在Mac OS下，一些jpg的文件出现了无法在iPhone模拟器识别的问题，估计就是jpg应该是大写，图片全部更改后缀，这手动更改麻烦啊，于是就shell了以下，又man了一会终于知道了！
for i in *.jpg; do
mv $i $(echo $i | cut -d . -f 1).JPG ;
done
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作用就是将所有小写的jpg文件更改为大写。这需要将文件名和后缀分割开，所以使用cut，再对返回值加上后缀JPG，完成。
再附上cut的man手册，mac就是从BSD改出来的。这BSD的man很老，还是喜欢linux的shell，命令新，选项全。。
UT(1) BSD General Commands Manual CUT(1)
NAME
cut -- select portions of each line of a file
SYNOPSIS
cut -b list [-n] [file ...]
cut -c list [file ...]
cut -f list [-d delim] [-s] [file ...]
DESCRIPTION
The cut utility selects portions of each line (as specified by list) from
each file and writes them to the standard output. If no file arguments
are specified, or a file argument is a single dash (`-'), cut reads from
the standard input. The items specified by list can be in terms of col-
umn position or in terms of fields delimited by a special character.
Column numbering starts from 1.
The list option argument is a comma or whitespace separated set of
increasing numbers and/or number ranges. Number ranges consist of a num-
ber, a dash (`-'), and a second number and select the fields or columns
from the first number to the second, inclusive. Numbers or number ranges
may be preceded by a dash, which selects all fields or columns from 1 to
the first number. Numbers or number ranges may be followed by a dash,
which selects all fields or columns from the last number to the end of
the line. Numbers and number ranges may be repeated, overlapping, and in
any order. It is not an error to select fields or columns not present in
the input line.
The options are as follows:
-b list
The list specifies byte positions.
-c list
The list specifies character positions.
-d delim
Use delim as the field delimiter character instead of the tab
character.
-f list
The list specifies fields, separated in the input by the field
delimiter character (see the -d option.) Output fields are sepa-
rated by a single occurrence of the field delimiter character.
-n Do not split multi-byte characters. Characters will only be out-
put if at least one byte is selected, and, after a prefix of zero
or more unselected bytes, the rest of the bytes that form the
character are selected.
-s Suppress lines with no field delimiter characters. Unless speci-
fied, lines with no delimiters are passed through unmodified.
ENVIRONMENT
The LANG, LC_ALL and LC_CTYPE environment variables affect the execution
of the cut utility. Their effect is described in environ(7).
EXIT STATUS
The cut utility exits 0 on success, and >0 if an error occurs.
EXAMPLES
Extract users' login names and shells from the system passwd(5) file as
``name:shell'' pairs:
cut -d : -f 1,7 /etc/passwd
Show the names and login times of the currently logged in users:
who | cut -c 1-16,26-38
SEE ALSO
colrm(1), paste(1)
STANDARDS
The cut utility conforms to IEEE Std 1003.2-1992 (``POSIX.2'
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