What's the difference between $@ and $* in UNIX?
Please see the bash man page under Special Parameters.
Special Parameters The shell treats several parameters specially. These parameters may only be referenced; assignment to them is not allowed. * Expands to the positional parameters, starting from one. When the expansion occurs within double quotes, it expands to a sin‐ gle word with the value of each parameter separated by the first character of the IFS special variable. That is, "$*" is equiva‐ lent to "$1c$2c...", where c is the first character of the value of the IFS variable. If IFS is unset, the parameters are sepa‐ rated by spaces. If IFS is null, the parameters are joined without intervening separators. @ Expands to the positional parameters, starting from one. When the expansion occurs within double quotes, each parameter expands to a separate word. That is, "$@" is equivalent to "$1" "$2" ... If the double-quoted expansion occurs within a word, the expansion of the first parameter is joined with the begin‐ ning part of the original word, and the expansion of the last parameter is joined with the last part of the original word. When there are no positional parameters, "$@" and $@ expand to nothing (i.e., they are removed).
One difference is in how they handle the IFS variable on output.
#!/bin/shecho "unquoted asterisk " $*echo "quoted asterisk $*"echo "unquoted at " $@echo "quoted at $@"IFS="X"echo "IFS is now $IFS"echo "unquoted asterisk " $*echo "quoted asterisk $*"echo "unquoted at " $@echo "quoted at $@"
If you run this like this: ./demo abc def ghi
, you get this output:
unquoted asterisk abc def ghiquoted asterisk abc def ghiunquoted at abc def ghiquoted at abc def ghiIFS is now Xunquoted asterisk abc def ghiquoted asterisk abcXdefXghiunquoted at abc def ghiquoted at abc def ghi
Notice that (only) the "quoted asterisk" line shows an X between each "word" after IFS
is changed to "X". If the value of IFS
contains multiple characters, only the first character is used for this purpose.
This feature can also be used for other arrays:
$ array=(123 456 789)$ saveIFS=$IFS; IFS="|"$ echo "${array[*]}"123|456|789$ IFS=$saveIFS