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thinksinbinary
Asked: 2016-08-26 17:24:40 +0800 CST

Why isn't simple use of grep not coming up with any results?

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I used find to make a text file containing everything on an external hard drive that has the .mp3 and .wma extension. I wanted to try using grep on the file in order to view the files without the preceding directories (just the lines themselves, it will look less cluttered). However, when i type this:

grep -h "*.mp3" mp3sCIR.txt

nothing pops up. Yes, it's spelled correctly, and the file does actually contain the listing. I tried removing the -h and still nothing. Egrep works but does not suppress filename/path like requested.

grep

1 Answers

  1. Best Answer

    First, you seem to be misunderstanding what the -h flag does.

    -h will suppress the name(s) of the files passed on the command line (i.e. mp3sCIR.txt - although when only a single file is given, the name is not printed by default) - it won't remove anything from the names of the files inside the file.

    Second, you are confusing shell patterns (aka 'globs') and regular expressions - grep uses regex syntax, so to match filenames with the .mp3 extension you'd need1

    grep ".*\.mp3" mp3sCIR.txt

    (which should work the same with or without the -E, since the basic and extended forms are identical).

    To remove the leading pathname components (i.e. what you were attemtping to do with -h) you could use 

    grep -o "[^/]*\.mp3"  mp3sCIR.txt

    to print only the matching portion not including path separators, or with grep in perl compatible (PCRE) mode

    grep -Po ".*/\K.*\.mp3" mp3sCIR.txt


    For future reference, you could have saved the names without leading path components by using find's -printf '%f\n' output format.

    [1] Actually it seems like while BRE treats a bare * at the start of a pattern as literal, ERE (i.e. egrep/grep -E) appears to treat it as a quantifier for an empty expression ("zero or more instances of nothing"); hence grep -E "*.mp3" does match entries with the .mp3 suffix - but not for the reason you'd probably think.

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