For loop with an argument based range

Question

I want to run certain actions on a group of lexicographically named files (01-09 before 10). I have to use a rather old version of FreeBSD (7.3), so I can\'t use yummies like

Answer 1

Bash supports C-style for loops:

s=1
e=30
for i in ((i=s; i

The syntax you attempted doesn't work because brace expansion happens before parameter expansion, so when the shell tries to expand {$1..$2}, it's still literally {$1..$2}, not {1..30}.

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The answer given by @Kent works because eval goes back to the beginning of the parsing process. I tend to suggest avoiding making habitual use of it, as eval can introduce hard-to-recognize bugs -- if your command were whitelisted to be run by sudo and $1 were, say, '$(rm -rf /; echo 1)', the C-style-for-loop example would safely fail, and the eval example... not so much.

Granted, 95% of the scripts you write may not be accessible to folks executing privilege escalation attacks, but the remaining 5% can really ruin one's day; following good practices 100% of the time avoids being in sloppy habits.

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Thus, if one really wants to pass a range of numbers to a single command, the safe thing is to collect them in an array:

a=( )
for i in ((i=s; i