>Here Is My Title</p>
```

in `"$filename"`. Done. :)