Rerunning the same command with a different parameter

Question

I know that I can run the following command

ls Some{File,Folder} 

And it is equivalent to running this:

ls SomeFile SomeFolder 

(I also use it a lot for things like mv place_{a,b})

However, I was wondering if there was a different shortcut where I could do something like this:

run-command --a --whole --lot --of --flags parameter a; \ run-command --a --whole --lot --of --flags parameter b 

And I only had to type run-command --a --whole --lot --of --flags parameter {a,b} or something similar.

Answer 1

Assuming that you are using the GNU bash or something similar:

Perhaps a for loop?

for x in a b do run-command --a --whole --lot --of --flags parameter $x done 

which can also be written in one line as for x in a b; do run-command --a --whole --lot --of --flags parameter $x ; done

Answer 2

If you aren't scripting this and just want to run it easily on a command line, the xargs command is probably what you are looking for.

xargs will take a bunch of content from the standard input, and use it as arguments for a command, running that command multiple times if needed.

Try the following:

echo -n parameter a,parameter b | xargs -n 1 -d , run-command --a --whole --lot --of --flags 

Echo's -n flag avoids printing a trailing new line character (caused issues with some commands while passing parameters through).

In this example, you are simply giving xargs the permutations you want it to run.

The -n 1 flag to tell xargs to use just 1 of the arguments per run.

The -d , flag tells xargs to look for a "," on the input as the deliminator between arguments to run. (Note that if the argument has a "," in it you will need to change this to something else. If your arguments have no spaces in them you can omit this flag altogether.)

See man xargs for more info.

Answer 3

You can also use a function, which doesn't limit you to having your changing argument at the end:

runcom() { run-command --a --whole --lot --of --flags parameter "$1" ; } runcom a runcom b 

Answer 4

You can perform substitutions in the previous command. This won't work with your {a, b} example, because all instances of 'a' will be replaced with a 'b'. But imagine you want to execute the following commands:

run-command --a --whole --lot --of --parameter --format xml run-command --a --whole --lot --of --parameter --format son 

You can do it with

run-command --a --whole --lot --of --parameter --format xml !!:s/xml/json/ 

Bash will do the substitution and run

run-command --a --whole --lot --of --parameter --format json 

Use gs (global substitution) to perform several substitution, not only one.

Answer 5

There is alias command in bash:

$ alias shotcommand='run-command --a --whole --lot --of --flags parameter' 

The usage is: $ shotcommand a

Answer 6

xargs combined with your original suggestion of curly braces is handy here:

echo Ahoy{1,2,3}|xargs -n1 echo

Or with your example:

echo {a,b} | xargs -d' ' -I% echo run-command --a --whole --lot --of --flags parameter %

With the added %, you can place your parameter anywhere you want in the command.