如何基于外壳脚本中的模式使用grep或sed grep文件名的一部分

Question

I need to get a portion of file name based on a pattern. The file pattern here is not for checking if the file name matches the pattern exactly. The "?"s represent dates, so it can be in the format of YYYYMMDD, or YYYY-MM-DD, and I don't want to get the dates. I guess for now, I will just try to get the letter portion before or after the date portion based on the pattern.

For example, if the file name pattern and the actual file name are:

 *_???????? and file name: ab_cd_20160505_efg.txt

I want to grep the string ab_cd . efg is skipped because it's not part of the pattern.

If the file pattern and the actual file name are:

 ????-??-??_* and file name: 2016-05-05_abc_def-ghi.csv

(contain both dash and undercore), I want to grep the string abc_def-ghi . The .csv is skipped because we don't care about the file extension, that's why we didn't give .csv in the pattern.

So, can someone let me know how to accomplish these using grep or sed or other command in shell script?

Answer 1

a two step approach

$ pattern=$(sed 's/*/([^0-9.]+)/;s/?/[0-9]/g' <<< '*_????????');
$ sed -r "s/$pattern.*/\1/" <<< 'ab_cd_12345678_efg.txt'
ab_cd

$ pattern=$(sed 's/*/([^0-9.]+)/;s/?/[0-9]/g' <<< '????-??-??_*');
$ sed -r "s/$pattern.*/\1/" <<< '1234-56-78_abc_def-ghi.csv'
abc_def-ghi

note the double quotes in the second sed command to let bash expand the pattern.

Answer 2

This does pretty much the same as karakfa's answer , but in Bash:

extract () {
    local pattern="$1"
    local fname="$2"
    pattern="${pattern//\?/[[:digit:]]}"
    pattern="${pattern/\*/([^[:digit:].]+)}"
    [[ $fname =~ $pattern ]]
    echo "${BASH_REMATCH[1]}"
}   

It uses parameter expansion to build a regex pattern by replacing all the ? and * , then matches the filename against that pattern and the printing the first capture group.

For example, the regex generated from *_???????? looks like

([^[:digit:].]+)_[[:digit:]][[:digit:]][[:digit:]][[:digit:]][[:digit:]][[:digit:]][[:digit:]][[:digit:]]

The function can be used like this:

$ extract '*_????????' 'ab_cd_20160505_efg.txt'                                                                     
ab_cd
$ extract '????-??-??_*' '2016-05-05_abc_def-ghi.csv'
abc_def-ghi