string.functions.sh

《linux应用开发技术详解》的配套代码

#!/bin/bash

# function strcat
# Usage: strcat s1 s2
function strcat ()
{
    local s1_val s2_val

    s1_val=${!1}                        # indirect variable expansion
    s2_val=${!2}
    eval "$1"=\'"${s1_val}${s2_val}"\'
    # ==> eval $1='${s1_val}${s2_val}' avoids problems,
    # ==> if one of the variables contains a single quote.
}

#:function strncat
# Usage: strncat s1 s2 $n
function strncat ()
{
    local -i n="$3"
    local s1_val s2_val

    s1_val=${!1}                       # ==> indirect variable expansion
    s2_val=${!2}

    if [ ${#s2_val} -gt ${n} ]; then
       s2_val=${s2_val:0:$n}            # ==> substring extraction
    fi

    eval "$1"=\'"${s1_val}${s2_val}"\'
    # ==> eval $1='${s1_val}${s2_val}' avoids problems,
    # ==> if one of the variables contains a single quote.
}

# function strcmp
# Usage: strcmp $s1 $s2
function strcmp ()
{
    [ "$1" = "$2" ] && return 0

    [ "${1}" '<' "${2}" ] > /dev/null && return -1

    return 1
}

# function strncmp
# Usage: strncmp $s1 $s2 $n
function strncmp ()
{
    if [ -z "${3}" -o "${3}" -le "0" ]; then
       return 0
    fi
   
    if [ ${3} -ge ${#1} -a ${3} -ge ${#2} ]; then
       strcmp "$1" "$2"
       return $?
    else
       s1=${1:0:$3}
       s2=${2:0:$3}
       strcmp $s1 $s2
       return $?
    fi
}

# function strlen
# Usage: strlen s
function strlen ()
{
    eval echo "\${#${1}}"
    # ==> Returns the length of the value of the variable
    # ==> whose name is passed as an argument.
}

# function strspn
# Usage: strspn $s1 $s2
function strspn ()
{
    # Unsetting IFS allows whitespace to be handled as normal chars. 
    local IFS=
    local result="${1%%[!${2}]*}"
 
    echo ${#result}
}

# function strcspn
# Usage: strcspn $s1 $s2
function strcspn ()
{
    # Unsetting IFS allows whitspace to be handled as normal chars. 
    local IFS=
    local result="${1%%[${2}]*}"
 
    echo ${#result}
}

# function strstr
# Usage: strstr $s1 $s2
function strstr ()
{
    # if s2 points to a string of zero length, strstr echoes s1
    [ ${#2} -eq 0 ] && { echo "$1" ; return 0; }

    # strstr echoes nothing if s2 does not occur in s1
    case "$1" in
    *$2*) ;;
    *) return 1;;
    esac

    # use the pattern matching code to strip off the match and everything
    # following it
    first=${1/$2*/}

    # then strip off the first unmatched portion of the string
    echo "${1##$first}"
}

# function strtrunc
# Usage: strtrunc $n $s1 {$s2} {$...}
function strtrunc ()
{
    n=$1 ; shift
    for z; do
        echo "${z:0:$n}"
    done
}