mjhjmtu

I want to rename all the files in a folder with PREFIX+COUNTER+FILENAME

for ex.
input:

england.txt 
canada.txt 
france.txt

output:

CO_01_england.txt 
CO_02_canada.txt 
CO_03_france.txt

This does what you ask:

n=1; for f in *.txt; do mv "$f" "CO_$((n++))_$f"; done

How it works

• 
  

  n=1

  
  
  

  This initializes the variable n to 1.

  
  


• 
  

  for f in *.txt; do

  
  
  

  This starts a loop over all files in the current directory whose names end with .txt.

  
  


• 
  

  mv "$f" "CO_$((n++))_$f"

  
  
  

  This renames the files to have the CO_ prefix with n as the counter. The ++ symbol tells bash to increment the variable n.

  
  


• 
  

  done

  
  
  

  This signals the end of the loop.

  
  

Improvement

This version uses printf which allows greater control over how the number will be formatted:

n=1; for f in *.txt; do mv "$f" "$(printf "CO_%02i_%s" "$n" "$f")"; ((n++)); done

In particular, the %02i format will put a leading zero before the number when n is still in single digits.

With the prename utility found on Debian and derivatives or available on other systems by installing the Perl package Unicode::Tussle:

prename 's ([^/]*z) (sprintf("C0_%02d_%s", ++$n, $&))e' england.txt canada.txt france.txt

Explanation: for each argument, rename the base name (the longest suffix not containing a slash) to C0_ followed by the counter value $n (incremented before use, starting at 0 before the first incrementation and use) formatted to two decimal digits, followed by _, followed by the original name. To rename all files with the .txt extension, with the numbering in lexicographic order:

prename 's ([^/]*z) (sprintf("C0_%02d_%s", ++$n, $&))e' *.txt

With zsh, use the zmv function, and the parameter expansion flag l to pad the number:

autoload -U zmv
zmv '*.txt' '$f:h/C0_$(l:2::0:)$((++x))_$f:t'