IFS and $* variables in the shell

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Self-documenting content. The shell script that encountered the relevant content in the project. Record in this place

string1="111 222 333 4444"echo  $STRING 1echo"$ STRING1"

The output of both pieces of code is

111 222 333 4444

The second piece of code

string2="111 222  333   444"echo  $STRING 2echo"  $STRING 2"

Output Result:

111 222 333 444 111 222  333   444

The reason for this is the IFS variable: IFS is a shell-defined variable, the default value is <space><tab><newline>3, the role of IFS is to put a string of such a character (and its same character, For example, the above <space>,<tab> <newline> escape is a delimiter, for example the above string is actually

111<space>222<space>333<space><space><space>444 

Because IFS also has a <spce> in it, so in his eyes <space> is the delimiter, it is adjacent to the continuous division to meet and together. And the strings wrapped in double quotes are actually shielding the IFS, and when I make the following changes, the output is exactly the same.

ifs='&'STRING2="111 222  333   444" Echo $STRING 2 Echo " $STRING 2 "

Another variable is $*, which refers to a string collection of script entry parameters. Examples are as follows:

A command was entered at the terminal, as follows:

111 222 333

The output of its echo $* is

111 222 333

Next look at the following code

ifs='&'STRING2="111&222&&333&&& 444"echo  $STRING 2echo"$STRING 2"

Its output is

111  222  333   444 111&222&&333&&&444

Because ifs= ' & ', the & in the string is completely delimited, so the first output is 111 222 333 444, followed by a set of code. (Note also that not all separators are merged.) Where spaces are merged, for example)

Now run at Terminal

111 222  333   444 IFS='&'echo $*echo'$*' 

Its output is

111 222 333 444 111&222&333&444

Because $* equals 111ifs222ifs333ifs444, also equals 111&222&333&444, because Echo $* when,& represents a delimiter, it is converted to a space, and the second line because of the "" Effect makes & No conversions Made

IFS and $* variables in the shell