Bash Snippet: Trim Function

Occasionally I find myself wanting to removing leading and/or trailing occurrences of a character or string from a larger string in bash. A couple common uses are removing quotes, or stripping an unknown number of spaces leading into the data of interest. This can be done pretty easily with other methods such as awk or sed, but with the disadvantage of requiring external commands. This a pure bash implementation using only shell built-ins. It might be better to rewrite this with $BASH_REMATCH, but this is what I currently have.

#!/bin/bash



trim () {

    str="$1"

    match="$2"

    # trim spaces by default

    if [ -z "$match" ]; then

        match=" "

    fi

    # trim leading

    while [ "${str:0:${#match}}" == "$match" ];

    do

        str="${str:${#match}:${#str}}"

    done

    # trim tailing

    while [ "${str:$((${#str}-${#match}))}" == "$match" ];

    do

        str="${str:0:$((${#str} - ${#match}))}" 

    done

    echo "$str"

}



#Remove leading and trailing spaces

example="    Hello     "

echo "`trim  "$example" " "`"



#The second parameter is optional when removing spaces

example="    Hello     "

echo "`trim  "$example"`"





#Remove leading and trailing occurences of "word"

example="wordHelloword"

echo "`trim  "$example" "word"`"