Linux shell script to add leading zeros to file names

user_168646 0
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I have a folder with about 1,700 files. They are all named like 1.txt or 1497.txt, etc. I would like to rename all the files so that all the filenames are four digits long.

I.e., 23.txt becomes 0023.txt.

What is a shell script that will do this? Or a related question: How do I use grep to only match lines that contain \d.txt (i.e., one digit, then a period, then the letters txt)?

Here's what I have so far:

for a in [command i need help with]
do
  mv $a 000$a
done

Basically, run that three times, with commands there to find one digit, two digits, and three digit filenames (with the number of initial zeros changed).

grep shell linux bash
10 Answers

To provide a solution that's cautiously written to be correct even in the presence of filenames with spaces:

#!/usr/bin/env bash

pattern='%04d'  # pad with four digits: change this to taste

# enable extglob syntax: +([[:digit:]]) means "one or more digits"
# enable the nullglob flag: If no matches exist, a glob returns nothing (not itself).
shopt -s extglob nullglob

for f in [[:digit:]]*; do               # iterate over filenames that start with digits
  suffix=${f##+([[:digit:]])}           # find the suffix (everything after the last digit)
  number=${f%"$suffix"}                 # find the number (everything before the suffix)
  printf -v new "$pattern" "$number" "$suffix"  # pad the number, then append the suffix
  if [[ $f != "$new" ]]; then                   # if the result differs from the old name
    mv -- "$f" "$new"                           # ...then rename the file.
  fi
done
user_141220

There is a rename.ul command installed from util-linux package (at least in Ubuntu) by default installed.

It's use is (do a man rename.ul):

rename [options] expression replacement file...

The command will replace the first occurrence of expression with the given replacement for the provided files.

While forming the command you can use:

rename.ul -nv replace-me with-this in-all?-these-files*

for not doing any changes but reading what changes that command would make. When sure just reexecute the command without the -v (verbose) and -n (no-act) options

for your case the commands are:

rename.ul "" 000 ?.txt
rename.ul "" 00 ??.txt
rename.ul "" 0 ???.txt
user_19432090
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