Why is this script working? [BASH]

[neur0]

I was reading a book on shell scripting and found this example:



#!/bin/sh
pattern="$1"
shift
echo "Matching against '$pattern':"
for string
do
case $string in
$pattern) echo "$string: Match." ;;
*) echo "$string: No match." ;;
esac
done


This little script works as expected and accepts multiple arguments, but how does it substitute the values of the "STRING" variable when "shift" is not inside the loop?
I am new to shell scripting but I just hate it when I find something that works and I don't know why it works. No troubleshooting can give me an answer to this one so I thought I try the forums. Also, using "for" without some kind of a list/array is poorly documented on the internet.

[geirha]

When you omit the in words part, it assumes in "$@". Run help for in an interactive bash shell to see the syntax.

Out of curiosity, which book is it?

[gmargo]

from the dash(1) man page:


The syntax of the for command is

for variable [ in [ word ... ] ]
do list
done

The words following in are expanded, and then the list is executed repeatedly with the variable set to each
word in turn. Omitting in word ... is equivalent to in "$@".
So your 'for string' is the same as 'for string in "$@"', which expands to all the remaining command line arguments.

[Bachstelze]

From the zsh manual, I expect Bash works the same way:


for name ... [ in word ... ] term do list done
where term is at least one newline or ;. Expand the list of words, and set the parameter name
to each of them in turn, executing list each time. If the in word is omitted, use the posi-
tional parameters instead of the words.

[neur0]

Ah,
Thanks for those answers, I understand it now.

It from the "Beginning Portable Shell Scripting: From Novice to Professional" btw

[geirha]

Ah,
Thanks for those answers, I understand it now.

It from the "Beginning Portable Shell Scripting: From Novice to Professional" btw

Aha, in that case this thread's title is misleading. Based on the title on that book, it most likely teaches you to write sh scripts, not bash scripts.