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Destroyed SC2012 (markdown)

metro44060
2020-03-21 04:44:56 -04:00
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SC2012.md

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## Use `find` instead of `ls` to better handle non-alphanumeric filenames.
### Problematic code:
```sh
ls -l | grep " $USER " | grep '\.txt$'
```
```sh
NUMGZ="$(ls -l *.gz | wc -l)"
```
### Correct code:
```sh
find . -maxdepth 1 -name '*.txt' -user "$USER" # Using the names of the files
```
```sh
gz_files=(*.gz)
numgz=${#gz_files[@]} # Sometimes, you just need a count
````
### Rationale:
`ls` is only intended for human consumption: it has a loose, non-standard format and may "clean up" filenames to make output easier to read.
Here's an example:
```sh
$ ls -l
total 0
-rw-r----- 1 me me 0 Feb 5 20:11 foo?bar
-rw-r----- 1 me me 0 Feb 5 2011 foo?bar
-rw-r----- 1 me me 0 Feb 5 20:11 foo?bar
```
It shows three seemingly identical filenames, and did you spot the time format change? How it formats and what it redacts can differ between locale settings, `ls` version, and whether output is a tty.
### Tips for replacing `ls` with `find`:
#### Just the filenames, ma'am
`ls` can usually be replaced by `find` if it's just the filenames, or a count of them, that you're after. Note that if you are using `ls` to get at the contents of a directory, a straight substitution of `find` may not yield the same results as `ls`. Here is an example:
```
$ ls -c1 .snapshot
rnapdev1-svm_4_05am_6every4hours.2019-04-01_1605
rnapdev1-svm_4_05am_6every4hours.2019-04-01_2005
rnapdev1-svm_4_05am_6every4hours.2019-04-02_0005
rnapdev1-svm_4_05am_6every4hours.2019-04-02_0405
rnapdev1-svm_4_05am_6every4hours.2019-04-02_0805
rnapdev1-svm_4_05am_6every4hours.2019-04-02_1205
snapmirror.1501b4aa-3f82-11e8-9c31-00a098cef13d_2147868328.2019-04-01_190000
```
versus
```
$ find .snapshot -maxdepth 1
.snapshot
.snapshot/rnapdev1-svm_4_05am_6every4hours.2019-04-02_0005
.snapshot/rnapdev1-svm_4_05am_6every4hours.2019-04-02_0405
.snapshot/rnapdev1-svm_4_05am_6every4hours.2019-04-02_0805
.snapshot/rnapdev1-svm_4_05am_6every4hours.2019-04-01_1605
.snapshot/rnapdev1-svm_4_05am_6every4hours.2019-04-01_2005
.snapshot/rnapdev1-svm_4_05am_6every4hours.2019-04-02_1205
.snapshot/snapmirror.1501b4aa-3f82-11e8-9c31-00a098cef13d_2147868328.2019-04-01_190000
```
You can see two differences here. The first is that the `find` output has the full paths to the found files, relative to the current working directory from which `find` was run whereas `ls` only has the filenames. You may have to adjust your code to not add the directory to the filenames as you process them when moving from `ls` to `find`, or (with GNU find) use `-printf '%P\n'` to print just the filename.
The second difference in the two outputs is that the `find` command includes the searched directory as an entry. This can be eliminated by also using `-mindepth 1` to skip printing the root path, or using a negative name option for the searched directory:
```
$ find .snapshot -maxdepth 1 ! -name .snapshot
.snapshot/rnapdev1-svm_4_05am_6every4hours.2019-04-02_0005
.snapshot/rnapdev1-svm_4_05am_6every4hours.2019-04-02_0405
.snapshot/rnapdev1-svm_4_05am_6every4hours.2019-04-02_0805
.snapshot/rnapdev1-svm_4_05am_6every4hours.2019-04-01_1605
.snapshot/rnapdev1-svm_4_05am_6every4hours.2019-04-01_2005
.snapshot/rnapdev1-svm_4_05am_6every4hours.2019-04-02_1205
.snapshot/snapmirror.1501b4aa-3f82-11e8-9c31-00a098cef13d_2147868328.2019-04-01_190000
```
**Note:** If the directory argument to `find` is a fully expressed path (`/home/somedir/.snapshot`), then you should use `basename` on the `-name` filter:
```
$ theDir="$HOME/.snapshot"
$ find "$theDir" -maxdepth 1 ! -name "$(basename $theDir)"
/home/matt/.snapshot/rnapdev1-svm_4_05am_6every4hours.2019-04-02_0005
/home/matt/.snapshot/rnapdev1-svm_4_05am_6every4hours.2019-04-02_0405
/home/matt/.snapshot/rnapdev1-svm_4_05am_6every4hours.2019-04-02_0805
/home/matt/.snapshot/rnapdev1-svm_4_05am_6every4hours.2019-04-01_1605
/home/matt/.snapshot/rnapdev1-svm_4_05am_6every4hours.2019-04-01_2005
/home/matt/.snapshot/rnapdev1-svm_4_05am_6every4hours.2019-04-02_1205
/home/matt/.snapshot/snapmirror.1501b4aa-3f82-11e8-9c31-00a098cef13d_2147868328.2019-04-01_190000
```
#### All the other info
If trying to parse out any other fields, first see whether `stat` (GNU, OS X, FreeBSD) or `find -printf` (GNU) can give you the data you want directly.
### Exceptions:
If the information is intended for the user and not for processing (`ls -l ~/dir | nl; echo "Ok to delete these files?"`) you can ignore this error with a [[directive]].