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up vote 3 down vote favorite

A toy example:

I want to run the following commands sequentially

python generate.py 1
python simulate.py 1
python generate.py 2
python simulate.py 2
...
python generate.py 100
python simulate.py 100

Given the large number of commands, I'd like to use a for loop along the lines

for i in {1..100}; do \
    python generate.py $i; python simulate.py $i; \
done

It's very important for the jobs to run one after the next. Am I doing it correctly?

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1  
I wonder if the use of backslashes is necessary? –  mohammad .k yesterday
    
You don't need the backslashes, although using them is fine (except that it will look like you are joining them in one long line to the lexer). –  Arthur2e5 yesterday
9  
Better to join the commands with && to prevent the second running if the first fails. –  User112638726 yesterday

2 Answers 2

up vote 8 down vote

Yes, you are doing this correctly. The loop you've written will execute the commands in the exact order you listed them out long-hand, though it is important to note that an error in one command will not cause the loop to terminate, it will continue with the next command, effectively ignoring the error.

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Thanks, John! If I may, I have another question. Previously, I had for i in {1..100}; do python generate.py $i python simulate.py $i done but it didn't work, difference being in the semi-colons. Sorry, I'm new to this so I couldn't create new lines correctly in the comment. Can you explain why? –  Godwin Yung yesterday
    
The problem was that you needed a "command seeparator" between the generate.py and the simulate.py scripts. Either a newline or a semicolon would have worked; you didn't need the semicolon at the end of that line (though having it didn't hurt anything). –  John yesterday
    
or, as User112638726 suggested above use && instead of ; so that simulate.py only runs if generate.py finishes without error. e.g. for i in {1..100}; do python generate.py $i && python simulate.py $i ; done –  cas yesterday
    
you can also use set -e before the for loop and set +e after it to cause the entire loop to exit if any error occurs in any of the generate.py or simulate.py instances. this may or may not be what you want. –  cas yesterday
    
Thanks for the suggestion, @cas and @User112638726. If I wanted each command to only run if every command finished without error, would it be for i in {1..100}; do python generate.py $i && python simulate.py $i && done? –  Godwin Yung 11 hours ago
up vote 4 down vote

Yes, you are. A simple way to check would be to echo the commands instead of running them:

$ for i in {1..5}; do 
     echo python generate.py "$i"
     echo python simulate.py "$i" 
 done
python generate.py 1
python simulate.py 1
python generate.py 2
python simulate.py 2
python generate.py 3
python simulate.py 3
python generate.py 4
python simulate.py 4
python generate.py 5
python simulate.py 5

As you can see in the above example, the commands are launched as you want them.

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