I frequently write for-loops in bash with the well-known syntax:
for i in {1..10} [...] Now, I'm trying to write one where the top is defined by a variable:
TOP=10 for i in {1..$TOP} [...] I've tried a variety of parens, curly-brackets, evaluations, etc, and typically get back an error "bad substitution".
How can I write my for-loop so that the limit depends on a variable instead of a hard-coded value?
You can use for loop like this to iterate with a variable $TOP:
for ((i=1; i<=$TOP; i++)) do echo $i # rest of your code done If you have a gnu system, you can use seq to generate various sequences, including this.
for i in $(seq $TOP); do ... done Answer is partly there : see Example 11-12. A C-style for loop.
Here is a summary from there, but be aware the final answer to your question depends on your bash interpreter (/bin/bash --version):
# Standard syntax. for a in 1 2 3 4 5 6 7 8 9 10 # Using "seq" ... for a in `seq 10` # Using brace expansion ... # Bash, version 3+. for a in {1..10} # Using C-like syntax. LIMIT=10 for ((a=1; a <= LIMIT ; a++)) # Double parentheses, and "LIMIT" with no "$". # another example lines=$(cat $file_name | wc -l) for i in `seq 1 "$lines"` # An another more advanced example: looping up to the last element count of an array : for element in $(seq 1 ${#my_array[@]}) 