如何统计一个文件中各个字母出现的次数？

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代码:

[color=red]$ cat count_char.sh[/color]
#!/bin/bash

ALL_CHARS=abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ

for ((i = 0; i < ${#ALL_CHARS}; ++i)); do
    ch=${ALL_CHARS:$i:1}
    eval "count_$ch=0"
done

echo "Counting, wait a while ..."

while read -n 1 ch; do
    if expr index $ALL_CHARS "$ch" >& /dev/null; then
        eval "((count_$ch++))"
    fi
done

for ((i = 0; i < ${#ALL_CHARS}; ++i)); do
    ch=${ALL_CHARS:$i:1}
    eval "echo $ch: \$count_$ch"
done

[color=red]$ ./count_char.sh < /your/file[/color]