Convert camelCase to Underscores Using sed

This short post deals with converting strings of the form camelCase or CamelCase into camel_case, and vice versa. These are three different popular naming conventions for variable/function/class names.

Convert CamelCase or camelCase to camel_case:

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sed -e 's/\([A-Z]\)/_\l\1/g' -e 's/^_\([a-z]\)/\1/g' file.txt

Convert camel_case to camelCase

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sed -e 's/_\([a-z]\)/\u\1/g' file.txt

Convert camel_case to CamelCase:

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sed -e 's/_\([a-z]\)/\u\1/g' -e 's/^\([a-z]\)/\u\1/g' file.txt

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Saturday, May 30th, 2009 Bash

5 Comments to Convert camelCase to Underscores Using sed

  • Michael says:
    June 30, 2009 at 12:33 pm

    Thanks for sharing this Amir.

    Would it be possible to carry out the following in one script or command?

    camelCase => camel_case
    camelCaseLong => camel_case_long
    camelCaseXYZ => camel_case_xyz

    CamelCase => Camel_Case
    CamelCaseLong => Camel_Case_Long
    CamelCaseXYZ => Camel_Case_XYZ

    I’m open to all suggestions.

    Many thanks,

    Michael

  • Amir Watad says:
    July 3, 2009 at 11:11 am

    This does half of the job:

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    sed -e 's/\([a-z]\)\([A-Z]\)/\1_\2/g' -e 's/^_\([a-zA-Z]\)/\1/g' file.txt

    Will try to find a complete solution as soon as I have time.

  • Michael says:
    July 5, 2009 at 1:18 pm

    I look forward to a full solution.

    Thanks again Amir.

  • Manish Sinha says:
    September 2, 2009 at 8:50 pm

    AFAIK

    TcpListener– this is PascalCase
    tcpListener — this is camelCase

  • Oran says:
    October 8, 2009 at 6:18 am

    Another solution to convert camel_case to CamelCase:
    sed -e ‘s/\(^\|_\)\(.\)/\U\2/g’

    • Leave a Reply

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