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I read a command from https://unix.stackexchange.com/a/175845/674

Why can

$ bash -c 'for f do echo "$f";done' bash a b c

a

b

c

output the same as

$ bash -c 'for f in "$@"; do echo "$f";done' bash a b c

a

b

c

?

Why does a for-loop not require explicitly specifying

• the set of values of the loop variable, as in "$@" and




• ; ?

Thanks.

From the bash man page:

for name [ [ in [ word ... ] ] ; ] do list ; done

The list of words
following in is expanded, generating a list of items. The variable
name is set to each element of this list in turn, and list is executed
each time. If the in word is omitted, the for command executes list
once for each positional parameter that is set (see PARAMETERS below). ...

Then from the parameters section:

A positional parameter is a parameter denoted by one or more digits,
other than the single digit 0. Positional parameters are assigned from
the shell's arguments when it is invoked, and may be reassigned using
the set builtin command. ...

In summary, the in keyword and following semicolon are optional. If you omit the in keyword, the parameters for the for loop are taken from the arguments passed to the shell. Therefore, the two code samples you provide are equivalent.