The fish documentation gives the following way to run a for loop.
for i in 1 2 3 4 5;
echo $i
end
Let us say I want to run a command 1000 times, How can I do it?
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2 Answers
Same documentation, https://fishshell.com/docs/current/language.html#loops-and-blocks :
for i in (seq 1 5)
echo $i
end
replace seq 1 5 with the numbers you want to get, e.g., seq 14 1000 to get the numbers from 14 to 1000; if you want to start at 1, it's OK to omit the starting point, i.e., write seq 1000.
This, by the way, is like very classical UNIX shells; doesn't feel very modern. (In bash and zsh you can do for i in {1..1000}, which I consider easier and clearer to read, not to mention that it saves actually running an external program seq and buffering its output.)
Another way, which doesn't rely on coreutils (which is kind of a sad thing to rely on if you're not a GNU program nor a POSIX shell), would be using the while loop and purely fish builtin functions:
set counter 0
# -lt: less than
while test $counter -lt 1000;
set counter (math $counter + 1)
echo $counter
end
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See also
repeat 1000 cmdintcshorzsh. I guess, for simple commands, one could easily implement a function that does the same infish.Stéphane Chazelas– Stéphane Chazelas2023-01-16 13:56:09 +00:00Commented Jan 16, 2023 at 13:56 -
In fish that could be
function repeat -a n; while test $n -gt 0; $argv[2..]; set n (math $n - 1); end; endTODO add a guard to validate $nglenn jackman– glenn jackman2023-01-16 15:36:39 +00:00Commented Jan 16, 2023 at 15:36
Turns out there is a program in the gnu-coreutils called seq which prints out a sequence of numbers.
So to run a command n times, the following loop can be used.
for i in (seq n);
echo $i
end
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this works for small n, as the shell needs to generate the sequence from 1...n before going through the for loop. Try the iterative method for less ram usagemdave16– mdave162023-11-06 20:58:19 +00:00Commented Nov 6, 2023 at 20:58
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@mdave16
fishis almost exclusively used for interactive shells, not as automation shell in very resource-constrained machines. You can run this up to524288(tested on fish 3.7.0 on x86_64); that uses less than 150 MB of RAM. If you're processing more than half a million anything in a shell function, I hope you're not doing it with less than half a Gigabyte of RAM. In fact, rule of thumb: whatever you do more than 2000 times, don't do it in your shell, no matter what your shell is; you probably have a problem that benefits from a more fully-fledged language.Marcus Müller– Marcus Müller2025-02-24 12:56:21 +00:00Commented Feb 24 at 12:56