For loops linux terminal

How to loop an executable command in the terminal in Linux?

Let me first describe my situation, I am working on a Linux platform and have a collection of .bmp files that add one to the picture number from filename0022.bmp up to filename0680.bmp . So a total of 658 pictures. I want to be able to run each of these pictures through a .exe file that operates on the picture then kicks out the file to a file specified by the user, it also has some threshold arguments: lower, upper. So the typical call for the executable is:

./filter inputfile outputfile lower upper 

Is there a way that I can loop this call over all the files just from the terminal or by creating some kind of bash script? My problem is similar to this: Execute a command over multiple files with a batch file but this time I am working in a Linux command line terminal.

6 Answers 6

You may be interested in looking into bash scripting.

You can execute commands in a for loop directly from the shell.

A simple loop to generate the numbers you specifically mentioned. For example, from the shell:

user@machine $ for i in ; do > echo "filename$.bmp" > done 

This will give you a list from filename22.bmp to filename680.bmp . That simply handles the iteration of the range you had mentioned. This doesn’t cover zero padding numbers. To do this you can use printf . The printf syntax is printf format argument . We can use the $i variable from our previous loop as the argument and apply the %Wd format where W is the width. Prefixing the W placeholder will specify the character to use. Example:

user@machine $ for i in ; do > echo "filename$(printf '%04d' $i).bmp" > done 

In the above $() acts as a variable, executing commands to obtain the value opposed to a predefined value.

This should now give you the filenames you had specified. We can take that and apply it to the actual application:

user@machine $ for i in ; do > ./filter "filename$(printf '%04d' $i).bmp" lower upper > done 

This can be rewritten to form one line:

user@machine $ for i in ; do ./filter "filename$(printf '%04d' $i).bmp" lower upper ; done 

One thing to note from the question, .exe files are generally compiled in COFF format where linux expects an ELF format executable.

Источник

Introduction to Linux Bash programming: 5 `for` loop tips

Every sysadmin probably has some skill they’ve learned over the years that they can point at and say, «That changed my world.» That skill, or that bit of information, or that technique just changed how I do things. For many of us, that thing is looping in Bash. There are other approaches to automation that are certainly more robust or scalable. Most of them do not compare to the simplicity and ready usability of the for loop, though.

If you want to automate the configuration of thousands of systems, you should probably use Ansible. However, if you’re trying to rename a thousand files, or execute the same command several times, then the for loop is definitely the right tool for the job.

If you already have a programming or scripting background, you’re probably familiar with what for loops do. If you’re not, I’ll try to break it down in plain English for you.

The basic concept is: FOR a given set of items, DO a thing.

Automation advice

The given set of items can be a literal set of objects or anything that Bash can extrapolate to a list. For example, text pulled from a file, the output of another Bash command, or parameters passed via the command line. Converting this loop structure into a Bash script is also trivial. In this article, we show you some examples of how a for loop can make you look like a command line hero, and then we take some of those examples and put them inside a more structured Bash script.

Basic structure of the for loop

First, let’s talk about the basic structure of a for loop, and then we’ll get into some examples.

The basic syntax of a for loop is:

The variable name will be the variable you specify in the do section and will contain the item in the loop that you’re on.

The list of items can be anything that returns a space or newline-separated list.

$ for name in joey suzy bobby;do echo $name;done

That’s about as simple as it gets and there isn’t a whole lot going on there, but it gets you started. The variable $name will contain the item in the list that the loop is currently operating on, and once the command (or commands) in the do section are carried out, the loop will move to the next item. You can also perform more than one action per loop. Anything between do and done will be executed. New commands just need a ; delimiting them.

$ for name in joey suzy bobby; do echo first $name;echo second $name;done; first joey second joey first suzy second suzy first bobby second bobby

Now for some real examples.

Renaming files

This loop takes the output of the Bash command ls *.pdf and performs an action on each returned file name. In this case, we’re adding today’s date to the end of the file name (but before the file extension).

for i in $(ls *.pdf); do mv $i $(basename $i .pdf)_$(date +%Y%m%d).pdf done

To illustrate, run this loop in a directory containing these files:

file1.pdf file2.pdf . fileN.pdf

The files will be renamed like this:

file1_20210210.pdf file2_20210210.pdf . fileN_20210210.pdf

In a directory with hundreds of files, this loop saves you a considerable amount of time in renaming all of them.

Extrapolating lists of items

Imagine that you have a file that you want to scp to several servers. Remember that you can combine the for loop with other Bash features, such as shell expansion, which allows Bash to expand a list of items that are in a series. This can work for letters and numbers. For example:

$ echo 0 1 2 3 4 5 6 7 8 9 10

Assuming your servers are named in some sort of pattern like, web0, web1, web2, web3, you can have Bash iterate the series of numbers like this:

$ for i in web;do scp somefile.txt $:;done;

This will iterate through web0, web1, web2, web3, and so forth, executing your command on each item.

You can also define a few iterations. For example:

$ for i in web db balance_;do echo $i;done web0 web1 web2 web3 web4 web5 web6 web7 web8 web9 web10 db0 db1 db2 balance_a balance_b balance_c

You can also combine iterations. Imagine that you have two data centers, one in the United States, another in Canada, and the server’s naming convention identifies which data center a server HA pair lived in. For example, web-us-0 would be the first web server in the US data center, while web-ca-0 would be web 0’s counterpart in the CA data center. To execute something on both systems, you can use a sequence like this:

$ for i in web--;do echo $i;done web-us-0 web-us-1 web-us-2 web-us-3 web-ca-0 web-ca-1 web-ca-2 web-ca-3

In case your server names are not easy to iterate through, you can provide a list of names to the for loop:

$ cat somelist first_item middle_things foo bar baz last_item $ for i in `cat somelist`;do echo "ITEM: $i";done ITEM: first_item ITEM: middle_things ITEM: foo ITEM: bar ITEM: baz ITEM: last_item

Nesting

You can also combine some of these ideas for more complex use cases. For example, imagine that you want to copy a list of files to your web servers that follow the numbered naming convention you used in the previous example.

You can accomplish that by iterating a second list based on your first list through nested loops. This gets a little hard to follow when you’re doing it as a one-liner, but it can definitely be done. Your nested for loop gets executed on every iteration of the parent for loop. Be sure to specify different variable names for each loop.

To copy the list of files file1.txt, file2.txt, and file3.txt to the web servers, use this nested loop:

$ for i in file;do for x in web;do echo "Copying $i to server $x"; scp $i $x; done; done Copying file1 to server web0 Copying file1 to server web1 Copying file1 to server web2 Copying file1 to server web3 Copying file2 to server web0 Copying file2 to server web1 Copying file2 to server web2 Copying file2 to server web3 Copying file3 to server web0 Copying file3 to server web1 Copying file3 to server web2 Copying file3 to server web3

More creative renaming

There might be other ways to get this done, but remember, this is just an example of things you can do with a for loop. What if you have a mountain of files named something like FILE002.txt, and you want to replace FILE with something like TEXT. Remember that in addition to Bash itself, you also have other open source tools at your disposal, like sed , grep , and more. You can combine those tools with the for loop, like this:

$ ls FILE*.txt FILE0.txt FILE10.txt FILE1.txt FILE2.txt FILE3.txt FILE4.txt FILE5.txt FILE6.txt FILE7.txt FILE8.txt FILE9.txt $ for i in $(ls FILE*.txt);do mv $i `echo $i | sed s/FILE/TEXT/`;done $ ls FILE*.txt ls: cannot access 'FILE*.txt': No such file or directory $ ls TEXT*.txt TEXT0.txt TEXT10.txt TEXT1.txt TEXT2.txt TEXT3.txt TEXT4.txt TEXT5.txt TEXT6.txt TEXT7.txt TEXT8.txt TEXT9.txt

Adding a for loop to a Bash script

Running for loops directly on the command line is great and saves you a considerable amount of time for some tasks. In addition, you can include for loops as part of your Bash scripts for increased power, readability, and flexibility.

For example, you can add the nested loop example to a Bash script to improve its readability, like this:

$ vim copy_web_files.sh # !/bin/bash for i in file;do for x in web;do echo "Copying $i to server $x" scp $i $x done done

Great DevOps downloads

When you save and execute this script, the result is the same as running the nested loop example above, but it’s more readable, plus it’s easier to change and maintain.

$ bash copy_web_files.sh Copying file1 to server web0 Copying file1 to server web1 . TRUNCATED . Copying file3 to server web3

You can also increase the flexibility and reusability of your for loops by including them in Bash scripts that allow parameter input. For example, to rename files like the example More creative renaming above allowing the user to specify the name suffix, use this script:

$ vim rename_files.sh # !/bin/bash source_prefix=$1 suffix=$2 destination_prefix=$3 for i in $(ls $*.$);do mv $i $(echo $i | sed s/$/$/) done

In this script, the user provides the source file’s prefix as the first parameter, the file suffix as the second, and the new prefix as the third parameter. For example, to rename all files starting with FILE, of type .txt to TEXT, execute the script like this :

$ ls FILE*.txt FILE0.txt FILE10.txt FILE1.txt FILE2.txt FILE3.txt FILE4.txt FILE5.txt FILE6.txt FILE7.txt FILE8.txt FILE9.txt $ bash rename_files.sh FILE txt TEXT $ ls TEXT*.txt TEXT0.txt TEXT10.txt TEXT1.txt TEXT2.txt TEXT3.txt TEXT4.txt TEXT5.txt TEXT6.txt TEXT7.txt TEXT8.txt TEXT9.txt

This is similar to the original example, but now your users can specify other parameters to change the script behavior. For example, to rename all files now starting with TEXT to NEW, use the following:

$ bash rename_files.sh TEXT txt NEW $ ls NEW*.txt NEW0.txt NEW10.txt NEW1.txt NEW2.txt NEW3.txt NEW4.txt NEW5.txt NEW6.txt NEW7.txt NEW8.txt NEW9.txt

Conclusion

Hopefully, these examples have demonstrated the power of a for loop at the Bash command line. You really can save a lot of time and perform tasks in a less error-prone way with loops. Just be careful. Your loops will do what you ask them to, even if you ask them to do something destructive by accident, like creating (or deleting) logical volumes or virtual disks.

We hope that Bash for loops change your world the same way they changed ours.

Источник