bash's parameter expansion

[bash's parameter expansion]

　#: find first from left, remove-left

　##: find last from left, remove left

　%: find first from right, remove right

　%%: find last from right, remove right

　example 1:

1 parameter     result

2 -----------   ------------------------------

3 ${NAME}       polish.ostrich.racing.champion

4 ${NAME#*.}           ostrich.racing.champion

5 ${NAME##*.}                         champion

6 ${NAME%%.*}   polish

7 ${NAME%.*}    polish.ostrich.racing

　example 2:

1 parameter     result

2 -----------   --------------------------------------------------------

3 ${FILE}       /usr/share/java-1.4.2-sun/demo/applets/Clock/Clock.class

4 ${FILE#*/}     usr/share/java-1.4.2-sun/demo/applets/Clock/Clock.class

5 ${FILE##*/}                                                Clock.class

6 ${FILE%%/*}

7 ${FILE%/*}    /usr/share/java-1.4.2-sun/demo/applets/Clock

 string slice: 

${string:2:1}   # The third character of string (0, 1, 2 = third)

${string:1}     # The string starting from the second character

                # Note: this is equivalent to ${string#?}

${string%?}     # The string with its last character removed.

${string: -1}   # The last character of string

${string:(-1)}  # The last character of string, alternate syntax

                # Note: string:-1 means something entirely different; see below.



${file%.mp3}    # The filename without the .mp3 extension

                # Very useful in loops of the form: for file in *.mp3; do ...

${file%.*}      # The filename without its last extension

${file%%.*}     # The filename without all of its extensions

${file##*.}     # The extension only, assuming there is one. If not, will expand to ${file}

 toupper (^) and tolower (,):

1 # string='hello, World!'

2 parameter     result

3 -----------   --------------------------------------------------------

4 ${string^}    Hello, World! # First character to uppercase

5 ${string^^}   HELLO, WORLD! # All characters to uppercase

6 ${string,}    hello, World! # First character to lowercase

7 ${string,,}   hello, world! # All characters to lowercase

assignment:

1 ${var-word}             # if var is defined, use var; otherwise, "word"

2 ${var+word}             # if var is defined, use "word"; otherwise, nothing

3 ${var=word}             # if var is defined, use var; otherwise, use "word" AND...

4                         #   also assign "word" to var

5 ${var?error}            # if var is defined, use var; otherwise print "error" and exit

参考: http://bash.cumulonim.biz/BashFAQ(2f)073.html