Iterative file name in bash

Question

I want to iterate over different file names. The file names are XY1.txt, XY2.txt...XY500.txt. Each file that is taken as input generates 3 output files which I want to rename according to the current index. For XY1.txt, output1.txt becomes 1_1.txt, output2.txt becomes 1_2.txt and so on. But I do not know how to change the filename as per index. I looked it up but I was not finding what I needed on this website or elsewhere. I am new to bash. The below pseudo code is what I was able to write until now. Please help me out

    for i in {1..500} ; 
         filename = "XY"+str(i) + ".txt"  ;
         do ./CompiledCodeFile  -filename -use_option 4; 
         mv output1.txt str(i)+"_1.txt"   ;
         mv output2.txt str(i)+"_2.txt"   ;
         mv output3.txt str(i)+"_3.txt"   ;
    done

Wow, there's a lot of things that are wrong, let me correct it. — Fravadona
– Fravadona, Commented Nov 26, 2021 at 9:12

Fravadona · Accepted Answer · 2021-11-26 19:04:50Z

2

#!/bin/bash

for i in {1..500}
do
    filename="XY$i.txt"
    ./CompiledCodeFile  "$filename" -use_option 4
     mv output1.txt "${i}_1.txt"
     mv output2.txt "${i}_2.txt"
     mv output3.txt "${i}_3.txt"
done

notes:

$i and ${i}, what's the difference?

They're the same thing, but sometimes you need to use the ${} for differentiating the variable name from the following letters (here the _)

Why use double quotes for expanding variables, for example "$filename"?

Because that's almost mandatory. Not using double quotes is the cause of a lot of errors, while using double quotes can only be wrong for a very few cases (the only ones that I can think of is [[ xyz == $regexp ]] and the likes).
_{edited following @MikaelKjær comment.}

edited Nov 26, 2021 at 19:04

answered Nov 26, 2021 at 9:17

Fravadona

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6 Comments

Shaurya Goyal Over a year ago

I saw some Bash scripts for other uses where they use a semi colon. Why is that not necessary here ?

Fravadona Over a year ago

You can use a semi-colon OR a newline for separating commands

Fravadona Over a year ago

@MikaelKjær : ShauryaGoyal is a new bash user, so I can't possibly not use double quotes in my answer, even if it is not mandatory in his specific case...

Mikael Kjær Over a year ago

To be clear, I'm not criticizing you using quotes - I encourage it. It's the note I'm criticizing since it's just plain wrong. Your answer would be better without the second note.

Fravadona Over a year ago

@MikaelKjær : Well, my initial note was like a conclusion without prior explanations. Is it better after the edit?

|

Wen Wang · Accepted Answer · 2021-11-26 09:17:48Z

1

for i in `seq 500`; do
mv output${i}.txt ${i}_${i}.txt
done

use seq function to generate integer from 1 to 500
In bash, the type of variable is string in default.

answered Nov 26, 2021 at 9:17

Wen Wang

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2 Comments

M. Nejat Aydin Over a year ago

seq is not a function. It is an external application, though not specified by POSIX, a common utility. It is superfluous to spawn an external application to do some counting and then pass that application's output to bash for word splitting. In bash, C-style for loops are the best method for implementing a counter: for ((i=1; i<=500; i++))

M. Nejat Aydin Over a year ago

And the script doesn't do what the OP asked for.

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